Notes: The Art of Stargazing Month 1: February - March 2013

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1 Notes: The Art of Stargazing Month 1: February - March 2013 Copyright 2013 Mintaka Publishing Inc.

2 -2- Contents The Art of Stargazing (Month 1) What You Will Learn This Month... 3 Tour of the Night Sky Orion, Taurus, Auriga, Canis Major... 3 The Constellation Orion... 3 The Constellation Taurus... 6 The Constellation Auriga... 9 The Constellation Canis Major The Constellations Monoceros and Lepus The Constellation Eridanus Constellations vs. Asterisms Observing Techniques Visual Observing Science of Astronomy - Layout of the Night Sky The Layout of the Night Sky The Celestial Poles and the Celestial Equator The Ecliptic Measuring Angles in the Night Sky The Deep Sky This Month Winter Clusters The Hyades The Pleiades The Great Orion Nebula The Orion OB1 Association The Crab Nebula M41 in Canis Major M36, M37, and M38 in Auriga Solar System Observing A Brief Tour; Jupiter What You Have Learned This Month... 42

3 -3- What You Will Learn This Month In this first month of the Art of Stargazing, you jump right in with a tour the prominent constellations of the northern winter sky as seen in late February and March. Once you learn to find your way around a little, you also learn how to find a handful of the brightest and easiest-tosee star clusters and nebulae visible this time of year. And you will meet Jupiter, the largest planet in our solar system. You also find out how your eyes see in the dark, as well as how to best condition your eyes for viewing astronomical objects. This is an essential skill for every stargazer, and you will use this knowledge when observing with binoculars and telescopes too. Let s get started... Tour of the Night Sky Orion, Taurus, Auriga, Canis Major Let s begin the sky tours with the most famous and unmistakable constellation in the heavens, Orion, which will serve as a guide for other bright constellations in the late winter sky. Note: This tour is for the sky as it appears in late February and March It will appear the same in subsequent years except for the location of solar system objects like Jupiter and the Moon. The Constellation Orion Head outdoors around 7 p.m. or 8 p.m. on an evening in late February or early March, and turn towards the south. If you can t find south, you can ask someone else, or get a small inexpensive compass, or use the GPS in your smartphone or tablet. But you need to face at least generally southward before you can proceed. You will also need a good view of the sky in the south, so you may need to get away from structures and trees and so on. And bring a pair of binoculars if you have them, though they are not necessary for this tour. Now that you re facing south with a good view of a clear sky, look for bright stars. There are quite a few in this part of the sky. You are looking, in particular, for the tell-tale shape of the constellation Orion, which you can see in the map below. Orion depicts a hunter standing upright, as seen from the northern hemisphere, adorned with a belt and sword, and holding a westward facing shield in his left hand and an upraised club in his right. Note: The maps in this tour are accurate for 45 degrees north latitude. If you live north of this latitude, Orion will appear slightly closer to the horizon. If you live south of this latitude, the stars appear further above the horizon.

4 -4- The bright stars of the constellation Orion Most observers recognize Orion by the three bright stars of his belt. These stars line up on a slight diagonal as seen from most parts of the northern hemisphere, and span about the same width as your three largest fingers held together at arm s length. Well above the belt lies two brighter stars. The brighter left star is clearly orange-red. This is the star Betelgeuse ( BAYtell-jewz ). It marks one of the shoulders of Orion. The right star is whitish-blue and goes by the name of Bellatrix. Below the belt lies two more bright stars marking Orion s feet. The brilliant blue left (or westward) star is Rigel ( RYE-jel ). The eastern star is called Saiph ( safe ).

5 -5- Take a moment to marvel at this splendid constellation. Glittering like a gigantic tapestry of celestial jewels, the constellation holds a number of the brightest stars in the sky in close proximity to each other. Many of these stars formed at the same time from the vast and invisible mass of gas and dust in this part of the sky. As you will see shortly, new stars are being formed here even now. The bright red-orange star marking Orion s shoulder, called Betelgeuse, is a massive red supergiant star that s burned through most of its fuel and is nearing the end of its life. It will explode, some time in the next million years or so, as a supernova that shines so bright it will cast shadows by night and be visible in our daytime for several weeks. At present, the core of the star has shrunk and grown hotter, which in turn has caused the outer layers of the star to expand. So Betelgeuse is immense: if it were to replace our Sun at the center of our solar system, the visible surface of the star would extend to the orbit of Jupiter! You will learn more about how stars evolve through their lifetimes later in this program. Image of the star Betelgeuse (credit: NASA) Betelgeuse lies about 650 light years from Earth, which means the light you see now has been travelling towards Earth for 650 years. Rigel ( RYE-jel ), which marks one of Orion s feet, is on the other side of the evolutionary scale. This star is massive, like Betelgeuse, but it s much younger and still burns hydrogen in its core. So its core is cooler, its outer layers more compact, and its surface is hotter (12,000 K) than Betelgeuse (3,500 K). Rigel is also slightly brighter than Betelgeuse. Indeed, only five stars in the entire sky outshine Rigel. Three stars lined up in a tidy row mark Orion s Belt. These stars are, from east to west (or left to right) Alnitak, Alnilam, and Mintaka. Like Rigel, these stars are also young, massive, blue-white stars. They will also end their lives, like most of the bright stars of Orion, in brilliant supernovae explosions in the distant future. These stars are a chance alignment: each lies at a different distance. Alnitak, Alnilam, and Mintaka are 800, 1340, and 915 light years from Earth, respectively. If you have binoculars handy, turn them to Orion s Belt to see many fine arrangements of bright blue-white stars, including a winding S-shaped group between Mintaka and Alnilam. Arab

6 -6- astronomers once called Orion s Belt the String of Pearls, but in binoculars it looks more like a web of diamonds. Halfway between and a little north (or above) the shoulders of Orion, look for the small patch of fainter stars that mark the hunter s relatively faint head. To your unaided eye, the patch may appear cloud-like and unresolved. If your eyes are keen, you may detect three stars here. These stars are called phi-1 Orionis, phi-2 Orionis, and lambda Orionis (also known as Meissa). If you have your binoculars handy, look at these three stars. Your optics will reveal a pleasant surprise: some faint stars spread among the three brighter stars. Many are part of the same cluster of newborn stars. Finally, look closely at the group of three dim stars that appear to hang off the belt. In binoculars or a small telescope, the middle star appears fuzzy and indistinct, because it s entangled in a mass of glowing gas and dust called the Orion Nebula where a cluster of brand-new stars are in the process of formation. You will learn more about this nebula and other objects in Orion s sword later in this month s program. As a constellation, Orion has been known since antiquity. The Sumerians depicted these stars as their legendary hero Gilgamesh. The starry hero was seen as fighting a celestial bull, the V- shaped congregation of stars now known as Taurus, which we will visit next. Despite the prominence of these stars, the Greeks assigned them a less noble namesake. Orion was a mighty hunter, to be sure, but he was a bit of a dim-witted brute. One legend tells of the hunter madly killing the Earth s animals until too few remained. The goddess Artemis put an end to Orion s greed by sending the fearsome scorpion Scorpius to sting the hunter, killing him instantly. Another version of the legend has Orion pursuing Artemis with romantic inclinations before the virginal goddess unleashed the Scorpion. In both cases, Artemis regretted the death of the hunter and asked Zeus to place Orion and Scorpius in the heavens at opposite ends of the sky. The Constellation Taurus Using Orion as a base of operations, you can now navigate to other prominent constellations. Extend a line from Orion s Belt toward the northwest (the upper right as seen from the northern hemisphere in the early evening hours in late winter). You will arrive at a bright orange star. This is Aldebaran, the brightest star in the constellation Taurus, the Bull. Like Orion, Taurus was one of the 48 original constellations included in the maps of the ancient astronomer Ptolemy in the 1st century A.D. Note: In 2013, you will also see an even brighter object shining with pale yellow color near Aldebaran. This is the planet Jupiter.

7 -7- Orion s Belt points the way to the constellation Taurus, with Jupiter visible in early 2013 The bright star Aldebaran ( all-deb-a-run ) is a swollen giant star some 45x the diameter of our own sun. It s far smaller and intrinsically fainter than Betelgeuse in Orion, but still appears bright because it lies just 65 light years away, about ten times closer than Betelgeuse. A much smaller group than Orion, Taurus is still one of the loveliest constellations of the northern winter sky. This ancient constellation holds two open star clusters, the Hyades and the Pleiades, both of which are a magnificent sight with the unaided eye or with binoculars. The Hyades cluster is the little V-shaped group of stars to one side of Aldebaran. It is a large and nearby cluster and one of the prettiest and easiest to observe with binoculars. This star cluster lies about 135 light years away, which means Aldebaran is not a member, but merely a foreground object. The V-shape of Taurus resulted in the mythical association of these stars with the head of a bull since at least 4000 B.C., and ancient Babylon, Egypt, and Greece noted these stars as a major

8 -8- constellation. The name Taurus means bull in Latin. The small patch of V-shaped stars marks the head of the bull. The star at the nose of the bull is gamma Tauri. Aldebaran marks the eye. Extend each arm of the V of Taurus to find the tips of the horns marked by the stars zeta Tauri and beta Tauri, sometimes called Elnath or Alnath. The Pleiades cluster lies a little further on the same line from Orion s Belt through the V of Taurus. The cluster is a tiny dipper-shaped patch of stars smaller than your little fingernail held at arm s length. You can see perhaps six stars in the cluster without optical aid. Alcyone is the brightest. You will examine the Hyades and Pleiades star clusters in more detail shortly. But first, let s follow the horns of the celestial bull to Auriga, another prominent constellation. The constellation Taurus and the Pleiades

9 -9- The Constellation Auriga Now to the constellation Auriga ( or-eye-gah ). This large hexagonal constellation lies directly north of Orion and is marked by its brightest star, the yellow-white Capella which lies high overhead on an early evening in February and March about two full hand lengths above Rigel. The Greeks had a number of legends associated with this ancient constellation, but they all involve some form of charioteer, likely because the peaked shape of the constellation resembles the rider s helmet. The conventional legend has Auriga representing Erichthonius, a king of Athens who was raised by Athena and invented the quadriga, a four-horse chariot. The Babylonians also related this star group to a chariot. So did the Chinese, who saw the stars Capella (alpha), beta, theta, and iota Aurigae along with Alnath (β Tauri) representing the chariots of five celestial emperors. The stars epsilon (ε), zeta (ζ), and eta (η) Aurigae are tethering poles for the horses. Auriga looks like a large hexagon spread over some 15º of sky. The brightest star, Capella, is a dazzling yellow-white giant star and one of the three brightest in the northern hemisphere. Capella contrasts nicely with the blue-white Menkalinan ( men-kah-li-nan ). The stars theta, iota, and zeta round out the hexagon, along with Alnath, which actually belongs to the constellation Taurus. Alnath (blue) and ι Aur (orange) also contrast nicely. Capella, which is an intriguing quadruple star system, takes its name from the Latin for little she-goat carried by the charioteer on his shoulder, presumably. The triangular grouping of stars epsilon (ε), zeta (ζ), and eta (η) Aurigae are often called The Kids. The Kids and Capella fit into the same field of view in most binoculars, and they are a lovely sight. Though you can t tell simply by looking, you are seeing stars here of very different distances. Capella is just 40 light years away, eta is 220 light years, zeta is 850 light years, and epsilon is some 2,000 light years away. Epsilon is an extremely bright star (intrinsically), and it has a strange companion star shrouded in dark dust that eclipses the main star every 27 years. The last eclipse occurred in If you have binoculars, look at the region between iota Aurigae and Alnath. It is particularly fine, with a spray of hundreds of faint stars visible in dark sky.

10 -10- The constellation Auriga The Constellation Canis Major Orion s Belt guided us north and west to the constellation Taurus, and it also points the way, in the other direction, to the constellation Canis Major, the Big Dog. As you turn your gaze towards Canis Major, you will be immediately struck by a blazing bluewhite star. This is Sirius, the brightest star in the heavens, and it marks the neck of Canis Major. The star s name comes from the ancient Greek seirios, meaning scorcher. Twice the mass and 25 times more luminous than the Sun, Sirius is a modest star as stars go. It s not as intrinsically bright as monster stars like Rigel and Betelgeuse. It simply appears bright because it s the 5th closest star to Earth, only 8.6 light-years away, some 80x closer than Betelgeuse.

11 -11- Orion s Belt points the way to Canis Major and the bright star Sirius Because it lies low in the sky as seen from the northern hemisphere, Sirius often twinkles aggressively. This is an effect caused by the thick atmosphere near the horizon, which momentarily bends the star s light causing an apparent movement and color change. As you look at Sirius over a number of evenings, watch this normally blue star appear to flash white, yellow, green, and even red. Although many think of Sirius as a winter star, the ancient Romans and Greeks associated Sirius with the heat of summer because it rises just before dawn near the summer solstice. According to Virgil, its influence was considered unfortunate, bringing drought and diseases on sickly mortals. And it s the same with the host constellation. In ancient times, the Greeks noted the Canis Major rose before sunrise during the hot, late days of northern summer, during which they noted only a dog would venture into the heat. These dog days lent their name first to Sirius, which is sometimes called the Dog Star, and eventually to the entire constellation. The celestial Big Dog, along with the much smaller constellation Canis Minor, the Little Dog, are often depicted accompanying the great hunter Orion. Canis Minor is marked by the bright star Procyon ( PRO-see-on ) just to the east of Betelgeuse. Ancient Greek poet Aratus, the forgotten poet of stargazers, wrote of Canis Major as Orion s guard dog. Canis Major was also

12 -12- one of Ptolemy s original 48 constellations from the 1st-century A.D., though it was named much earlier. Canis Major is populated with mostly young blue stars and star clusters of the Orion Arm of our galaxy. The constellation contains several first and second-magnitude stars which stand out well in this rich section of the Milky Way. As you inspect the constellation, look also for the star Mirzam. Its name means The Herald, presumably because it precedes brilliant Sirius as it rises. Although it s cataloged as beta Canis Majoris, which suggests it should be the 2nd brightest star in the constellation, it is actually the 4th brightest. The star Adhara, the second-brightest star of Canis Major is also worthy of note. Five million years ago, this star was much closer to the Sun and was, for a time, the brightest star in the sky. The brightest stars of the constellation Canis Major; the constellation Monoceros The Constellations Monoceros and Lepus Directly east (or left) of Orion lies the dim constellation Monoceros, which represents a celestial unicorn. It holds no bright stars and is often overlooked for brighter Orion and Taurus and Canis Major. Seeing the outline of a unicorn in this dim patch of stars is nearly as challenging as seeing a real unicorn. If you re in the city, you ll find it hard to spot any stars at all.

13 -13- You might think a constellation that sits near to Orion and takes its name from a unicorn has a long and rich history dating to classical times. But this is not so. Monoceros is a fairly new constellation, and the Greeks had no legends of unicorns. The constellation was first included on a star chart by Petrus Plancius in the early 1600 s, and formalized by Jakob Bartsch in his star charts later in the 17th century. Look also for the tiny constellation Lepus ( LEE-puss ) just south of the great hunter Orion. There are many legends of how Lepus came to be among the stars. The Roman writer Hyginus wrote of a man who brought hares to the island of Leros to raise them for food. A few escaped, and before long the island was overrun with voracious rabbits who consumed crops and caused a famine among the human population. The hares were eventually driven out, but the inhabitants placed Lepus among the stars as a reminder of their experience. The poor celestial hare forever runs from the Big Dog, Canis Major. Perhaps that s why he s cowering in the hopes of a little protection at the feet of the great hunter. The Constellation Eridanus Near Rigel at Orion s left foot begins the long constellation Eridanus ( air-rid-in-us ), the River, which winds from the foot of Orion into the deep southern sky below the horizon. The constellation has a rich history, and takes its name from the ancient Greek name for the Po River in northern Italy. Eridanus dates back to the 1 st and 2 nd century A.D., when the astronomer Ptolemy included it in his original list of 48 constellations. Eridanus begins near the star Cursa, just west of Rigel, in Orion, and moves straight west, cuts back east, then drops directly south. Only stargazers in the southern hemisphere can see all of it, including the bright star Achernar at the end of this celestial river. The constellation lies nearly overhead for observers in the southern hemisphere. Have a look at the close pairing of stars just south and west of Rigel. Astronomers cataloged these two stars as omicron 1 and omicron 2. Omicron-1 is called Beid ( BYED ). Omicron 2, which is the fainter of the two, is also called 40 Eridani or Keid ( KYED ) It s a binary star, a two-star system, just 16 light years away from Earth. The main component, called 40 Eridani A, is a red dwarf star, just slightly smaller than our Sun. If you re a big Star Trek fan you may know that 40 Eridani A is the fictional home star of the planet Vulcan and Mr. Spock. There is not yet any sign of any life in this star system, however!

14 -14- The constellations Lepus, the Hare, and Eridanus, the River to the south and west of Orion Constellations vs. Asterisms Constellations, of course, are groups of stars organized into patterns that are meant to resemble mythological figures or other types of objects. The stars within each constellation are usually not physically related, and they don t even lie at the same distance. But they are helpful constructions to help astronomers organize the sky. Many constellations were invented in ancient times, especially by the ancient Greeks. An early list of 48 constellations was developed by the astronomer Ptolemy in the 1 st and 2 nd -centuries A.D. As we ve seen, his list included the brightest and most prominent constellations like Orion, Taurus, and Auriga. Other constellations were added much later, in the 16th-18th centuries A.D., to fill patches of sky left blank by Ptolemy. In 1930, the International Astronomical Union (IAU) formalized a list of 88 constellations that cover the entire sky, including the sky seen from the southern hemisphere. No changes have been made to this list since it was first developed. All objects on the celestial sphere lie within one of these 88 constellations.

15 -15- Few amateur astronomers (or even professionals, for that matter) can name all 88 constellations. As a newcomer, you will do well to learn of the largest and brightest constellations. In time, you will acquaint yourself with the tiny, dim, and barren constellations that essentially just fill in the gaps of the sky. Some groups of stars form easily identifiable shapes but are not constellations. The Big Dipper is an example. So is the Little Dipper, and the Summer Triangle, and Orion s Belt. These groups, which are formed from stars within a single constellation or from several constellations, are called asterisms. You will meet many asterisms as you tour the sky throughout this program... Observing Techniques Visual Observing Whether you look through $50 binoculars or an a $10 million telescope, whether you observe a single star or a galaxy of 500 billion suns, all the ancient starlight you hope to see passes through the tiny 7 mm-wide-lens of your eye and falls on a delicate retina just 1.5 mm across. Your eyes are a work of art in themselves, the culmination of 100 million years of evolution, exquisite tools to help you see the the beauty and danger and opportunity of our own world. But they are not optimized for stargazing. With their larger and more sensitive eyes, cats and hawks and eagles, among others, would have a far better view of the night sky than us. But we have the brains to understand what we see, so we need to understand how to extract as much detail and sensitivity from our eyes as nature will allow. The retina of your eye has two types of light-detecting cells: rods and cones (see image below). Cone cells detect color under well-lit conditions and are densely packed in the fovea, the area on the back of your eye near the center of your retina. Cones let you see color and fine detail when you look at, for example, books, movies, and faces. To get the most detailed view of bright objects, you must look directly at objects to expose the part of your retina where the cones are most densely concentrated. That s why you can only read the words on this page when you look at it directly. Look slightly off to one side, and you can t see enough detail to read.

16 -16- Cross-section of the retina Rod cells also lie on your retina, but away from the fovea. As it turns out, because of the distribution of the rods on your retina, you can see the faintest objects if you look 8 to 16 degrees off center. The exact angle is a little different for each person. This only works if the object you re looking at is on the nose-ward side of your eye. So look slightly rightward with your right eye and leftward with your left eye. Do the reverse and you ll expose the blind spot of your eye and you won t see a thing. This technique of looking off to one side to see faint objects is called averted vision. With this technique, you can objects 20-40x fainter than if you look straight on. That's a huge increase. When you first try averted vision, you will be shocked at the subtle detail that suddenly appears. If you re using both eyes, as with binoculars, you can still use averted vision. Of course, looking only sideways makes one eye more sensitive at the expense of the other. The solution? Look up. That uses another rod-rich part of your retina above the fovea. Rods are most sensitive to bluegreen light, but your optic nerve and brain are not wired to detect color when only your rod cells are exposed to light. That s why faint objects appear grayish-white through all but the largest telescopes. Before you can use averted vision, however, you must ensure your eyes are prepared to see faint objects. Your eye actually operates in two modes, scotopic and photopic. In photopic mode, the cones are optimized to detect bright light and colors. But in scotopic mode, the rods are set to detect faint light in dark conditions. For astronomy, you need to get your eye in scotopic mode, a state also known as dark adaptation. Both types of cells in your retina, rods for bright light and cones for faint light, contain dyes that undergo a chemical change called bleaching when hit by light. In light-adapted or photopic mode, the dyes in your rods are fully bleached, so they re out of action. Turn the lights off and the rods to return to scotopic mode, but it takes a long time, about minutes. That means you can't just walk out of a bright room and expect to see much through a telescope, whether you

17 -17- use averted vision or not. You must wait at least 10 minutes (preferably more) for your eyes to begin to enter scotopic, or dark-adapted mode. Going from a scotopic to photopic state happens much faster, in only a few seconds. That's why astronomers get quite angry when someone carelessly shines a bright white light in their eyes they lose their dark adaptation almost immediately, and they have to wait a long time to recover it. Each eye reacts separately to light, so you can keep one eye dark adapted while using your other eye to read star charts and move your telescope. An eye patch is ideal to keep one eye completely dark adapted. You can also keep unwanted streetlights out of your eyes by throwing a towel over your head when looking through the eyepiece of your scope with your dark adapted eye. Spectral sensitivity of rods and cones. Notice cone cells are not sensitive to light with wavelengths longer than 650 nm You often see astronomers using bright red LED flashlights when looking at star maps and gear around the telescope. Doesn't the bright red light ruin their dark adaptation? No... because red light cannot bleach the dye in the rods if the wavelength is > 650 nanometers (see above). So the chemical structure of the dye in the rod cells is completely unaffected by red light, while the dye in the cones still enables scotopic vision. Your body cannot by itself make the dyes for the rods and cones in your retina. It needs an external chemical-- beta carotene-- to synthesize the dyes. A good source of beta cartone? Carrots. So carrots really can be good for your eyesight. Grape-seed extract is also supposed to help night vision.

18 -18- Dark adaptation is not critical for casually observing bright stars and constellations. But you will always see more if you give your eyes time to adjust to the dark, and keep even brief flashes of bright light out of your eyes. A red flashlight for astronomy, a critical tool for seeing in the dark without ruining your sensitive night vision. Science of Astronomy - Layout of the Night Sky You ve started this first month of The Art of Stargazing with a tour of Orion, Taurus, Canis Major and many other prominent constellations. These bright constellations are fairly easy to find compare do most. To find fainter constellations in the later tours, and to understand the motion of the sky through the year, it helps to understand the layout of the sky. Here are the basics... The Layout of the Night Sky Look up on a clear night and you ll notice the sky looks like a vast hemispherical dome with stars fixed to its inner surface. If the Earth were transparent, you would see the stars on the other half of this starry dome, below your feet, and you d get the impression you were standing at the center of a velvety-black sphere speckled with stars. Astronomers call this the celestial sphere. While it appears that all stars are fixed to the celestial sphere, they are in fact at very different distances, but you cannot directly perceive this simply by looking into the sky. Ancient stargazers mused the stars may be tens or hundreds of miles away, and thought the stars were holes in the sky to let through the light of heaven. The stars are in fact tens of trillions of miles

19 -19- away, and are balls of burning gas sustaining themselves through gravitational forces and the energy from nuclear reactions in the cores. But back to the layout of the sky. The line at which the earth's surface and the sky appear to meet is called the horizon. If you re surrounded by structures, trees, and hills, It may be hard to see the horizon. But if you re on a prairie or desert or the ocean, you should have little trouble seeing the sky down to the horizon. The horizon, where the sky appears to meet the Earth The imaginary point on the celestial sphere that is directly overhead, and therefore 90 degrees above the horizon, is called the zenith. The point that is 90 degrees below the horizon, which of course you cannot see, is called the nadir. The imaginary points on the horizon which indicate the main directions, north, south, east, and west are known as cardinal points (see below). If you ve see Orion in this month s sky tours, for example, you were facing south, more or less. To find north-- true north-- you need to find the North Star, also known as Polaris. To find Polaris, look first for the Big Dipper, which is a large dipper-shaped group of stars in the northeastern sky. At this time of year (mid-winter in the northern hemisphere), the Dipper is standing on its handle in the mid-evening hours. Here s what you re looking for... Look for the front stars of the bowl of the Dipper. They are called The Pointers because they point the way to the North Star. Follow the pointers, as in the diagram above, for a distance of about five times the distance between these two stars. You will arrive at a moderately bright star. This is Polaris, the North Star. When you are facing Polaris, you are facing north.

20 -20- Polaris, by the way, marks is the brightest star in the asterism called the Little Dipper, which is smaller and fainter than the Big Dipper. If you are inclined, see if you can trace out the other stars of the Little Dipper. The Pointers of the Big Dipper show the way to Polaris, as seen in the evening hours of February and March Now that you ve found north, it s time to trace another key feature of the celestial sphere. Guide your imagination to the imaginary great circle that runs from the northern horizon, up through Polaris, through the zenith, then down to the southern horizon. This circle called the meridian. The meridian is important to stargazers for a number of reasons. For now, simply note that when a star is near the meridian, it s at its highest point in the sky during the night, and therefore it s at its optimum position for observation. When an object appears to move east to west through the meridian during the evening, a movement caused by the Earth s rotation, the object is said to culminate.

21 -21- The horizon, meridian, and cardinal points The Celestial Poles and the Celestial Equator There are a few more important features of the celestial sphere... First, Polaris also marks-- almost-- the position of the North Celestial Pole (NCP). It lies directly above the Earth s north pole. Which means if you were standing at the Earth s north pole, the North Celestial Pole is the imaginary point directly over your head. Polaris is not exactly at the NCP, though it is, by chance, very close... less than one degree. The celestial poles and equator lie above their terrestrial counterparts

22 -22- Same story for the south... the South Celestial Pole (SCP) is directly above the Earth s south pole. There is no bright star near the SCP, that is, there is no southern counterpart to Polaris. And as it is with the poles, so it is with the equator. Directly above the Earth s equator lies the Celestial Equator, which divides the northern half of the celestial sphere from the southern half. As you can see from the image above, if you were standing at the north pole, the celestial equator would coincide with the horizon. And if you were standing on the Earth s equator, the celestial equator would stretch from the south to the north directly overhead (so it would follow, exactly, the meridian). And as seen from the equator, the north and south celestial poles would lie on the northern and southern horizon, respectively. But how about if you re standing at some intermediate latitude, between the north pole and the equator? In that case, the north celestial pole (NCP) would lie at some angle above the northern horizon. That angle is equal to your latitude. If you are at the equator, which is 0 degrees latitude, then the NCP (and Polaris) would lie zero degrees about the horizon, that is, on the horizon. At 10 degrees latitude, Polaris will lie 10 degrees above the horizon. And in London, England, which has latitude 51 degrees, Polaris will lie 51 degrees above the horizon. This is how navigators have determined their latitude for thousands of years... by measuring the angle of Polaris above the horizon. The Ecliptic Now to one last key circle on the sky: the ecliptic. The ecliptic is another great circle around the celestial sphere, just like the celestial equator. But the ecliptic is tilted with respect to the equator by 23.5 degrees (see below). The ecliptic is the imaginary circle on the sky that marks the annual path of the Sun. It s tilted because the Earth itself is tilted relative to its orbit around the Sun by 23.5 degrees (see below).

23 -23- The tilt of the Earth s axis, showing the plane of the ecliptic inclined to the celestial equator and the position of the equinoxes and solstices. Because of this tilt, the Sun appears highest in the sky relative to the celestial equator when the Earth is at one position in its orbit. This happens on or about June 21, and we call this the summer solstice (in the northern hemisphere). When the Earth is at the opposition side of its orbit in December the Sun is at its lowest point in the sky relative to the celestial equator. This is the winter solstice. Between the two, the Sun is right on the celestial equator. These are spring and autumnal equinoxes when spring and autumn begin. The equinoxes and solstices are four points on the ecliptic. What s more, since all the planets lie near the same flat plane around the Sun, the ecliptic also marks the path of the planets around the sky as they revolve around the Sun. So every planet, the Sun, and even the Moon, are always found on or very close to the ecliptic during the year. As it turns out, the great circle of the ecliptic passes through 12 of the 88 constellations. This group of constellations is called the zodiac, which includes Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces. (The ecliptic actually passes through a 13th constellation, Ophiuchus, but it is not included in the zodiac because ancient astrologers regarded the number 13 as unlucky). Example: The image below helps bring the above ideas together for you. It shows a wide-angle simulation of the night sky in mid-february about 8 p.m. from a latitude of 45 degrees north. You see three

24 -24- of the four cardinal points around the horizon (north is not shown). You see the green line representing the meridian stretching from the south, overhead, off through to the north; Polaris is the brighter star at the top of the image near the M in Meridian, and nearly on the meridian. You see the ecliptic in red and the celestial equator in blue. Notice how Orion s Belt nearly lies on the equator, and the planet Jupiter lies along the ecliptic. You also see the star Betelgeuse is culminating, that is, crossing the meridian at its highest point in the sky for the evening as it moves from east to west. A wide-angle view of the sky looking south in the evening in February/March showing the meridian (green), the celestial equator (blue), and the ecliptic (red) You ve covered a lot here. Who would have thought the sky has some many points and great circles? It may all seem a little confusing at first. But don t worry. You just need to review this material, think about it on your own, and trace out these points and circles in the heavens. In time, it will all become second nature as you work through The Art of Stargazing.

25 -25- Measuring Angles in the Night Sky As you learn to find your way around the night sky, it is immensely helpful to know how to estimate angles. For example, if you read the star cluster M41 is 4 degrees south-southeast of the star Sirius, you want to have some idea of what that means. There are, as you may recall, 360 degrees in a circle. The north and south cardinal points on the horizon, for example, at 180 degrees apart. And the angular separation of any point on the horizon and the point directly overhead (the zenith) is 90 degrees. Halfway from the zenith to the horizon is 45 degrees. So far, so good. Smaller angles are a little trickier. But your hands and fingers are a remarkably accurate (and convenient) measuring tool. When you hold your hand at arm s length, you can estimate angles like this: Stretch your thumb and little finger as far from each other as you can. The span from tip to tip is about 25 degrees Do the same with your index finger and little finger. The span is 15 degrees. Clench your fist at arm s length, and hold it with the back of your hand facing you. The width is 10 degrees Hold your three middle fingers together; they span about 5 degrees The width of your little finger at arm s length is 1 degree. These measures work even for kids because while their arms are shorter, their hands are smaller.

26 -26- Using your fingers to measure angles in the sky The Deep Sky This Month Winter Clusters As you get a feel for the bright star and constellations and the layout of the night sky, you will want to see more. Much more. The Moon and planets are excellent targets, and you will meet them soon. But beyond our solar system lies what stargazers call the deep sky, the limitless expanse of space that holds untold numbers of nebulae, star clusters, and strange stars within our own galaxy, as well as millions of galaxies far beyond our own. You will learn the nature of these objects of the deep sky as you move through the course. But let s look at a few right now as you continue your tour of the northern winter sky. Indeed, you have already seen two deep-sky objects during the constellation tours: the Hyades and the Pleiades. Let s start the tour there... Note: A pair of binoculars is useful to see these deep-sky objects, and in some cases, a telescope is helpful too. If you do not yet have a telescope, you can still enjoy this month s deep-sky tour with binoculars, then return inspect these objects later when you are ready to use a telescope. The Hyades As mentioned in the tour of the constellation Taurus, the Hyades star cluster comprises most of the V-shaped group of stars that make up the constellation Taurus. The cluster spans a patch of sky about as large as your fist held at arm s length.

27 -27- The Hyades is what astronomers call an open star cluster, a group of relatively new stars which each formed out of a massive cloud of gas and dust and which remain held together by their mutual gravitational pull. Not every star here is part of the Hyades. Aldebaran, as you have learned, is a foreground star. But at least 20 true members of the cluster are visible here without optics in dark sky, and dozens more leap into view with binoculars. The Hyades have been known since antiquity. The cluster s name comes from the Greek legend of the seven Hyads, the daughters of the titan Atlas and Aethra. Atlas was busy because he had seven more daughters by another wife, Pleione. These daughters were called the Pleiades. So by legend, the Pleiades and the Hyades are half-sisters. The Romans called the Hyades Sidus Hyantis, the Raining Stars because legend tells the Hyads rained tears on Earth after the death of their brother Hyas. The appearance of these stars also coincided with the rainy season around the Mediterranean. The center of mass of the Hyades is just 151 light years away, which makes the The Hyades one of the closest star clusters to Earth. Astronomers have carefully measured the apparent motion of the Hyades across the sky and determined it moves away from Earth and toward a point just east of the bright star Betelgeuse. Fifty million years from now, the cluster will appear dim and small, just 0.5 degrees across. The presence of many orange-giant stars suggests the Hyades have been around for some 700 million years. That s old for an open cluster. It s likely no coincidence that the Hyades are about the same age as the Praesepe star cluster in Cancer, which you will meet next month. The two clusters have a common motion through space, and likely formed together out of the same massive cloud of gas and dust.

28 -28- The stars of the Hyades star cluster, which makes up the V of the constellation Taurus The Hyades is a splendid cluster in binoculars. Spend as much time as you can inspecting the stars here, and train your eye to see colors, patterns, and tiny groups of stars in close proximity. The presence of brilliant Aldebaran adds drama to the spectacle. There are several pairs of fine close pairs of stars in the Hyades. Without optics, see if you can resolve the pair called the Deltas in the northern branch of the V of the Hyades. There are two stars here, and a third a little further away. With average eyesight (or a pair of prescription glasses), most observers can resolve the Deltas with the unaided eye in reasonably dark sky. If the Deltas are easy, see if you can split the closer pair called the Sigmas, just 1 degree southeast of Aldebaran. And If you can split the Sigmas, try for the Kappas. These stars are north of the V (see the map above). These stars are made more challenging by their difference in brightness. If your eyes are really keen, see if you can resolve 80 and 81 Tauri. You need dark skies for these: they re just on the edge of visual detection and they are at the limit of resolution for even the sharpest eyes.

29 -29- All these pairs are easily resolved in binoculars. And if you don t have a telescope yet, don t worry. The Hyades is one of the few deep-sky objects that is too large to fit into the field of view of most telescopes. It looks far better in binoculars. The Pleiades Many a night I saw the Pleiads, rising thro the mellow shade, Glitter like a swarm of fireflies tangled in a silver braid. Tennyson Now to the Pleiades, perhaps the most famous star cluster in the heavens. This tiny dippershaped cluster lies a little further on the same line from Orion s Belt through the V of Taurus. The Pleiades is a visual delight on a cold winter s night and has been a favorite target of stargazers since antiquity. While it s not as visibly large as the Hyades, it still looks far better in binoculars than a telescope. The Pleiades are much younger than the Hyades. They formed some 100 million years ago. And they are farther than the Hyades, some 445 light years away. So the light striking your eye from the Pleiades left the year William Shakespeare was born, give or take a few decades. The Pleiades star cluster The Pleiades are often called the Seven Sisters. But most casual observers can see only six stars here without optics, although in very dark sky, some observers can see more. In binoculars, dozens more stars are visible. The nine brightest stars of the Pleiades are named for the Seven Sisters in Greek mythology, Alcyone, Maia, Asterope, Merope, Electra, Taygete, Celaeno, along with their parents Atlas and Pleione. Nearly every world culture has a name and legend for this star cluster. In Sanskrit, the cluster is called Kṛttikā, which refers to the six sisters of the god Murugan. The Japanese refer to this

30 -30- cluster as Subaru, from which the famous car company takes its name and logo. In the middle ages in Europe, the Pleiades was associated with Halloween because it reached its highest point near midnight on that date. Legend also tells of the Pleiades reaching high into the sky on a night in 1650 B.C. when the island of Santorini in Greece exploded in a volcanic eruption and destroying the Minoan civilization on a nearby island. This lost civilization has long been associated with the mythical lost continent of Atlantis. In 1859, an extensive blue-white nebula was discovered, of a broad oval form, with the star Merope immersed in one end of it. It was thought the nebula is caused by starlight reflecting off residual gas and dust left over from the formation of the cluster. But modern studies suggest the dust is simply a part of the interstellar medium through which the cluster is passing. Although the nebulosity is easily seen on time exposure images, the reader should not expect to be able to see the nebula in the Pleiades with anything other than binoculars of mm or more in aperture and pristine dark sky. There s one more difference between the Pleiades and the Hyades. Notice how the stars of the Pleiades appear mostly blue-white, while the stars of the Hyades exhibit a greater mix of color: blue, white, yellow, and even yellow orange. The difference in star color between these clusters is a direct consequence of their age. You will learn more about this how the age of a star cluster influences the colors of its constituent stars in a later lesson in this program... The Great Orion Nebula Look now for Orion s Sword, a group of three stars hanging obliquely from Orion s Belt. Look carefully at the middle star in the sword... it will appear slightly fuzzy and unfocused. This is not an illusion... this star is in fact the famous Orion Nebula. As beautiful an object as you will ever see in the night sky, the Orion Nebula is a blister of glowing hydrogen gas set alight by blazing new stars. This nebula is just a small part of the vast star-making machinery in our own Orion Arm of the Milky Way that offers many wondrous sights for backyard observers. The Orion Nebula is one of the finest sights in all of nature: the birth of a cluster of new stars out of a dark cloud of interstellar gas and dust. Astronomy writer Walter Scott Houston said of the Orion nebula, No amount of intensive gazing ever encompasses all its vivid splendor. It s truly one of the most beautiful things you will ever see.

31 -31- The Orion Nebula, M42, in the Sword of Orion Before the Pleiades and the Hyades became star clusters, they must have looked quite like the Orion Nebula. The new stars in these clusters were wrapped in a thick cocoon of gas and dust from which they formed. As the young stars turned on, they set the gas and dust aglow in hues of pink and blue. In time, the light pressure from the new stars blew away the dust and gas, and only the star cluster remained. In time, after a few more million years, the Orion Nebula itself will dissipate and an open star cluster like the Pleiades will be seen here. The Orion Nebula is often called M42, after its position in the 18th-century catalog of deep-sky objects by Charles Messier. Many brighter deep-sky objects like this nebula are classified as Messier objects. The Pleiades, for example, is M45. In binoculars, the Orion nebula appears as a grey misty patch, somewhat triangular, which overlaps with a bright star within. This star is theta Orionis. The top star in Orion s sword is NGC 1977, another star cluster wrapped in faint nebulosity. Just north of this is yet another cluster of new stars, slightly more spread out than NGC 1977, called NGC 1981, which resolves into half a dozen stars in binoculars. And just south of the Orion Nebula lies a blazing bluewhite star iota Orionis, which is the southernmost of the three stars visible in the Sword with your unaided eye.

32 -32- Note: NGC, or the New General Catalog, refers to another catalog of deep-sky objects like galaxies, nebulae, and star clusters. The Orion Nebula and region as it might appear in binoculars Turn a telescope toward M42 and you will see a greyish bat-shaped mist lit up by dozens of bluewhite stars. Try looking at the nebula with a range of magnifications. Start low, say at 40-50x, and work your way up. The nebulosity extends much farther than you may first think: use averted vision to glimpse its full expanse. At high magnification you ll lose the overall shape, but you can see the fine detail in the nebula s mottled structure and the beautiful diamond-like stars near the center that sparkle like a jar full of fireflies. Because of its size and brightness, the Orion Nebula looks almost as good from city skies as it does from country skies, and is a fine sight in small and large telescopes. In a small scope, the nebula appears greyish because its light is not bright enough to stimulate the color-sensing cone cells in your retina. At the heart of the nebula is the multiple star system theta Orionis, also called the Trapezium, so-named because it looks like a tiny trapezoid. There are actually six stars here, though you need good seeing, a 4 inch or larger telescope, and magnification of 100x or more to resolve them all. The stars of the Trapezium, which are just 100,000 years old, have blown a bubble in the surrounding gas that gives us a view of the nebula s inner core. Deeper within the nebula, unseen at visible wavelengths, lie hundreds more new stars.

33 -33- The energy that lights up the gas and dust of the Orion nebula comes from dozens of hot new stars that have recently coalesced out of the nebula itself. Hydrogen and traces of oxygen gas absorb the blue and ultraviolet light from the stars and re-radiate red and green light at characteristic wavelengths. M42 lies some 1,500 light years from Earth and spans about 20 light-years. Radio telescopes show the unlit gas and dust span more than 100 light-years beyond the visible nebula and contains the mass of 10,000 Suns. The Orion OB1 Association The Orion Nebula is a place of ongoing star formation in a huge and invisible mass of gas and dust that fills almost the entire constellation of Orion. The stars of the Orion OB1 association; Orion Nebula is pink splotch in the middle of the sword Most of the stars in the constellation were born in three waves of star formation. The Sword region is the most recent, and stars are still in the process of formation here. The Trapezium is just a hundred thousand years old, very young by astronomical standards. The oldest stars in and around the Sword are 3-6 million years old, still quite young. The stars of and around Orion s Belt were formed in an earlier wave of star formation about 8 million years ago. The oldest group of stars in Orion, a thick patch just to the west and north of Orion s belt are about 12 million years old. These associated patches of star with a common origin and age are called stellar associations.

34 -34- Each wave of star formation was triggered by supernova explosions of other massive stars which compressed the dust and gas in this part of the galaxy and began the process by which small globules of material collapse, heat up, and ignite into new stars. In time, nearly every new star the Orion association will detonate as a supernova, increasing in brightness by a hundred-fold for a few weeks before fading forever. The pressure from these explosions will trigger yet more star formation in the coming millions of years. It s all part of the ongoing ecology of our dynamic Milky Way galaxy. We see little evidence of this dynamic activity during our short lifetimes, but rest assured the Milky Way is as dynamic and restless as clouds on a stormy day. The Crab Nebula Nearly a thousand years ago, on a late-april morning in the year 1054, groggy Chinese astronomers awakened to the spectacle of a blazing new star in the daytime sky. This guest star, as they called it, appeared out of nowhere, shone with a reddish-white light some six times brighter than Venus, then slowly faded from daytime view after 23 days. What they observed was a supernova, a massive star suddenly collapsed upon itself before exploding with as much energy as an entire galaxy. European skywatchers must have observed this event also, but they were preoccupied with surviving the Dark Ages and made no record of this supernova. But the Chinese, along with their Japanese and Arabic colleagues, noted the position of this exploding star with enough precision that modern astronomers link this supernova with the Crab Nebula, a faint splatter of light easily seen in the constellation Taurus with binoculars or a small telescope. M1, the Crab Nebula, in the same field of view as zeta Tauri, as they might appear in binoculars The Crab Nebula is the first object in Messier s famous catalog, so it s commonly known as M1. It s the only supernova remnant in the catalog. In a small telescope, the nebula appears as an oval splotch about 6 x4 just one degree north-west of 3rd magnitude zeta Tauri (see map). This

35 -35- makes it easy to find. At magnitude 8.4, it s visible in 7 50 binoculars in dark sky. At 30x in a small telescope, the nebula fits in the same field of view as zeta Tauri. At higher-power, the nebula reveals a pinched off region near its centre. The delicate tendrils visible in images are visible only with difficulty in larger telescopes. The location of the Crab Nebula (upper left) near the star zeta (ζ) Tauri; the Pleiades are at left, and the V of the Hyades is bottom, middle. The exploding star that formed the Crab left behind a pulsar, a dense city-sized remnant of the stellar core that spins around once every 33 milliseconds near the center of the nebula. The pulsar is too dim to be seen with a small telescope. But astronomers have learned much about this object through observations at radio and X-ray wavelengths. Around the pulsar is a dense bubble of material bound by a strong magnetic field. Beyond that is the material ejected by the supernova itself. That s what you see with your telescope. The remnant continues to expand outward at 1500 km/s, fast enough to notice during a human lifetime. The Hubble Telescope has revealed changes in the outer shell of the Crab Nebula over a few days, which is amazing for an object that s some 6,000 light years away! The nebula takes its name from a drawing made by Lord Rosse in 1844 with a 36-inch telescope at Birr Castle in Ireland. The drawing resembles a horseshoe crab.

36 -36- Since M1 lies about 1.5 degrees off ecliptic, the Moon sometimes moves across it, which helps astronomers map the X-ray emission from the central region of the nebula. The Sun s corona also passes in front of M1 every June, and the X-rays from the nebula help astronomers infer the physical nature of the corona. Astronomers also used the space-based Chandra X-ray observatory to observe Saturn s moon Titan passing in front of the Crab. This helped determine the thickness of Titan s atmosphere. M41 in Canis Major Close-up of the Crab Nebula through the Hubble Space Telescope South and east of Orion, the constellation Canis Major is fairly rich with small clusters of bluewhite stars. The constellation frustrates observers in the northern hemisphere because never gets far above the southern horizon. But the bright star Sirius guides the way to M41, the constellation s best known and easiest-to-find star cluster. With a mix of hot blue-white stars and a few red giants, this cluster presents a range of contrasting color and brightness. In dark skies, you can see Messier 41 with the naked eye. But it looks best at low power in a modest telescope or pair of binoculars. M41 is a fairly loose open cluster. It s easy to resolve in a small telescope and spans the same area as the full Moon. To get the most pleasing view of M41, keep the magnification as low as possible. It s especially pretty in binoculars at 10x-15x. If you have a telescope ready to go, you ll see 40 or 50 stars at 25x to 40x. More stars will be revealed at higher magnification, but you ll lose the aesthetic beauty of the cluster.

37 -37- Messier 41, just south of Sirius Chances are, if you can see Sirius, you can see M41. It s just 4 degrees south of Sirius. This is a fine region for bright nearby stars. Just west of Sirius is Mirzam, a star in Canis Major which 4 million years ago far outshone Sirius as the brightest star in our sky. The location of M41 in Canis Major

38 -38- M41 contains mostly young blue-and-white stars. But near the center of the cluster, look for a contrasting deep orange red star. Within the field of view of a low-power eyepiece, you ll also see the brighter star called 12 Canis Majoris. Physically and scientifically there is nothing remarkable about M41. It s 2,300 light years away and spans some 25 light years. This cluster is of a modest age, some 100 million years old. But it s still a splendid object for binoculars and modest telescopes. M36, M37, and M38 in Auriga Your final deep-sky targets in this first month of The Art of Stargazing are the three clusters M36, M37, and M38, the showpieces of the grand constellation Auriga. These are a little trickier to find than the other deep-sky sights this month. But they are the showpieces of the Charioteer, and well worth the effort to see on a cold winter s evening. Each of these three clusters is about 4,200 light years away. But that s where the similarity ends. M37 and M38 are about the same size, but M38 resolves into individual stars much easier than the denser M37 in a small telescope or good pair of binoculars. M36 is the smallest and youngest of the trio, and, with optics, presents a lovely arrangement of blue white stars. You might fit all three clusters into the same field of view with 7x binoculars. M36 is the smallest and youngest of the trio, and, with optics, presents a lovely arrangement of blue white stars. The cluster lies within the hexagon of Auriga just northwest of the mid-point of the line between Elnath and θ (theta) Aurigae (see map). The cluster comprises a loose group of about 50 stars. Moderate magnification in a small telescope opens the cluster up nicely for inspection. The edges of the cluster are not well defined, and streams of blue stars appear to arc out from the center like the arms of a distorted cross. Look for the pair of moderately-bright stars near the center of the cluster. This is the double star Σ737. Look also for an absence of stars at the south end of the cluster. Just two degrees northwest of M36 lies M38. It forms an equilateral triangle with Elnath and ι (iota) Aurigae. The cluster is about 0.3o across, and 1/3 larger than M36, but it s also half a magnitude fainter. There appear to be twice as many stars in the cluster as M36-- about 120 stars-- and the cluster is much older than M36, so there are fewer blue-white stars here. At 75x, you ll see about stars of magnitude 8 and fainter. Like M36, the boundary of M38 cluster is ill defined. There s an odd-looking void near the center of the cluster. And there appears to emanate a ragged cross from this void, with the long arm running west-southwest to east-northeast. Higher magnification brings out more stars, perhaps total in a 4-inch scope.

39 -39- The open star cluster M37 is the brightest of the three Auriga Messier objects and by far the most striking. It lies just outside the hexagon of Auriga, about as far outside the hexagon as M36 lies within it. The cluster presents a rich spray of faint star clumped around a glorious central redorange star. M37 makes the best-of list of many experienced stargazers. For dramatic effect, look first at M36 then M38 and end with the magnificent M37. M37 in Auriga Location of the star cluster M36, M37, and M38 in the constellation Auriga While even binoculars can nearly resolve M36, M37 is far tighter and only shows its character in a telescope. M37 is much more compact than M36 or M38... the bulk of the stars lie within an apparent diameter of 1/4 of a degree. As M37 lies at the same distance as the other two clusters in Auriga, the apparent richness of the cluster is real. There are nearly 2,000 stars here all told, though you can see perhaps 200 with a 4-inch telescope. M37 is most dramatic not only for its stars, but also for its dark lanes that appear to wind through the cluster. If you are using a

40 -40- telescope, defocus it slightly to accentuate these dark regions, and relax your eye as you follow them in and around the rich field of stars. Some claim to see the outline of a spider among these stars. Solar System Observing A Brief Tour; Jupiter You ve covered a lot this month, so our look at the sights for our own solar system will be brief as we take a quick peek at the planet Jupiter. Jupiter is the brightest and most accessible planet in the sky this month, and it is the brightest object in the evening sky except for the Moon. The planet lies in the constellation Taurus, as you learned earlier in the sky tours. The planet Venus is always brighter than Jupiter, but Venus is presently lost in the Sun s glare. First, a very quick overview of our solar system. At the center, of course, is the Sun, our home star. It makes up 99.86% of the mass of the solar system. The other 0.014% is in the planets, the asteroids, comets, and so on. The solar system has eight major planets which are, in order from increasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Little Pluto, which lies beyond the orbit of Neptune, is no longer considered a major planet, but is now one of five dwarf planets. The Sun and planets of our solar system; the separation of the planets is not to scale The image above is not to scale. In fact, the planets are much farther apart from each other, and their physical dimensions are much smaller than their distances from the Sun and each other. The Earth, for example, is some 150,000,000 km from the Sun, but it is just 12,700 km in diameter. If the solar system were as large as a dinner plate, the planets would be tiny specks of sand.

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