Observation of the Spring Night Sky Self-Guided Viewing Program

Transcription

1 Observation of the Spring Night Sky Self-Guided Viewing Program Physics 406, Homework #2, due February 23 Term Paper by Howard C. Murphy Physics 406 University of New Hampshire Fall 1998 edited by E. Möbius, January 2004

2 Introduction to the Spring Night Sky No course in astronomy is complete, if you never take the time to actually look at the night sky. When you learn to find your way around the sky, lessons learned in the classroom take on an added dimension. The sheer enormity of space and the objects it contains becomes real when you actually go outside and just look at the enormous wealth of objects. For example, take Jupiter, it is almost a dozen times as big across as Earth, and never less than five times as far from the sun as our planet. Then turn a little to look at Betelgeuse, the red star in Orion s right shoulder, an object so big that if it were our own sun, Jupiter would be inside it. Knowing the sky provides us with not only a sense of scale, but of place. The daily motions of sun and stars can be conceptualized as the heliocentric theory, but when students observe with purpose and then measure these motions, the theory becomes real. The key to astronomy is the sky itself. This exercise involves a kind of self-guided tour of the heavens. It contains a complete set of star maps for a typical observation time in the Spring Semester. We have compiled a set of maps for the evening of February 10, which shows the night sky, as it will appear at 8:00 PM. It is contained in this Homework. The primary objective of this exercise is to help you to learn the sky, not everything of course, but at least the major constellations, their brightest stars, and the planets that are visible at this time. It s an introduction to the sky. You won t be able to really see it all in one night. Multiple observations will help you to remember what you have seen and to look more deeply into what you already know. The charts are good for about two weeks on either side of the date printed on the charts and, for an hour or so on each side of the time. Here s why. The stars appear at the same place in the sky once a year, that is, they appear to move once around the celestial sphere (360 o ) in three hundred sixty-five days. That s about a degree per day. The sky pattern advances from east to west one degree every four minutes so, in an hour it moves fifteen degrees - about two weeks worth of motion, if viewed at exactly the same time of the night. Going out to observe for the first time is fun, but a few hints might help you to enjoy the experience a bit more. First, sky-watching really is definitely better when you re with others. Helping others when you see something and receiving help from others when you re stuck keeps you looking longer - and, it s the way science is done. If you can get a car full, and you have a car to fill it s also a good idea to get out where the skies are clear, light pollution-free, and with a clear view to as much of the horizon as you can manage. Don t trespass. The university owns a lot of land around here. You don t need any special observing aids, although a pair of small binoculars will help you to see some things, like the color of stars, more clearly and they re easy to carry. If there s a moon out, look at it with your binoculars. Lunar geography is fun to learn if you feel like it later. 2

3 Introduction to the Spring Night Sky Also, pack lightly, but pack a few things that will be handy. Dress appropriately and make sure you can stay warm. Bring a candy bar or something else to snack on. Don t litter. A thermos of warm coffee or tea will be appreciated if you re out for a while. You ll definitely be out for a while; you can t do this right in fifteen minutes. Bring a small flashlight with you, but don t use it liberally. Better still, if you can find a piece of red cellophane to place over the lens it will help prevent your eyes from having to completely readjust to the dark every time you use the light to refer to your chart. If you need to refer to the manual frequently, it may be a good thing to take turns being primary spotter and prompter. Once something is found, all should be in agreement that the object in question is what people believe it to be. The set of charts is accompanied by a checklist, which you can use to keep track of the major stars and constellations you have located. Because you have two charts for each viewing direction, each with different information, you may want to sacrifice one of the charts by cutting it out to paste onto the other to keep track of those objects you have located. One of the charts helps to guide your to locate objects by also including connecting lines for the brightest stars in the major constellations. It also includes parallels (every 10 o ) and lines of the same right ascension (every 15 o ). The second chart shows the sky as is, without these crutches. On the charts the names of all major constellations are shown in Bold Face type. The names of the brightest stars are given in plain type. The name mostly starts to the right of the star. In a few cases, where the stars are at the right edge of the chart the name is to the left of the star. Planets are marked in Bold Face Italics, and nebulae or star clusters in Italics. The Moon Be aware of the phase of the moon. The full moon lights up the sky so much that stargazing suffers. Crescent moons and new moons make for good stargazing. About one week either side of the core date used of the star charts are really good to watch stars. However, we want you to also look at the moon and its phases. Go out for moon watching starting immediately this weekend (January 23 25) shortly after sunset. You will be able to follow day by day how the waxing moon is changing and where it is in the sky. Around February 4 is the time when it is close to full moon. Watch again, but don t expect too much in terms of stars etc. Around February 8 you will still see the moon rising, when you stay up later. Right after you receive this homework and after February 8 are the best times to see most of the stars. However, don t procrastinate and wait until after February 8! Bad weather may be persistent at inconvenient times. Take advantage of good weather as soon as it is there! If you wait too long, you may be clouded in, and then I don t give you any extra time! You have four weeks to do this observation. Enjoy your sky watching! 3

4 Introduction to the Spring Night Sky How to get credit for this Homework? Fill out the Checklist and answer the questions concerning your observation day, as shown in the template that follows the checklist. Note: To measure the Altitude of Mars (in the western sky) and Regulus (in Leo) above the Horizon use your fist as a protractor. Remember your extended fist is 10 degrees wide. The accuracy that you achieve in this way is sufficient for this Homework. Due Date for this homework set: Monday, February 23 However, if you do this already before the first Exam, it will help you greatly to be prepared! Remember: The view changes slightly over time. Don t put this observation off for the last week! To observe the moon you have to go out several times! Hint: You will see Saturn and Regulus above the horizon for the entire time until the due date. However, Saturn will very slowly move among the stars. So look for Saturn in the neighborhood where it is shown in the chart, if you are not observing close to the February 10, to get your bearings. As a planet, Saturn will shine steadily (with a yellowish tint) as opposed to the stars, which twinkle all the time 4

5 Name: _ North Ursa Major Dubhe Merak Alioth Mizar/Alcor Alkaid Phad Ursa Minor Polaris Kochab Cassiopeia Caph Schedir gamma Cassiopei Ruchbah Cepheus Alderamin delta Cephei East Leo Regulus Algieba Checklist and Questions Spring Sky Checklist 2/10/2004 Ras Elased Australis Zosma Denebola Hydra Alphard Cancer Jupiter South Orion Mintaka Alnilam Alnitak Rigel Betelgeuse Bellatrix Orion Nebula Canis Major Sirius Mirzam Wesen Adhara Aludra Canis Minor Procyon West Pegasus Algenib Markab Scheat Enif Andromeda Alpheratz Mirach M31 Triangulum Aries Hamal Sheratan Cetus Menkar Mira Mars Venus Student ID: Zenith Auriga Alnath Capella Menkalinan Perseus Algol Mirfak Atik Taurus Aldebaran Pleiades Alcyone Gemini Castor Pollux Alhena Saturn Check each object you have observed with a checkmark. If you are not sure about your observation of an object, put in a question mark. This does not count against you. Objects with many question marks probably will need an improved description. I would like to get this information! 5

6 Checklist and Questions Date of Observation Observation Time Weather Conditions Moon visible not visible? If visible: Phase of the Moon _ Seen in which direction? _ Regulus: Seen in which direction? _ At which Altitude _ Mars: Seen in which direction? _ At which Altitude _ Moon observation: (Late January) Date of Observation Observation Time Phase of the Moon _ Seen in which direction? _ Moon observation: (around February 4) Date of Observation Observation Time Phase of the Moon _ Seen in which direction? _ If you want to take a second opportunity for stargazing, please record it in the same way: Date of Observation Observation Time Weather Conditions Moon visible not visible? If visible: Phase of the Moon _ Seen in which direction? _ Regulus: Seen in which direction? _ At which Altitude _ Mars: Seen in which direction? _ At which Altitude _ Correct answers to the questions: 6 points for all At least 50% of the objects checked off (checkmark or?): 8 points 2 Moon Observations: 6 points 20 Points Total If you go a second time, answer all questions and have checked off at least 75% of the objects: up to 10 extra points Due Date: Monday, February 23 6

7 Northern Skychart 2/10/2004 The key to the northern sky is the Big Dipper, an asterism, found in the constellation Ursa Major. An asterism is a pattern of stars, which, although it does not constitute an entire constellation, is nevertheless readily recognizable. The Big Dipper is among the most familiar groupings of stars in the northern sky. Look for it in northeastern direction, where it stretches upward in the sky at this time. It consists of four fairly bright stars forming the cup part of the dipper, and another three stars, which form the handle of the dipper. It s big and takes up a fair part of the sky. Note from the diagram that the cup points upward and is open to the left. The handle of the dipper contains three bright stars: Alioth, Mizar, and Alkaid. Of these three, the central star, Mizar, is worthy of some remark. Mizar is accompanied by a companion star, Alcor. The two are very close together, so close that they appear at first look to be a single star. However, if your eyesight is very good and your skies are clear and dark, you may be able to resolve Mizar/Alcor into two stars. If not, a pair of binoculars will do it easily. The dipper contains two bright stars that run horizontally along the upper edge of the dipper s cup, Dubhe and Merak which are commonly called the pointers. Phad is the bright star in the lower right corner of the dipper. Because two points determine a straight line, if you allow your gaze to move along the imaginary line determined by Merak and Dubhe towards the left, the next bright star you encounter is Polaris, the North Star. This star, which is similar in brightness to the pointers, is the brightest star in Ursa Minor, a constellation that also contains an asterism, the Little Dipper. Polaris is the last star in the Little Dipper s handle. Kochab is the brightest star in the cup of the Little Dipper. The Little Dipper is less imposing than the Big Dipper, because it is not only smaller, but contains fainter stars. Unless you have a good, dark observing site, it may be difficult to see. If you can t make it out clearly, you may consider trying to find a darker observing site. It really is worthwhile finding the best observing site you can. It s easiest to learn the your way around the sky when you can actually see what you re looking for. Ursa Major and Ursa Minor are two of the circumpolar constellations. Circumpolar constellations are always entirely in the sky, that is, above the horizon, even during the daytime. Cassiopeia is another circumpolar constellation. As you stand looking directly at Polaris, picture the sky around it as a huge clock, with Polaris at the exact center of the clock in the place where the moving hands are attached to the drive mechanism. The Big Dipper is around three or four o clock. Diagonally across the clock at about nine to ten o clock is Cassiopeia. The brightest stars in Cassiopeia, Schedir and Caph are about the same brightness as the brightest stars in the Big Dipper. Seen from the right angle, they resemble a W or sometimes an M. If you cock your head a little it may be a little easier to recognize it. Cassiopeia is the brightest group of stars in its area of the sky. See if you can recognize gamma Cassiopei, the bright star between Ruchbah and Schedir. Cepheus is another circumpolar constellation. It lies next to Cassiopeia, between eight and nine o clock. Although it is intended to be a king on his throne, it also resembles a house with a big triangular roof. Go back to the pointers and retrace the line to Polaris. Continue along the line past Polaris and the next brightest star is the peak of the triangle that forms the roof of the house. The bottom two stars and two others of similar brightness further on form the main body of the house. Find Alderamin, the bright star at the base of the house, in the lower right corner as seen tonight. Delta Cephei, the star forms the upper right corner of the house s foundation. It is among the most important stars in the sky to astronomers. Delta Cephei is the prototypical Cepheid variable star. Variable stars are a kind of star whose luminosity changes over time. That is, they have a regular cycle of brightening and dimming. The time it takes to go through a complete cycle is called the star s period. Some stars brighten and dim because they are eclipsed by a companion which, in its orbit, regularly passes between us and the variable star. Others vary in their light output all by themselves. The Cepheids are of the latter variety. The variable stars, which are like delta Cephei, are valuable to 7

8 Northern Skychart 2/10/2004 astronomers because the length of time their period of brightening and dimming takes is directly proportional to both their apparent and their absolute magnitudes. This is important because once Cepheid variables have been found, they help to serve as distance measuring tools. These stars give information about the distance to stars for which parallax angles are too small to measure. Because Cepheus is circumpolar, like the other circumpolar constellations, it revolves around the pole star once a day and, if observed at the same time every night, will move once around the heavens in a year. If you observe this portion of the sky later at night or in the pre-dawn hours all of the circumpolar constellations will appear to have moved around the clock. Before moving on, be sure that you can locate Ursa Major, Ursa Minor, Cassiopeia, and Cepheus. 8

9 Northern Skychart 2/10/2004 Delta Cephei 2/10/2004 9

10 Northern Skychart 2/10/2004 2/10/

11 Eastern Skychart 2/10/2004 Let us start with a constellation familiar from our start with the northern sky, the Big Dipper. It is found in the northwestern part of the sky. If you trace the straight line along Dubhe and Merak backwards, away from Polaris, you will encounter the constellation Leo, the lion, almost exactly in the east. Its brightest star is Regulus, the front paw of the lion. Leo is filled with bright stars. To the left of Regulus and slightly higher in the sky is Algieba, which is located at the base of the lion s mane. Follow the curve of the mane up and then right until you can locate Ras Elased Australis, the last star of the curve. Now, using Algieba as a starting point, move down and left to Zosma, which lies at the base of Leo s tail. Denebola, which means tail of the lion, is down, close to the horizon. Mentally step back to see Leo as a whole. Extending a straight line from Algieba to Regulus two times beyond Regulus and then going slightly up and right we encounter Alphard, which is the brightest star in Hydra. Some of Hydra is below the horizon. Between Leo s head and the Hydra s head and lying above both in the sky is the zodiacal constellation, Cancer. Cancer does not have any bright stars and is difficult to make out. From Cancer look up and to the right (south) for Canis Minor, which contains the bright star, Procyon and its lesser companion, Gomeisa. In the evening hours you find majestic Jupiter with its bright and steady yellowish glare rising in the East. You can see it late January rising after 830 PM, then earlier and earlier. Jupiter will be climbing higher and higher over the course of the month. You find it approx. 20 o below Regulus in Leo and slightly off to the left (when looking East). You can t miss Jupiter, because it is the brightest object in this part of the sky, when it is up. And it doesn t twinkle. 11

12 Eastern Skychart 2/10/

13 Eastern Skychart 2/10/

14 Southern Skychart 2/10/2004 Seemingly the most interesting part of the sky is in the south right now. Some of the most outstandingly beautiful, and recognizable constellations in the northern hemisphere of the sky are here. Taurus, for example, is very high in the southern sky. (Taurus will be discussed in the zenith skychart.) Looking due south, you simply cannot miss mighty Orion, the hunter. This constellation is truly majestic and filled with bright stars and recognizable patterns, as well as one of the most beautiful deep sky objects, the Orion Nebula. The great hero is marked by three stars: Alnitak, Alnilam, and Mintaka, which form the belt. Alnitak is left and lowest; Mintaka is on the right and uppermost of the three. Above Mintaka and slightly to the right is Bellatrix, Orion s left shoulder. His right shoulder is Betelgeuse, a red giant star so big that if it were in our solar system, the planet Jupiter, which is over seven hundred seventy million miles from the sun, would be inside Betelgeuse. That s a red giant! Below the belt lie two other bright stars, Rigel and Saiph, which mark the feet. Of the two, Rigel is by far the brighter. Just below Alnitak is a fuzzy area that houses the Orion Nebula, a birthplace of new stars. Binoculars will bring this easily spotted area into view. Note that you see this area only in black and white, not in the beautiful colors you see in posters and films of nebulae. This is because you cannot receive enough light, even through a telescope, to excite those parts of your eyes that respond to color. Black, white, and gray are all you can see in dim light conditions. Telescopes can gather and store light on film. Over time enough light can be gathered to expose colored film. Your eyes were not designed for stargazing. They need to be able to see in the daytime and to register motion. That is, they need to receive and then dump images rapidly. Time exposures are not our eyes strong suit. From Orion, look down and to the left to see the brightest star in the night sky. Sirius, the dog star is the brightest star in Canis Major, the big dog. Look right for Mirzam, Canis Major s forepaw. Its hindquarters are made from three stars of similar brightness, Wesen, Adhara, and Aludra. From Sirius, look up and to the left for another bright star, Procyon, in Canis Minor, the small dog. Above Procyon and to the right is another, fainter star. That s about it for Canis Minor. 14

15 Southern Skychart 2/10/2004 Saturn Orion Nebula 15

16 Southern Skychart 2/10/2004 Saturn Orion Nebula 16

17 Western Skychart 2/10/2004 In the western sky about north of west is the Great Square of Pegasus. It is low on the western horizon and diamond shaped. The diamond is oriented, so that Markab is in the home plate position. Follow the bases from Markab to Scheat to Alpheratz, which occupies second base and begins the ascent into Andromeda. Above Alpheratz are two stars, slightly separated. The lower and leftmost of the pair is also the brighter of the two. Above this pair is another, slightly more separated pair, almost horizontal in the sky. Mirach is the leftmost. Move to its companion on the right and then to the right again and, if you can see a fuzzy blotch of skies, take out your binoculars and look more closely. It s M31, otherwise known as the Great Nebula in Andromeda. This galaxy, almost a twin of the Milky Way, is the one northern sky object. The final significant star in Andromeda is Almach, which make up the leftmost of a pair of stars extending up from Mirach. Almach is about half way between Mirach and Algol, which is in Perseus. If you have found Almach and Mirach, look left and you will find Triangulum, the constellation, which consists of three fairly bright stars. It seems to be pointing down towards the western horizon. It's easy to locate. Find the tip of the long skinny Triangulum and look left again for the two prominent stars, Hamal and Sheratan, the brightest stars in Aries, the ram. Of the two stars, Sheratan is the lower in the sky. Two animal constellations remain. Cetus, the whale is an enormous constellation in the southwestern sky. It is entirely above the horizon, but just barely. Cetus seems to be diving below ground, head first. The rest of the whale s body and tail extend high into the southwestern sky. This constellation really does look like a whale. Look for bright Menkar in the left part of the four stars, which make up the tail. 15 o below Menkar slightly to the right is Mira, an enigmatic variable star that changes brightness sometimes in a very unpredictable way. At this time of the year Mars can be seen prominently in the western sky. You find it looking west, to the left of Andromeda, or approx. halfway between the Pleiades (described with the Zenith chart) and the horizon. Mars will be coming closer to the horizon over the four weeks. You won t miss Mars, because it is the brightest object in this region of the sky (except when Venus is visible close to the horizon) and it is shining steadily with a reddish tint. If watch earlier in the evening or during the second half of the four week period, you can also see Venus very close to the western horizon. 17

18 Western Skychart 2/10/2004 Cetus Sheratan M31 18

19 Western Skychart 2/10/2004 Cetus Sheratan 19

20 Zenith Skychart 2/10/2004 The point in space, which is directly overhead, is called the zenith. It s the top of the starry dome. All you have to be willing to do is crane your neck a bit and you can see it all. Unless you re standing in a forest, you should be able to see pretty much everything the map reveals. The maps of the four directions along the horizon can be read like normal maps, that is, while looking north, west is on the left and east is on the right. This is not true for the zenith skymap. Look towards the north on the map, towards the circumpolar constellations. The date and time legend is on the northern side of the map, near Ursa Major, a circumpolar constellation. Next to it is Camelopardalis and Cassiopeia. As you look up at Cassiopeia, the M configuration is clearly visible. That s north all right. So, as you look at the skychart with the legend in the bottom right corner, south is at the top of the page. Imagine a map of the United States and you are standing on, say, Iowa looking south at Louisiana. West would be on your right and east on your left. On this map, however, east is on the right and west is on the left. That s because this map is meant to picture things, which are overhead. If you hold it over your head and look up at it, then as you look south east is on the left and west is on the right. This can get a little tiring, so it may be easier to hold it normally and just remember that east and west are backwards. Find Polaris, the north star. Turn completely around and look south. You are oriented to the map. Now, look straight up. You ll start at the top. Directly overhead is a bright star, Capella, the brightest star in Auriga, the charioteer. This constellation does not particularly look like a man, not in the way that Orion or even Hercules does. To the left of Capella is Menkalinan, its less luminous companion. See if you can trace the outline of the constellation. To the west, are two bright stars- Algol and Mirfak the two brightest stars in Perseus. South of these two is the constellation Taurus, the bull. Taurus is marked by the bright red star, Aldebaran and a small cluster of stars known as the Pleiades. Also the planet Saturn is here, between Aldebaran and the Pleiades, actually closer to Aldebaran. To the right of the Pleiades is Aries, the ram. You will recall from the western skychart that Hamal and Sheratan are the two bright stars in this zodiacal sign. If you move back eastwards, through Perseus, back towards the zenith and Capella, and then southeast, you can re-encounter Gemini and the bright stars, Castor and then Pollux. Look for dimmer Alhena, Pollux s left foot. Currently, the sky overhead features one of the giant planets: Saturn. It stands out by its very steady glare without twinkling and provides additional glory to this part, already full of interesting constellations. Saturn is found at the foot end of the constellation Gemini, about halfway between Castor and Betelgeuze. 20

21 Zenith Skychart 2/10/

22 Zenith Skychart 2/10/