Astronomy Club of Asheville July 2018 Sky Events

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1 July 2018 Sky Events The Planets this Month page 2 July 9 th - Conjunction of Venus and Regulus page 4 July 14 th - Crescent Moon Meets Mercury and Venus page 5 July 24 th - Moon, Saturn and a Teapot page 6 Planet Highlights page 7 Moon Phases - page 9 July 6 th - Earth Reaches Aphelion - page 10 July All Eyes on Mars page 12 July 27/28 - Delta Aquarid Meteors - page 15

2 July 2018 Sky Events the Planets July 2018 reintroduces all five bright planets to evening skies, a sight not seen for many months. Unfortunately, they aren t visible simultaneously; a few hours will be required to track down the quintet, which are spread through a three hour window in the sky. Quick moving Mercury is challenging to spot at the best of times. The solar system s innermost planet never wanders far from the Sun; the result is that seeing Mercury often means hunting through dawn or dusk twilight. Start with binoculars. Once located, keen eyes are usually able to resolve this object without visual aid. Find Mercury moving through the constellations Cancer and then Leo, low to the western horizon, about 30 minutes after sunset. After the third week in July the planet dims and quickly dives toward the Sun, lost now before reappearing in morning skies at the end of August. In contrast to elusive Mercury, extroverted Venus shouts out to all whose eyes wander upward. Shining at magnitude 4.1, this beacon glows in the west after sunset. Telescopes will reveal a waning gibbous phase, increasing in diameter (and brightness) and moving through Leo as the month progresses.

3 July 2018 Sky Events the Planets Jupiter, high overhead near the meridian as darkness falls, remains in excellent observing position this month. This dynamic gas behemoth is the King of the Skies even modest telescopes (and larger binoculars) will reveal four Galilean moons and distinctive cloud bands spread across its disk. The 2.2 magnitude planet is found meandering through Libra in July. Saturn is now the property of evening skies, having reached opposition its closest approach of the year at the end of June. Rising in the E-SE just after sunset and found directly above the teapot s lid in Sagittarius, it approaches the meridian near midnight. July is still a fantastic month to enjoy Saturn s ring system; their northern face remains tilted near their maximum extant (26 ) toward the Earth. While Jupiter may be the King of the Skies, July offers up some serious competition Mars to Jupiter s throne. This month the Red Planet makes its nearest approach to the Earth since 2003 (see page 12). Not until 2035 will Mars be as large or bright in our skies. While the five bright planets grace evening skies, much dimmer Uranus and Neptune are relegated to morning duty. Located in the water constellations of Pisces and Aquarius, respectively, both can be observed before sunrise in July.

4 July 2018 Sky Events the Planets Conjunction of Venus and Regulus On the evening of Monday, July 9 th, catch an appealing conjunction of the star Regulus and a much brighter object the planet Venus separated by 1 degree. Look to the west about 9:30 p.m. EDT to locate this pretty duo. Regulus, the alpha star in the constellation Leo, forms the end of its famous sickle asterism (also known as an inverted question mark ) and is about 77 light years distant. Compare this to Venus relatively close position at only 92 million miles! Image courtesy of Sky & Telescope A multiple star system, Regulus is an optical binary star. Try your luck splitting this close pair with binoculars while also enjoying brilliant Venus. And with binoculars in hand, don t forget to attempt spotting Mercury, partially hidden by twilight s glow on the western horizon.

5 July 2018 Sky Events the Planets A Crescent Moon Meets Mercury and Venus On the evening of Saturday, July 14 th, a thin crescent Moon accompanies Mercury in the fading glow of sunset. On the following night, Sunday the 15 th, Venus shines with its own crescent lunar companion. On Saturday, around 9:30 p.m. EDT with an unobstructed view low to the western horizon, try your luck detecting the crescent Moon. Use this lunar guidepost to spot elusive Mercury just below. The task will benefit greatly from the aid of binoculars. Sunday evening s pairing of brilliant Venus and a larger crescent Moon will be much less challenging, requiring no optical aid other than your keen eyes! Image courtesy of Sky & Telescope

6 July 2018 Sky Events the Planets The Moon, Saturn and a Teapot On the evening of Tuesday, July 24 th, the waxing gibbous Moon accompanies the planet Saturn, separated by about 2 degrees and found in the constellation Sagittarius, the Archer. Situated in the south-southwest, above Sagittarius well-known teapot asterism, these two celestial objects appear close in our 2-dimensional view. Saturn is, however, positioned some 851 million miles behind the Moon. While reflected sunlight from the Moon reaches the Earth in just over one second, Saturn is some 76 light-minutes distant! Image courtesy of Sky & Telescope

7 July 2018 Planet Highlights Chart courtesy of Sky & Telescope

8 July 2018 Planet Highlights Movement of the Sun, Moon and Planets this month Chart courtesy of Sky & Telescope

9 Moon Highlights July 2018 ** ** The Thunder Moon Times shown are in Universal Time (UT) subtract 4 hours to convert to EDT Illustration and info courtesy of Sky & Telescope

10 July 6 th Astronomy Club of Asheville July 2018 Sky Events - Earth Reaches Aphelion Earth reaches aphelion the farthest position from the Sun in its annual elliptical orbit. Distances in miles: Aphelion 94.5 million Perihelion 91.5 million Average 93 million or 1 astronomical unit (AU) ~ the Earth-Sun distance < Sun Earth > There is a 3.3% change in the distance from aphelion to perihelion. Not to scale

11 July 6 th Astronomy Club of Asheville July 2018 Sky Events - Earth Reaches Aphelion On July 6 th this year you may notice that you are orbiting on planet Earth slower than usual! Here s why: Kepler s 2 nd Law of Planetary Motion states that an imaginary line joining a planet and the Sun sweeps out an equal area of space in equal amounts of time. Perihelion Aphelion Not to scale As determined by Kepler s 2 nd Law of Planetary Motion, the speed of a planet along its elliptical orbit is fastest when it is closest to the Sun (perihelion) and slowest when it is farthest from the Sun (aphelion).

12 July 2018 Sky Events All Eyes On MARS The Red Planet s Closest Approach for 32 Years Avid skywatchers have had an appointment with July 2018 for years. Not since 2003 have the planet Mars and the Earth been positioned so closely together an occurrence not repeated until 2035 making this summer s Mars a must-see-tv (telescopic-views) event! Images courtesy of Sky & Telescope Big changes in Mars apparent size as it approaches, and then recedes, from the Earth, providing detailed views of surface features such as its southern white polar cap (shown at top in these images). The planet makes its closest approach on the night/morning of July 30-31, when it lies just 35.8 million miles away. Mars won t be difficult to find; the rusty planet peaks at magnitude 2.8, rivaling Jupiter at its brightest, and even outshines our sky s brightest star Sirius (magnitude 1.4) from June through September.

13 July 2018 Sky Events All Eyes On MARS The Red Planet s Closest Approach for 32 Years Why does this distance from Earth vary so greatly? The reason is the Red Planet s highly elliptical orbit and how the two planets align at their closest points (called opposition), about once every 26 months. Opposition March 2012 Opposition July 2018 When opposition occurs at or near Mars perihelion (the nearest point to the Sun in its orbit), observers are blessed with a fine close apparition million km (62.6 million mi) million km (35.8 million mi) diagram not to scale In contrast, oppositions which coincide with Mars at aphelion (its farthest point from the Sun) provide shrunken telescopic views of the ruddy world, with few decipherable planetary details. In 2018, Mars is at opposition with the Earth on July 27 th ; it reaches perihelion on September 16 th.

14 July 2018 Sky Events All Eyes On MARS The Red Planet s Closest Approach for 32 Years Locate Mars in the constellation Capricornus, rising in the E-SE around 11:00 p.m. as July begins; Mars makes its entrance just after 9:00 p.m. by month s end. True color image of Mars, taken by the Rosetta spacecraft in 2007 Along with the excitement of a close peek at Mars, however, there is bad news the planet s southern trajectory through the ecliptic remains low in our skies, and sharp telescopic views will likely be compromised by Earth s thicker atmosphere near the horizon. Just when you re yearning for perfect atmospheric seeing to discern fine details, unsteady, turbulent air could spoil your enthusiasm! To improve your chances of capturing an unforgettable view, try when Mars is at its highest and near the meridian meaning well after midnight and observe over multiple nights for two (or more) weeks before and after the July 31 st closest approach. Mars was the Roman god of war. This summer a battle will wage to capture a glorious view of the Red Planet before it recedes to more humble flanks in our skies elude the engaging action at your own peril

15 July 2018 Sky Events Delta Aquarid Meteor Shower The Delta Aquarid Meteor Shower peaks in late July, with estimates of meteors per hour. These meteors tend to be faint. The peak night for 2018 is predicted to be Saturday, July 28 th and into the early morning hours of Sunday, July 29 th. The meteors, however, should be visible for a few weeks on either side of the estimated peak dates, appearing to radiate from the direction of the Delta star (called Skat) in the constellation Aquarius hence their name. Look for these meteors between midnight and dawn, and an unobstructed view of the sky at a dark location will increase your observing success. Unfortunately, in 2018 the shower s peak night coincides with a Moon just past its full phase, assuring that bright moonlight will interfere with all but the brightest meteors!

16 July 2018 Sky Events Delta Aquarid Meteor Shower The view about 1:00 a.m. local time on July 29 th. The Delta Aquarid meteors will appear to radiate from this area of the sky.

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