D e s e r t E x p o s u r e 
October 2005
D e s e r t E x p o s u r e |
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 Constellation of the Month: Lyra, The Lyre Lyra, the lyre, belonged to Orpheus, son of Apollo and the muse Calliope. Apollo gave the lyre to Orpheus when he was young and he learned to play it so well that he could charm people, animals and even rocks with the sweet sounds. When he grew up, he fell in love with the nymph Eurydice and they were married. One day while Eurydice was walking through a field, a shepherd fell in love with her and began chasing her through the field. A snake hiding in the grass bit and killed her, sending her to the Underworld. Orpheus was heartbroken and journeyed to the Underworld to plead for her life. He played his lyre for Pluto and Persephone, and they were convinced to let Eurydice return to earth. Pluto warned Orpheus not to turn around and look at Eurydice or he would lose her again. Orpheus walked out of the Underworld trusting Eurydice was following. Fearing she was having trouble making the last few steps, though, Orpheus turned around and Eurydice immediately started slipping back into the Underworld, dying a second time.
Orpheus was so crushed that he forsook the company of women. The women of Thrace felt slighted by Orpheus' actions and they began throwing stones at him. At first, the stones heard his music and fell at his feet, but the women's angry cries drowned out his music, and their stones killed him. Orpheus returned permanently to the Underworld and his beloved Eurydice. Jupiter himself placed Orpheus' lyre among the stars. Lyra is easy to find in the sky as it contains the second-brightest star in the northern hemisphere, Vega at magnitude 0.2. Vega is also the westernmost star in the Summer Triangle asterism. Vega is a white star, only 26 light-years away from us. The other star of note in Lyra is the famous Double Double (technically, Epsilon Lyrae). This star, when seen in a telescope, is really composed of four visible stars that form two close pairs. The northern pair, called Epsilon 1 Lyrae, is composed of two white stars at magnitude 4.6 and 6.3 only 2.8 seconds of arc apart. The southern pair, called Epsilon 2 Lyrae, is also two white stars, but more evenly matched at magnitude 4.9 and 5.2, about 2.9 seconds of arc apart. Each star orbits the common center of gravity of it and its nearby partner, and the two pairs orbit the common center of gravity of the whole system. This is similar to the double-ended Ferris wheels you sometimes see at amusement parks. The most interesting object in Lyra is the Ring Nebula, M57. This object is actually an empty cylinder that we are looking at end-on, making M57 appear as a ring. If you look for it in a telescope, you will be looking for a tiny object, just 1.2 minutes of arc across, a little smaller than two apparent Jupiter diameters. Because of its small size, M57 is called a planetary nebula, more the apparent size of a planet in our sky than the huge nebulae that litter the Milky Way. The Ring is 2,300 light-years away and almost a light-year across. The Ring formed about 7,000 years ago when the aging 14.7-magnitude star at the center of the Ring shed its outer atmosphere into space. This is a common occurrence when a star like our Sun begins to show its age. Changes in the core of the star cause it to expand, pushing the outer atmosphere outward. While the atmosphere nearer the star is trapped by the star's gravity, the outer atmosphere is free to continue outward, forming a planetary nebula, like the Ring.
The Planets for October 2005 While Jupiter is now too near the Sun for observing in the evening, little Mercury pops up and hangs around very low on our western horizon just after sunset. This will be a poor apparition, with Mercury not actually reaching its farthest distance from the Sun until next month. You might be able to glimpse Mercury low on the west-southwestern horizon shortly after sunset. Mercury will be magnitude -0.2 at month's end, and will be about 6 seconds-of-arc across. Venus is a little higher up in the southwestern sky all month. Venus will remain about the same altitude throughout October. On Sunday night, Oct. 16, Venus will be 1.3 degrees from the bright star Antares. Venus is becoming more of a crescent as it comes closer to the Earth and appears bigger through a telescope. It shines at magnitude -4.3. Mars rises in the east about 8 p.m., and remains visible the rest of the night. It is moving from Taurus back into Aries during the month. Mars will reach its closest point to the Earth on Saturday, Oct. 29, around 9 p.m. It will glow a reddish magnitude -2.2 as it rises in the east-northeast. Telescopically, it will be about the same size as Venus, 20.2 seconds of arc across. The best time to observe Mars is around midnight, when it is highest in the sky. This is a great time to take a look at Mars through a telescope, and take a look at the dark markings as they parade past. Mars turns at almost the same rate as the Earth (once per 24 hours), so you will see the same features each night at about the same time. Saturn comes up around 2 a.m. It remains in Cancer this month, moving very slowly eastward. Saturn's ball is 17.7 seconds of arc across, while the rings are 40.2 seconds of arc across with the southern face tipped toward us at an angle of 20 degrees. There is an annular solar eclipse across Africa on Oct. 3, and the Moon will be slightly eclipsed as it is setting low in the southwest on the morning of Oct. 17. The eclipse starts at 3:51 a.m. (penumbral phase) and 5:34 a.m. (umbral phase). Mid-eclipse is 6:03 a.m., and umbral eclipse ends at 6:32 a.m., just after which the Moon will set. So take a look as you get ready for work that morning and "keep watching the sky"!
Watch the Skies (all times MDT)
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