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Astronomy From Your Back Yard - 9/15 to 9/21 2010

By Dave Grosvold

This week, the Moon is just past First Quarter, and shines to the left of the handle of the Sagittarius Teapot on Friday evening. Watch over the course of the next week, and you can observe the waxing gibbous Moon appear farther eastward in the sky at the same time each night.

This is a good time to view most of the planets in the Solar System. On Friday and Saturday evenings, Uranus will come within 0.8° of Jupiter. Uranus is easily visible in binoculars at magnitude 5.7, just to the north of mighty Jupiter, who is nearly 3,000 times brighter at magnitude –2.9. In binoculars or a small telescope with a low-power eyepiece, Pale-green Uranus appears about as bright as one of Jupiter's four Galilean Moons. Mercury is should be clearly visible low in the east about 45 to 30 minutes before sunrise all this week. It's easy to confuse Mercury with Regulus in the dim light of dawn. Regulus lies almost directly above it at the base of the Sickle of Leo.

Venus is now setting in the west before dark, and Mars is about 6° to the right, just above her. Mars is almost lost in the glow of sunset, so you may need binoculars to get a good view.

Jupiter reaches opposition on the night of Monday, the 20th. Opposition occurs when Jupiter is directly opposite the Sun in the sky as seen from Earth. Rising just after dusk in the east southeast, Jupiter is the brightest object in the sky after Venus sets. This year at opposition, Jupiter will be closer to Earth than at any other time from 1963 to 2022, and even though it's only about 1% to 2% larger than the preceding and following oppositions, Jupiter now appears nearly 49 arc-seconds wide. With the South Equatorial Belt still nearly invisible, the Great Red Spot is easy to identify in a small telescope.

Saturn is now completely lost in the glow of sunset, and won't be visible again until late October, when it appears in the eastern sky at early dawn.

Neptune, at magnitude 7.8, is visible in east-southeast about an hour after dark, and lies between the constellations of Capricornus and Aquarius. You can pick it out from a good dark-sky site, and a telescope will reveal it's pale, blueish-tinged disk.

Did you know about the supposedly “secret” US spaceplane? X-37B, the unmanned successor to the space shuttle, launched from Florida in April 2010 and began its first mission with very little public notice – because no one knew where it was going or what it was doing. The spaceplane was shrouded in operational secrecy. However, civilian specialists reported that it might go on mysterious errands for as long as nine months before touching down again.

Even though the X-37B mission was — and remains — secret, amateur astronomers first identified it after observing the object and determining it was orbiting the Earth once every 90 minutes at an inclination of 39.99 degrees. They then shared their findings with other amateurs, who have confirmed their observations and helped determine that the object was indeed the X-37B.

If the weather allows, you can catch the X-37B as it passes overhead every night this week. The X-37B does not reach anywhere near the brightness of Iridium Flares or even the International Space Station (ISS), but with magnitudes between 5.5 and 2.2, you can spot it if the conditions are right. The brightest passes occur on Saturday and Sunday evenings at magnitude 2.2 and 2.3 respectively. Look for it to pass high at altitude 85° in the south-southwest on Saturday evening at 8:35 PM CDT. Look again on Sunday evening at 7:51 PM CDT, only this time it will be at altitude 78° in the north-northeast.

For comparison, the following stars are very close to magnitude 2.2 in brightness: Denebola in Leo (Beta Leonis,) Almach in Andromeda (Gamma Andromedae,) and Mizar A in Ursa Major (Zeta Ursa Majoris.)

The ISS makes one pass overhead this week, at magnitude -0.8. Look for it to pass low in the southwest at 7:50 PM CDT on Friday, the 17th. There will also be several very bright (magnitude -8.0) Iridium Flares visible right at dusk this Thursday, Friday and Saturday. Check out the specific times and celestial coordinates for the X-37B, ISS, and Iridium Flares at the Heavens-Above web site.
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