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Astronomy From Your Back Yard - 6/30 to 7/6 2010

By Dave Grosvold

You can spot 1 Ceres any night this week as it moves through the constellation Ophiuchus (pronounced Oh-FEE-eh-kuss) with binoculars or a small scope. Ceres, the largest astronomical body in the asteroid belt, was discovered on Jan 1, 1801 by Giuseppe_Piazzi. After having been designated as a planet in 1801, Ceres enjoyed that elevated status for only a short time, until a number of other small objects were discovered in the space between Jupiter and Mars. In 1802, William Herschel coined the term asteroid ("star-like") to refer to these small bodies — bodies that were too much like stars to be planets, but wandered in the same way.

Ceres was reclassified as a dwarf planet after the status of Pluto was debated and demoted in 2006. Ceres is now the smallest dwarf planet in the Solar System, rather than the largest asteroid, but remains designated formally as 1 Ceres since it was the first such body to be discovered. 1 Ceres is currently still as bright as magnitude 7.3, and can be located by using the finder chart. The best way to distinguish Ceres from the background stars is to observe it on several different nights. The obvious movement from night to night compared to the background will give it away.

Some very bright Iridium Flares may be visible this week! On Wednesday evening, June 30th, Iridium 26 will flare to a magnitude of -3.0 in the WSW at 11:36 PM CDT. Look for it at an altitude of 19° above the horizon. Any time we refer to magnitude in this article, we are actually referring to apparent magnitude, which is how the brightness of an object appears to observers on Earth, as opposed to its intrinsic brightness, or absolute magnitude.

In the early morning hours of Thursday, July 1st, you may be able to catch Iridium 12 flaring to a very bright magnitude -7.0 at 4:16 AM CDT, 27° above the horizon in the ESE. Iridium 23 also flares to a brilliant -7.0 magnitude on Thursday evening at 11:30 PM CDT. Look for it at an altitude of 19° in the WSW. A magnitude of -7.0 is several orders of magnitude brighter than Venus at its brightest! Venus only reaches -4.67 when it is in it s crescent phase and closest to Earth. So these flares will be very bright.

Another pair of bright Iridium Flares appropriately occur on Independence Day, Sunday, July 4th. At 4:04 AM CDT in the ESE, look for Iridium 91 at 23° above the horizon, flaring to a -4.0 magnitude. Again at 11:21 PM in the WSW, Iridium 22 hits magnitude -6.0 at altitude 18°.

Finally, look for Iridium 56 and Iridium 41 in the early morning on Tuesday, July 6th flaring to -5.0 and -7.0 in the SE at 28° and the E at 12° respectively. Iridium 56 will flare at 3:54 AM CDT and Iridium 41 at 5:14 AM, CDT.

The International Space Station (ISS) makes only one pass low in the NNW this week, starting at 11;56 PM CDT on Monday, July 5th. The ISS starts at altitude 10° in the NNW, then barely swings up to a maximum altitude of 11° in the NNW, and quickly fades from view. The ISS will only reach a maximum brightness of magnitude 0.0, or just slightly brighter than Vega in the constellation Lyra at magnitude 0.03.

Venus closes in on Regulus in the constellation Leo day by day, while Mars closes in on Saturn. The diagonal line of Saturn, Mars, Regulus, and Venus is shrinking every day. The three planets will be very close together low in the west at sunset by early August. A telescope shows Saturn's Rings a mere 2° from edge-on right now, but the rings will continue to increase their tilt with respect to Earth over the next 15 years.

The waning gibbous Moon rises around midnight on Friday, July 2nd, and about 45 minutes later, Jupiter rises beneath it. Jupiter is slowly working its way back into the evening sky, and should be a bright Evening Star by mid-autumn, while Venus sinks into the glare of the autumn sunset

As night falls this time of year, look for red Arcturus high in the southwest straight above Spica in the constellation Virgo. The kite shape of the rest of the constellation Bo÷tes extends straight up from Arcturus. By the way, Bo÷tes is pronounced "Bo-OH-teez" or "Bo-OH-tiss," not "BEWT-eez", as some might assume. Pronunciation of constellation names is open to debate, but there are several accepted pronunciations for most constellations. If you're interested, See the Sky & Telescope magazine web site for a Pronunciation Guide.
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