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Night Sky

Night Sky on July 15 at 9:30 p.m.

July 2010

—Charlie Christmann

New Comet Going and Gone

Did anyone catch Comet McNaught (C/2009 R1) early mornings before sunrise the first half of June? The comet will reach its closest approach to the sun on July 2nd. Reports indicate that this is most likely a brand new comet, making its first trip around the sun.

By mid June, the comet was visible as a fuzzy spot in the east, away from the city lights, and brightened to a 4th magnitude by June 20th as it approached the sun on its hyperbolic trajectory. After the 2nd, the comet will be visible in the southern sky after sunset as it recedes; unfortunately, those in the southern hemisphere will have a much better view. A few days before and after July 2nd, the comet should be a naked eye object just before the dawn sky or just after dusk. Binoculars will definitely help with the experience.

When viewing the comet with a telescope or binoculars, look for the greenish head and the bluish long tail. The green is produced by cyanogen (CN) and diatomic carbon (C2) in a comet’s coma fluorescing green in sunlight. Ionized carbon monoxide (CO+) and carbon dioxide (CO2+) in the ion tail fluoresce blue. What little dust is flowing off into a tail dust simply reflects sunlight, looking a yellow-orange color. McNaught is not a very dusty comet.

Want a great daytime view of the comet? All you need do is head south on July 11th for the full eclipse of the sun in Mangaia (Cook Islands) and Easter Island (Isla de Pascua) in the South Pacific, or try southern Chile and Argentina in South America. During the eclipse, the C/2009 R1 comet will be an interesting sight.

 In the not too distant past, comets were seen as omens of evil, a sign of something bad about to happen, such as plagues or war. Today, we know comets are icy bodies expelled from the far outer reaches of the solar system. This region is called the Kuiper Belt. Pluto (the former planet) is thought to reside in the inner reaches of the Kuiper Belt.

Occasionally, the orbit of a Kuiper Belt object will be disturbed by Neptune or perhaps by an unseen object passing near our solar system. In some cases, the disturbed object will fall toward the sun to become a comet. Objects even further out can also become comets. The Oort cloud is a shell surrounding our solar system and has an untold number of potential comets.

Depending upon its orbit, a comet can be periodic, like Haley’s comet that visits every 76 years. Others meet their final fate, crashing into the sun or a planet, like Comet P/Shoemaker-Levy 9 did at Jupiter. Comets on a hyperbolic course, like this McNaught comet, will never return as they fly once past the sun and then out into the cold cosmos.

C/2009 R1 is just one of more than 50 comets found by astronomer Robert H. McNaught from Australia’s Siding Spring Observatory. They all bear his name.

The Planets and Moon

Mercury will be in the western sky about 30 minutes after sunset the last two weeks of July.

Venus will still be bright, just a bit north of west after sunset. About 40 minutes after sunset in the west, you will find the crescent waxing Moon seven degrees to the lower left of Venus. Regulus, Leo’s brightest star, is five degrees to the lower right of Venus.

Earth reaches aphelion (farthest distance from the sun in its elliptical orbit) on the 6th at 8:00 a.m. MDT. At this time, the Earth is moving slower than at its closest point. Because of this, the northern summer is the longest season of the year.

Mars will be just south of west and a bit higher than Venus after sunset. There is a Mars-Saturn conjunction scheduled for the 30th. Use binoculars about an hour after sunset. The planets will be near the western horizon, to the upper right of Venus.

Jupiter is rising in the east around midnight this month. On the 3rd, look about 90 minutes before sunrise for a Moon-Jupiter conjunction in the constellation Pisces.

Saturn can be found just south of Mars in the west after sunset. A three-way conjunction of the Moon, Mars, and Saturn occurs an hour after sunset on the 15th. Regulus will be to the lower right of Venus. Looking along a line from Regulus to Venus, you will find Mars, Saturn, and Spica. The Moon will be below Mars.

The Moon is new at 1:40 p.m. MDT on the 11th and full at 7:36 p.m. MDT on the 25th.

On the 4th, I predict many exploding stars above the cities and towns across the good ‘ol USofA.






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