Looking west from Astroguyz HQ Oct 27th at sunset. (Created by the Author using Starry Night & Paint).
This week marks the return of the King of the Planets to evening skies, as well as a close lunar-planetary grouping for well placed observers and a chance to spy an unusual asteroid.
1st up, the planet Jupiter reaches opposition on the night of the 28-29th, shining at magnitude -2.9 on the Pisces-Aries border. Rising in the east just as the Sun sets, this opposition is not quite as close as last yearís at 369 million miles distant, or only 0.4% farther. Fans will remember that the 2010 opposition was the closest since 1963. Note with an apparent disk of 50Ē arc seconds in size, the planet Jupiter only currently sits a few degrees below the ecliptic, and thus the planet and its moons cast shadows almost directly behind from our point of viewÖ that will change dramatically as Jupiter heads towards quadrature in January 18th, 2012. Jupiter passed perihelion on March 17th of this year.
Next up is an interesting tri-conjunction involving the planets Mercury, Venus and a very slim crescent Moon low in the dusk skies on the 27th, with an occultation of Mercury by the Moon for those lucky Australian and New Zealand-based observers on the 28th. (Hey, who says we never write about southern hemisphere events?) The Moon will reach New phase on October 26th, at 19:56UT, and there is a chance for observers in South America and the southern United States to catch Venus, Mercury and a 26-30 hour old Moon low in the weeds on the 27th immediately after sunset. This is a challenging photo op; Venus (magnitude -3.9) will be the easiest target to acquire, allowing you to hop via binoculars or a telescope down to fainter Mercury (magnitude -0.3) and finally acquire the razor thin Moon. For those going after the Mercury occultation, the event is centered around 02:00 UT on the 28th.
But thereís moreÖ while in the vicinity of Jupiter, try your skills at tracking down asteroid 1036 Ganymed. No, thatís not a typo. Ganymed was first discovered by astronomer Walter Baade in 1924 and shares the namesake of Jupiterís largest moon, Ganymede, forsaking the extra Ďeí. (IAU rules state that two solar system objects cannot have the same name). With a† 4.34 year orbital period, this Mars crosser (see below) was only 0.36 AU from Earth on Oct-13th, the closest itís been since its discovery, and wonít pass us as close until Oct 12th, 2137 at nearly the same distance. Interestingly, 1036 Ganymed will pass Mars at 0.09 AU in 2050 and again at 0.03 AU in 2176. The asteroid reached perihelion on September 1st and opposition occurs on October 29th about two degrees from the planet Jupiter. Ganymed will be gliding through the constellation Aries, and passes within one degree of the bright star Hamal on the night of the 21st. Shining at magnitude +8.3. Now is a chance to see the brightest of this unusual class of asteroid!
The Astronomy Term of the Week is Amor asteroid. This is a class of asteroids that approach but do not cross the orbit of the planet Earth, and for the most part cross the orbit of the planet Mars. Aforementioned 1036 Ganymed is the largest member (at 32 km) discovered. The class itself is named after asteroid 1221 Amor discovered in 1932. Another famous Amor member includes 433 Eros, which was visited by the NEAR Shoemaker spacecraft in 2000. Interestingly, Marsís moons Deimos and Phobos are thought to be captured Amor asteroids as well; Russiaís Phobos-Grunt spacecraft is set to launch next month and may perform the first successful landing (or would you say docking?) on a Martian moon. 1036 Ganymed has some close encounters (see above) with the Red Planet, and may become yet another Martian moon/impactor in the far distant future.