As we pass though the September Equinox, nights grow longer in the northern hemisphere and shorter south of the equator. Objects northerners look forward to in fall and winter are spring and summer gems down under. Whatever your season, there are plenty of telescopic and binocular points of interest this month.
Jupiter Opposition
The king of the planets takes center stage in September, reaching opposition on the 26th of the month. The Earth will sit precisely between the Sun and Jupiter, with Jupiter rising at sunset and setting at sunrise. At a distance of 3.95 A.U. and shining at magnitude -2.9, it is a whopping 48.8 arc-seconds in apparent size. The Great Red Spot, loads of inky black shadow transits, festoons and white ovals marching along the equatorial belts. Watch for nights of steady atmospheric seeing (no jet stream overhead) to maximize this event!
New Moon
This month's new Moon is September 25th at 14:54 PDT. With northern nights growing longer and now exceeding daylight hours, take advantage of deep sky targets when the Moon is absent and weather still cooperates. Southerners, you have the opposite, with shortening nights but improving weather.
The first week of the month features lunar observing, with the Moon and Jupiter making a nice pair on the 10th and 11th. The summer Milky Way is still up but has already transited the meridian, so grab views of your favorite open clusters and planetary nebulae as they head toward the western horizon increasingly each night. Watch for favorites such as the Helix Nebula, the condensed globular cluster M15 and the Andromeda Galaxy taking center stage.
Andromeda And Triangulum Galaxies
The two targets this month are the Andromeda and Triangulum galaxies, known as Messier 31 and Messier 33 respectively, and they are in prime view all month long. Both are members of our Local Group of galaxies, which in total cover over 10 million light years. The largest of the Local Group is the M31, with our home Milky Way Galaxy the next largest. Find the Local Group Of Galaxies Wikipedia page for a stunning list of our galactic family. Both M31 and M33 are visible in binoculars, with the latter the bigger challenge in even dark skies. M31 is huge, covering an area of five full Moons along its longest axis. A telescope view shows an intense core, spiral arms with dark lanes, a blue supergiant star cluster's glow, and two satellite galaxies (M32 and M110). M33 is a face on spiral galaxy, dim but viewed with certainty, containing spiral arms, a brighter core and glowing HII regions where nebulae are creating new stars. These are the top highlights, but there are near endless fascinating objects awaiting your exploration.
September Challenge Object
Astronomer George Abell is known for his catalogues of galaxy clusters and planetary nebulae, with Abell 70 ranking among the more visually interesting of the planetaries. In Aquila, a constellation called by some the graveyard of stars for its numerous planetary nebulae (dying stars), Abell 70 sits 13,500 to 17,500 light years distant, covering an area of sky covering 40x30 arc-seconds, and is annular, and clearly showing its edges as a ring shape with a darkened interior. At magnitude 14-14.3, it is visible with averted vision, but using an Oxygen III filter brings it into clear direct view. Why is this seen as a diamond ring? A chance alignment of a galaxy at 253 million light years shines through the north edge of the planetary, setting a 15x8 arc-second "stone" on the ring. Also of interest is the planetary nebula's central "star" — a binary consisting of a white dwarf and barium star!
All objects described above can easily be seen with the suggested equipment from a dark sky site, a viewing location some distance away from city lights where light pollution and when bright moonlight does not overpower the stars.
