This month is an excellent time to explore the outer reaches of our solar system, as all of the giant planets are well placed for observing.
Jupiter and Saturn remain prominent all night and are certainly the stars of this planetary parade, but their less observed, more distant siblings, are also observable. Uranus and Neptune are rightly called “ice giants,” a nod to their fundamental differences from the “gas giants,” Jupiter and Saturn. The gas giants are composed mostly of hydrogen and helium. Our ice giants are made of heavier elements: oxygen, nitrogen, carbon, and sulfur – the next most abundant elements in the Sun after hydrogen and helium. Being less massive, they were unable to hold onto the lightest elements as the planets were forming. Residing so far from the sun, they are composed mostly of ices.
Neptune is at opposition around September 10. It is at its brightest and largest angular size for the year. That’s still a dim 7.8 magnitude and a tiny 2.3 arc second disk, but hey, it’s close to three billion miles from us. It should be visible in a pair of binoculars and is easily found due to its proximity to a naked eye star, “phi Aquarii,” on the eastern edge of the constellation. Look for the Greek letter ϕ on your star chart. Neptune is so far away from us that it appears to move quite slowly. It takes all month for it to move the apparent diameter of the moon, so it will be in the same binocular field with that star all month. It will look like a star in your binoculars; it takes a telescope to see it as a tiny disk.
Uranus is headed for its October opposition, but it is now rising before midnight. It is found in the constellation of Aries and is obvious in binoculars. In fact, sharp-eyed observers with dark skies should be able to see it with the unaided eye once you know where to look. The fact that this (admittedly marginally) naked eye planet avoided detection until the advent of the telescope attests to its slow movement through our sky. It takes 84 years to make one trip around the sun. It’s twice the angular size of more distant Neptune, but still rather small at 3.6 arc seconds in diameter.
September’s sky is filled with so much more than the planets of course. The universe beyond the reaches of our solar neighborhood is filled with celestial wonders that can be enjoyed with telescopes of any size, binoculars, and even the unaided eye. To fully appreciate it, though, it helps to know just what is out there. A resource that you’ll find helpful is the free monthly star map available at http://www.skymaps.com/ . The map will show you the current sky for the month. It has a sky calendar with all of the month’s celestial events and lists of observable objects for naked eye, binoculars or the telescope.
Another excellent resource are the videos from the Space Science Telescope Institute called “Tonight’s Sky” and NASA’s JPL offering “What’s Up”. Both links can be found on the website of the Huachuca Astronomy Club www.hacastronomy.org . The videos will give you a tour of the night sky customized for the calendar month.
Of course, there is no better source of sky information and inspiration than your local astronomy club. Members of the Huachuca Astronomy Club are always willing to share their knowledge, their enthusiasm, and their telescopes to help you enjoy the night sky. You can meet club members at their monthly meetings held at Cochise College and hear exciting talks by professional and advanced amateur astronomers. The next meeting is on Friday, September 13 at 7 pm. It is open to the public and admission is free. Membership in the astronomy club is open to anyone – and it’s easy, just click on the “Join” link at www.hacastronomy.org.
Another way to connect with the club is by attending the free monthly open house observing session at the Patterson Observatory on the campus of the University of Arizona, Sierra Vista. Volunteers from the astronomy club run the observatory for the University South Foundation, which makes the observatory available free of charge. The September session at Patterson will be held on the 5th, weather permitting. Doors open at 7 p.m. If you like to observe the night sky, you’ll enjoy this free, family-friendly event.
Don’t forget to mark your calendars for the annual Dine Under the Stars scholarship fundraiser on Oct. 5. The Patterson Observatory will be open for stargazing during the event hosted by the University South Foundation. This year’s theme is “Mardi Gras” and should be a lot of fun, raising money for a great cause. Visit www.universitysouthfoundation.com for more information.