September is here, when summer comes to an end and fall begins. The Autumnal Equinox occurs this year on Sept. 23, when the Sun crosses the equator, going south. Night and day are of approximately equal length at that time.
Jupiter and Saturn, the solar system’s largest planets, still dominate the southern evening sky, even though they are now farther away from us than last month. Jupiter is now in the southwest and sets in the late evening hours. It is still large enough to be impressive in a telescope, and the four large Galilean moons are visible. Saturn remains higher in the southern sky in September, setting after midnight, and is still impressive in a telescope.
The inner planets – Mercury, Venus, and Mars, are all missing from the evening sky, but the outer planets Uranus and Neptune join Jupiter and Saturn during September nights. Uranus is technically visible to the naked eye but is too dim to easily pick out from nearby stars. Neptune is not visible to the naked eye and requires a telescope to see. Neptune reaches opposition, when it is closest to us, on Sept. 8.
Those four outer planets – Jupiter, Saturn, Uranus, and Neptune – give you a feeling for how large the solar system is. In September, Jupiter will be about 500 million miles from us. Saturn will be almost twice that far, about 900 million miles. But they are neighbors compared to Uranus (about 1,700,000 miles distant) and Neptune (2,680,000 miles).
To put those distances in perspective, let’s say we traveled to them in a spacecraft that went at the speed of the fastest Apollo Moon mission – over 24,000 miles per hour. Even at that speed, a trip to Jupiter would take over 2 years, Saturn 4 years, Uranus almost 8, and Neptune over 12 years. The solar system is big!
September will be a good month for viewing the International Space Station. Some good evening passes will be on Sept. 21 at about 8:45 p.m., and Sept. 22 at about 7:55 p.m. If you are an early riser, check out Sept. 11 at about 5:45 a.m. Until mid-September, the ISS will only be visible in the morning. As time gets closer, use the website Heavens-Above (heavens-above.com) to get a more accurate time for the flyover.
Fall constellations, such as Pegasus and Andromeda, are rising in the east during September. Look for the “great square” of Pegasus low in the east after sunset. The square, made up of 4 almost identically bright stars, is “tilted” as you view it, and it might look to you more like a baseball diamond.
Andromeda lies to the left of Pegasus, and includes the Andromeda galaxy, another galaxy that is visible to the naked eye. The galaxy is quite faint and requires a dark sky to see it. Get the location from the picture with this column and use a pair of binoculars to help locate it. You’ll see an oval smudge of light, that’s it. You are looking at light that left the galaxy about 2.5 million years ago.
Enjoy September’s skies!