"Tonight's Sky" is written by retired planetarium director Dave Leake and reprinted with his permission. See Dave Leake's Prairie Skies column in the Champaign–Urbana News-Gazette each Sunday.

August 28 – September 3

Mars rises in east-northeast at about midnight all this week. It will appear like a reddish star shining with a steady light. Tomorrow Mars sits between the Pleiades star cluster and the V-shaped Hyades cluster marking the face of Taurus, the Bull. Keep watching as Mars will move into the Hyades this weekend, appearing as the Bull’s other eye, along with the red star Aldebaran.

You’ll find a first quarter Moon in the evening sky this Saturday which means time for another CU Astronomical Society open house at their observatory southwest of town. If the weather permits, we’ll start around sunset and it’s free. See for details and call 217/351-2567 if you’re unsure of the weather.

September 4–10

Venus is getting closer to the Sun in our morning sky, so you have to catch it low in the east right before the dawn. If you look tomorrow morning, Venus appears less than a degree from the star Regulus, the heart of our lion. On Thursday evening Mars is near the eye of our bull, Aldebaran, rising in the east-northeast at midnight. It will look like the bull has two red eyes! The Harvest Moon brightens our Saturday evening. Jupiter will be to the left of the Moon that evening. The Harvest Moon is the full Moon that occurs nearest the autumn equinox. It’s not brighter or larger than a regular Moon but the Moon rises at nearly the same time each evening. 

September 11–17

The Moon travels further eastward each evening and we see less of the illuminated side. By Friday, a waning gibbous Moon rises near midnight and makes a nice triangle with Mars and the red star Aldebaran, with Mars to the lower left of the Moon. Saturday’s third quarter Moon is in line with the planet and the star. Friday is also Neptune’s opposition date, a time when it’s closest to our Earth. You’ll have to use a telescope and know just where to look in Aquarius to find it. Next week we celebrate the 176th anniversary of Neptune’s discovery. Given it takes 164 years to orbit the Sun once, Neptune just completed one revolution since its discovery just over a decade ago! 

September 18–24

The autumnal equinox is upon us this Thursday! This is a time when the Sun appears directly above the Earth’s equator at noon. For us, the Sun appears about 50 degrees high at mid-day. In fact, the Sun would always appear this high at noon from our latitude, but the Earth’s rotational axis has a 23.5 degree tilt to it. Because of that the Sun is 23.5 degrees higher in the summers (73.5 degrees) and 23.5 degrees lower in winter (26.5 degrees). Of course, “equinox” means “equal night” when we expect to have the same number of daylight as nighttime hours. Due to the Earth’s atmosphere refracting sunlight, we actually have close to exactly a 12-hour day on the 26th

September 25 – October 1

The “king” of our solar system, Jupiter, reaches opposition Monday evening. If you’re a regular reader, you know Jupiter is opposite the Sun from our point of view, rising at sunset, and is both close to us and thus large through a telescope. You can get a great view of Jupiter several weeks on either side of this date. Look for it rising nearly due east as the sky darkens. You can’t miss it as it will be the brightest star-like object there. As it gets higher in the sky, note how it doesn’t twinkle like the other stars do. If the skies are clear, get a good look at Jupiter at our next CU Astronomical Society open house Saturday night at dusk.