tonights_sky

 

"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.  Dave Leake's preview of 2020 sky events can be found here


August 30 – September 5
Wednesday’s full Moon is the Corn Moon or, in China, the Chrysanthemum Moon. This year it’s not the Harvest Moon, however. The Harvest Moon is the full Moon closest to the autumn equinox. In 2020, that occurs in October. Usually one out of every three years, we’ll have the Harvest Moon in October.
On Saturday night, face east after 9:30pm and watch for the rising of the waning gibbous Moon. Only a half degree above the Moon will be the red planet, Mars. Mars continues to brighten as our Earth catches up to it in our faster orbit. Next month it’ll be spectacular! If you want a cool project, chart the position of Mars compared to surrounding stars. More next week! 
 
September 6–12
Have you been watching the planet Mars? If so, you’ll note something odd happening this week (and it will continue through early November). Mars will appear to move backwards! Mars rises due to Earth’s rotation but it’s moving in its orbit west to east. Starting Wednesday, it begins moving east to west. Ancient astronomers had to explain this “retrograde motion” and several odd ideas were developed based on a stationary Earth. But the Earth revolves! And, just like passing a slower car on the highway, as the Earth passes a slower outer planet, it appears to travel backwards. Try charting the motion of Mars maybe twice a week against the distant stars of Pisces. 


September 13–19
Tomorrow morning, early risers will notice the brilliant planet Venus rising in the east after 4 am. A beautiful thin crescent Moon will rise just to the left of Venus. The Moon then slides between the Earth and Sun Thursday and enters the evening sky. When can you first see it? Saturday maybe? Look low in the west.
Jupiter and Saturn are nearly due south after sunset this week as we transition to autumn. Autumn doesn’t have the plethora of bright stars like summer or winter. Our main autumn constellation is the Great Square of Pegasus, the flying horse, though it will look like a diamond about halfway up in the eastern sky. 
 
September 20–26
Use binoculars Monday evening and watch the first quarter Moon pass in front of a double star in the head of Scorpius the Scorpion. Look low in the southwest around 8:45 pm. Such an event is called an “occultation” and was early evidence that the Moon lacked a substantial atmosphere. With a small telescope you may watch one star blink out before the other. A thicker Moon will be below Jupiter Thursday night and below Saturn Friday night. 
The autumn equinox occurs at 8:31 am Tuesday morning signaling the beginning of fall. On this day the Sun is directly above the Earth’s equator and we have roughly the same number of daylight hours as nighttime hours. 
 
September 27 – October 3
Thursday’s full Moon is the fabled “Harvest Moon". The Harvest Moon isn’t any larger or brighter than a typical full Moon but what makes it special is its rise time. As the Moon moves further eastward each night in its orbit, it rises an average of 50 minutes later. But this is an average. The difference in successive rise times is only 25-30 minutes near the first day of autumn. But don’t take my word for it! Note the time the Moon rises this week and compare. Start looking due east as the Sun is setting. And we have a bonus Thursday night as the Moon will be just to the right of the planet Mars.