Driftless Dark Skies

John Heasley

October begins and ends with a full moon. On Oct. 1, the Full Harvest Moon rises in the east around 7:05 p.m. right after the sun sets in the west at 6:45. The Harvest Moon is the one closest to the Autumnal Equinox on Sept. 22. And because lunar cycles are 29.5 days long, October ends with a second full moon on Oct. 31 rising in the east at 6:15 p.m. right after the sun sets at 5:55. This one is often called the Hunter’s Moon, but Halloween Moon seems very appropriate for this year.

Mars is the brightest planet in the evening sky this month. Watch for it rising in the east after sunset and shining all night long as it passes high through the southern skies before setting in the west around sunrise. It’s farther from the sun and orbits it more slowly with a year almost twice as long as ours. Every 25-27 months, our planet “laps” the red planet and we pass between the sun and Mars. Earth and Mars are especially close this year.  On Oct. 6, we are separated by only 36 million miles. Still, it takes the sunlight we see reflected by Mars 200 seconds to reach us. We won’t be this close again until September 2035. Because our orbits are not perfectly round, it’s another week before Earth passes between the sun and Mars. On Oct. 13, be sure to observe Martian Syzygy Day when sun, Earth and Mars are all in a line.

Mars has long lured the attention of skygazers because of the way it appears to wander through the fixed stars, sometimes even appearing to reverse direction as it makes its way through the constellations of the zodiac. And humans have been awed by the way its brightness increases a hundredfold as it flares forth every two years. Much less mystifying once we figured out that both are worlds orbiting the same star.

October is also a wonderful month to enjoy the moon and Mars together. They will be just a finger’s width apart as they travel across the sky on Oct. 2. The moon’s orbit brings it past Mars again later in the month. On Oct. 28, the waxing gibbous moon will be to the right of Mars and then to its left the next evening on Oct. 29. These are good nights to consider the size of things. Mars is about twice the diameter of the moon, but appears 80 times smaller because it is 150 times more distant from us. If you have binoculars bring them out to tour the landscape of the moon, but also to enjoy even more the magnificent color of Mars.

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. For more information about stargazing in southwestern Wisconsin, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies above.