Driftless Dark Skies: Lunar Time

When I was a high school teacher, we sometimes had the ritual of starting class with a student letting us know the phase of the moon and when it would rise and set. We spent too much of the day cut off from fresh air and sunlight, and it seemed that such a custom might help teens be more in sync with natural cycles. I invite you to experience the rhythm of the moon this month.

The moon is at first quarter on April 30.  The side of the moon facing us is half in sunlight and half in darkness. The line dividing the two halves is called the terminator, and it’s where the sun is rising on the moon. If you have binoculars, scan along that line where the shadows at lunar dawn make it easy to see the mountain and plains and craters. At first quarter, the moon rises around noon and sets around midnight. Watch the first week of May as it waxes to a gibbous phase and rises and sets about an hour later every day.

Full moon is on May 7. Now the near side of the moon is totally in sunlight. It rises when the sun sets and sets when the sun rises. There is no terminator to exaggerate its features, but you can easily see the lighter colored highlands, the darker colored lava seas, and even rays of ejecta coming out from some of the larger craters.

The moon wanes to gibbous the second week of May until it reaches last quarter on May 14. Now the terminator marks where the sun is setting on the moon. It rises after midnight and can even be seen in the daytime before it sets after noon. I like the ritual of heading out in the morning before sunrise to check in on the stars and planets. On May 12, look for Jupiter above the moon. On May 13, Saturn is to the right of the moon. On May 14, Mars is to the left of the moon and on its right on May 15.

The new moon is on May 22, but we never see that (except during a solar eclipse) because the moon and sun rise and set together and the nearside of the moon is in darkness. But start watching for the waxing crescent moon in the western sky after sunset the last week of May. Look for Venus above the moon on May 23 and below it on May 24. Venus was spectacular all winter and spring. This is our last chance to see the “evening star” in 2020 before it becomes the “morning star” this summer and fall. With binoculars, it may be possible to see that Venus has a crescent shape much like the moon. While you have your binoculars out, scan for Mercury above and left of Venus as you end your day under the starry skies. First quarter is on May 29, and you have experienced a full lunar cycle!

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador and with the IAU as a Dark Skies Ambassador. 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.