Moon At Last Quarter, Aurora On Deck

The top branches of a poplar tree frame the last quarter moon this morning (Oct. 22). Last quarter or third quarter refers to the moon
Branches of a poplar tree frame the last quarter moon this morning (Oct. 22). First quarter phase, often called the ‘the half moon’, refers to the moon completing a quarter of its orbit around the Earth. The last quarter moon has completed three-quarters of its orbit around the planet. Credit: Bob King 

Beautiful blue sky morning. I walked the dog, noted the light coating of frost on the lawn and looked up to see a crisp last quarter moon riding over the poplar tops. Only a few yellow-brown leaves wagged way up there, but the contrasts of sky, moon and autumnal color made for a refreshing way to start the day.

After full moon, we often lose track of the moon’s doing because it rises later and later at night. Up until full moon, it’s always up in the afternoon or early evening sky, making it hard to miss. Each day (or night), the moon moves about a fist to the east or left as seen in the northern hemisphere. The full moon rises at sunset, the day after full about an hour later, and the day after that another hour later. By the time of last quarter phase or seven days past full, the moon rises around midnight, a time when many of us are in bed.

The curved lines represent magnetic field lines looping out and back from the sun in this photo taken in ultraviolet light by NASA's Solar Dynamics Explorer. Field lines - which carry electrons and protons from the sun's atmosphere - are free to leave he sun (arrows) in a coronal hole and stream into space.
The curved lines represent magnetic field lines looping out and back from the sun in this photo taken in ultraviolet light by NASA’s Solar Dynamics Explorer. The field is wide open in a coronal hole (bottom), allowing solar particles to travel freely into space and affect the Earth and other planets. Credit: NASA

By sunrise, the last quarter stands straight up due south at its maximum altitude. And since the sun rises so late in late October (after 7:30 a.m. from many locations), it’s easy to spot the last quarter moon high in the southwestern sky anytime from sunrise till 11 in the morning.

Late-rising moons are great times for aurora watching because the sky remains dark for much of the night. This weekend, space weather experts predict minor G1 geomagnetic storms. We might see a low arc or two in the northern sky early this evening (Oct. 22) with better chances for a more extended and active aurora Sunday night Oct. 23. Solar coronal holes and a glancing blow from a CME or coronal mass ejection are treat-or-treating our planet with a bounty of electrons and protons.

2 Responses

  1. caralex

    You’d be amazed at the number of people who, on noticing the moon in the daytime sky for the first time, freak out, thinking there’s something wrong in the heavens! They don’t seem to grasp the concept that the moon revolves around the earth and spends as much time in the daytime sky as it does in the night sky!

    1. astrobob

      Carol,
      I know! Many are surprised to see it in the daytime, the reason I’ll occasionally write about it in the blog.

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