Place Your Bets On Fall’s High-rollin’ Moon

The waning gibbous moon stands out boldly between the evergreens this morning around 9 o’clock. Credit: Bob King

Officially there are four seasons, but we all know that each of those can be subdivided into many mini-seasons. One of my favorites happens in early fall when the last quarter moon stands high in the southwestern sky long after sunrise. I’m not sure what to call this season. Moon In Your Morning Face?

The moon tomorrow morning around 9 a.m. local time high in the west-southwest sky and a tad closer to third or last quarter phase. Stellarium

The waning gibbous moon – the phase between full and last quarter – caught my eye right away when I went to feed the dog this morning. Eggshell white and bright as could be against the blue sky, you couldn’t miss it.

Later, when driving to work, the moon came along for the ride out my window.

It’s the moon’s location along its orbital path that makes it so easy to spot after sunrise in the fall. Both the moon and sun follow the same basic path in the sky called the ecliptic. The sun takes a year to make one complete circuit, the moon only a month.

The sun’s path yearly path across the sky is called the ecliptic. The top of the curve, at right, is the sun’s position during the summer. The low part of the curve is the sun’s location during winter. The up-and-down path is a reflection of the 23 1/2-degree tilt of the Earth’s axis. The tilt makes the sun appear to ride high and then low in the sky over the course of a year. Illustration and animation by Dr. John Lucey, Durham University

During the fall, the sun moves south along the ecliptic, vacating the high perch it occupied during early summer. Since nature abhors an empty stretch of celestial highway, the moon sets up shop in the sun’s summertime digs every autumn for about a week’s worth of time after full moon.

That means the moon’s the high roller now – up all morning just as the sun once commanded the long days of June and July. Have a look for yourself the next clear morning. It’s a wonder really to see the moon hanging there in Earth’s blue sky. Two worlds so close yet so different.

11 Responses

  1. Norman Sanker

    Hey Bob,

    I spent 3 summers in Alaska’s Denali National Park and it seemed plain to me that, if the earth’s axis were perpendicular to its orbital plane, there couldn’t be much–if any–life that far north. It looked like only the intense but short summer season allowed enough vegetative growth to support the arctic web of life. (A saying in Alaska: “June is spring, July is summer, August is autumn–the rest is winter.”) My question: Is there some optimal axial tilt to maximize plant growth over the course of a year in the subarctic and subantarctic regions? The math is over my head and I’m not religious so divine intervention is out, but this 23 degree tilt seems to work well. On a different subject: with all this speculation about ISON, I have one simple question. Has any comet ever passed this close to the sun (about one solar radius), survived the trip, and failed to put on a good show after perihelion? That seems highly improbable to me. Keep up the good work.

    Norman Sanker

    1. astrobob

      Great questions! About the axis, I don’t feel qualified to give a definitive answer, but would guess that if Earth’s axis were perpendicular (0 degrees tilt) Alaska might fair far better than it does now. The sun would always lie on the celestial equator, which from Anchorage is 29 degrees above the horizon at noon. So the sun would be stuck forever traveling the same arc in the sky it currently does on the first day of fall and spring. There would be no winter. Maybe somewhere in between would be ideal, say a 12 degree tip. Of course, life is in synch with its environment, so any radical shift in tilt would radically alter the balance of species.
      Plenty of comets have passed one solar radius or closer to the sun and broken up, but if a comet survives it should put on a great post-perihelion show provided it’s heading in a direction that takes it away from the sun into a dark sky. Once again, I don’t think I can answer your question without doing a fair amount of research. It’s easy to find comets that survived and looked great. Not so easy to go through all the data to find the duds.

  2. Edward M. Boll

    The Moon is too bright and Encke too faint. But I was going to make my first attempt of the comet at 1:30 A.M. with large binoculars. I stepped outside and it looked so calm and clear. But after working 2 jobs and 60 hours this past week, I yielded to the flesh and went back to bed.

    1. astrobob

      I know the feeling. I’ve been wanting to get up 6 to look at Mars but it’s really hard after I’ve been out till 11 looking at comets, etc. with the scope. How large are your binoculars? Good luck with Encke – it’s still pretty faint but hopefully not for long.

  3. Edward M. Boll

    20 by 60’s. I have been pretty satisfied with their performance. I have seen a lot more comets with them than I did with the 10 by 50’s, I had bought before.

    1. astrobob

      60mm gives great reach. I mostly use 8x40s but my wide-angle 10x50s give a beautiful view of the Milky Way. With them I can see stars down to around mag. 9.5.

  4. Robert

    Hi Bob- I have noticed even as a kid that the full moon in the summer tends to mimic the winter sun and really noticeable I think is the winter full moon which is usually almost directly overhead and would mimic the summer sun thus we get the moon on the breast of the new fallen snow gives a luster of mid day to objects below, if the full moon wasn’t high in the sky in winter we would get ” gave a luster of afternoon or morning to objects below” and that would just be wrong. Just a thought.

    1. astrobob

      You’re so right about that. I also think about the shadows and lighting of summer when I see the winter full moon lighting the snow.

  5. caralex

    We’ve had bright, sunny, cloudless skies here for the past two days, and as you say, Bob, the moon in the morning is riding high and bright. I always love it when it catches me by surprise when I’m not expecting it!

      1. caralex

        Yes, and I once read a comment on a YouTube video of an apparent anomaly, breathlessly asking ‘What’s that? It can’t be the moon because it’s day time’.

        You can’t fix stupid, it seems!

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