In Praise Of The Humpbacked Moon

A hump-shaped moon peeks out from a behind a cloud shortly before sunset. Photo: Bob King

We’ve had a lot of clouds around here lately until the last couple nights, when the moon finally broke through the overcast  It cheered me (and maybe the dog, too) to see it shine again on our nightly walks.

Monday’ the Full Hunter’s Moon but for almost a week we’ve been watching the waxing gibbous moon, that curiously-named phase between half (first quarter phase) and full. The name gibbous comes from the Latin ‘gibbus’ meaning humped or hunched. And if you think about it, a gibbous moon does bear a passing resemble to a camel’s hump – circular on one side and slightly flattened but still round on the other.

An 11-day-old waxing gibbous moon. The left side (eastern edge) is called the terminator, the line of advancing sunrise on the moon. At full moon (14 days) sun lights the entire Earth-facing side. Photo: Bob King

Waning gibbous moon begins after full moon and lasts till just before last quarter, when the moon is half again. If you add up all the nights the moon is gibbous it comes to almost two weeks, making it the most commonly visible moon phase.

Two weeks is also about the same number of nights the moon’s a crescent, but crescents set early and rise late. They’re also closer to the sun in the sky and get missed because of glare and low altitude.

The waxing moon is so close to full tonight you’ll need to look closely to see that its outline is not a perfect circle. This map shows the eastern sky below the Great Square of Pegasus around 7:30 p.m. local time. Created with Stellarium

Not so with gibbous. Much more of the moon is illuminated by sunlight and it’s already up in the southeastern sky well before the sun sets. By early evening, a gibbous moon burns brightly against the deepening blue of twilight.

When considering a moonlight ski in mid-winter, we might imagine full moon’s the best time. While it’s true full moon is brightest, it may not always be ideal. You have to wait until later in the evening when the moon’s high enough for its light to penetrate the forest to ski safely. A gibbous moon on the other hand hangs like a lantern high in the south early in the evening. What it might lack in brightness it makes up for in altitude.

The gibbous moons from now through mid-winter will always be high up in the sky during early evening hours for northern hemisphere sky watchers. Consider this an invitation to to bust a hump and experience the joys of gibbousness.

18 Responses

  1. Giorgio Rizzarelli

    Thank you as always Bob for your blog, driven by unconditioned passion for the sky, which I follow daily since months. Even articles like this, about a seemingly known and easy subject, reveal some new information or aspect. I never realized the waxing gibbous phase was the most common, because crescents moons are close to the Sun on ecliptic. And the altitude of the moon in different phases, hours and seasons is a nontrivial subject, I was indeed thinking about it these days.

    1. astrobob

      I am very glad you enjoy the blog and thank you for such kind words. Sometimes I think the obvious – in this case the gibbous moon – gets overlooked. Most everyone knows a crescent, a half and full, but gibbous doesn’t always get the attention it deserves.Thanks again!

      1. Jos. LoGuidice

        Timely topic: While reading and researching American writer H.P. Lovecraft I was made aware of the phrase: gibbous moon.
        Lovecraft, was doesn’t get the attention he deserves, was in the habit of using this phrase to describe evening skies. According to the scholars it is one of his pet phrases.
        It occurs to me that the adjective gibbous could be applied to the Chem-Trails I witnessed above the hills of Duluth this August. The top edge of the Chem-Trail was flat and the bottom of the Chem-trail was scalloped, like a row of double humped camels upside down. The Chem-Trails were
        dripping. Gibbous Chem-Trails in a cross hatch pattern.
        We love your presentations, keep up the good work!
        Jos. 32° 47′ 0″ n

        1. astrobob

          I’m a big Lovecraft fan. I read everything I could get my hands on in high school and early college. I’d forgotten his references to the gibbous moon – thanks!

  2. Jerry Bielicki

    Hi Bob

    I just now say your photos on section B of the April 14, 2012 issue of the Trib.

    My question to you is “How is it that water vapor contrails persist for an hour or two?” Either you’re not aware of the “chemtrail” issue or are lacking some fundamental understanding of our atmosphere and water vapor exhaust from commercial/military jets. Water vapor contrails vanish anywhere between 10 and 20 seconds… the very most.

    Do research and search “chemtrails”. I don’t have an explanation. West coast amateur astromers and sky watchers are more aware of this alleged clandestine NATO project to warm earth’s surface by spraying aluminum and barium dust to reflect the sun and cool regionally parts of the planet. There’s a dvd out there by Michael Murphy explaining in detail this weird man-made phenomena.

    Facts are facts. Water vapor doesn’t hang suspended for an hour or two…..much less get dispresed by winds aloft. Do you have any other explanation? I can’t believe you would intentionally try to misinform your readers, but they should be made aware of the truth.
    See ya! Jerry B.

    1. astrobob

      First, I would never intentionally misinform readers. How does water vapor stay suspended for hours – how about clouds? Clouds stay aloft and build for hours or days. Clouds and contrails are both composed of water vapor. Depending upon factors like upper atmospheric winds, humidity and pressure, they can form and dissolve away in seconds or expand, thicken and linger for hours. This is very basic meteorology. You can check it out in books or online articles on cloud formation.
      I’ve seen contrails disappear in seconds in high, dry air; others expand just like clouds depending on the conditions of the air at that altitude at that time. While there may be talk about how we can use aluminum and barium experimentally, the contrails you and I see every day following high-flying jets are good old water vapor subject to the known laws of physics.

      1. Jerry Bielicki

        Sorry I even worded it that way.
        As of July 2012 for some unknown reason the chemtrails have diminished considerably. They started big time in 2004. At times one could see five to seven of those trails persising over Lake Superior for hours at 40,000 ft. Cirrus clouds, fine and wispy, are the only clouds able to survive at that altitude. First of all you never see that many multi-engine jets flying at one time. Explain that.
        Generally clouds occur in the troposhere. Correct? Chemtrails and contrails are in the stratosphere. Over 8 miles up. Jet water vapor is less dense and never persists at that altitude. I do understand why people resist to believe what sounds like an absurd scenario. I am not the proponent of this clandestine theory. It just exists. There are reports of vegetation failing on the east coast of Hawaii and the California coast…….aluminum and barium poisoning. Again check out the dvd by Murphy. This is not Michael Moore. Michael Murphy. Why is the AAAS taking this serious and doing research; and is fully aware of….in my opinion….a horrific abuse of our atmosphere and every breathing entity on earth? I believe the people of the world deserve an explanation.
        I’ll try to get a copy of that documentary and drop it off at the paper.
        Why can’t the Tribune do a comprehensive report and put all the facts on the table? Still wondering. Clear skies. JB

        1. astrobob

          I’ve seen lots of transcontinental jets flying across the southern sky (over L. Superior). They originate in Chicago, Detroit and other points east and they’re headed west to the West Coast and other destinations. Sometimes I’ve seen them one after another traveling west. It still comes down to the fact we’re dealing with water vapor, whether cirrus clouds or contrails. The height of the troposphere varies depending on latitude but 8 miles is good for mid-northern/southern latitudes. Natural cirrus clouds as well as cirrus clouds spawned by contrails can form there. Here are two links with some good info on contrails: and

          Jerry, there are all kinds of wild ideas out there. One of the most famous was the recent hoo-hah over Comet Elenin and how it was supposedly responsible for causing the big Japanese earthquake a couple years back. There were people out there absolutely sure of this and they’d tote out charts, create videos, use NASA imagery, etc. etc. to “prove” their case. In the end , it was all a lot of junk science and fear-mongering. The comet itself was so small and fragile it broke to pieces and faded away months later. Think of the people that are just as sure we didn’t send 12 men to the moon. Some of that gang sound intelligent and seem to talk science, but they’re utterly wrong. “Chemtrails” and “the military poisoning our atmosphere” involve more junk science and the same sort of misdirected passion that fuels the moon-landing hoax believers. Get the scientific facts on contrails and be skeptical of outrageous claims that the government is deliberately destroying the atmosphere every time you see a long-lasting contrail.
          Just so we’re clear, I’m not saying that seeding experiments to test whether you can stimulate rainfall haven’t been done, just that those are rare instances. What we see day to day is nature at work on common water vapor.

          1. Jerry Bielicki

            Thanks Bob. I totally respect your educated and knowledgeable response to this contrail/chemtrail issue. It’s just that when I saw your photo essay it mentioned nothing about the debate. So when all is said and done I now feel a little embarrased and foolish. I’m not a whacko going off the deep end. I believe Armstrong really walked on the moon and there is no UFO base in Antarctica. Perhaps I did get wrapped up in the fear, but our federal government is not always transparent. I still contend that what I saw in our skies on 9/10/11 was not normal. Seven criss crossing trails all appeared within 20 minutes….and persisted for hours. I’ve got a cell phone photo of the event from Cub Foods parking lot. I’ll get a copy to you. Murphy’s documentary may be on YouTube. I;m questioning everything now. I almost want to say delete all my blogs before they laugh me out of town. Best wishes….Jerry B.

          2. astrobob

            You know I didn’t bring up the debate in that article because I could find no firm evidence, just a lot of youtube videos and frightened talk. There’s no doubt our government isn’t forthcoming about many things, but I remain very skeptical that we’re being inundated with chemicals and viruses (a neighbor of mine believed this) from airplanes. You’re a Sagan fan, so you’ve no doubt heard his famous “extraordinary claims require extraordinary evidence” statement. You should send me the photo you took – I’d like to see it. My address:
            And it would be great if you’d join us at the AAS meeting next month (Nov.14) at 8. Your paintings are holding up well and are still a highlight in the dome!

  3. MBZ

    “. Consider this an invitation to bust a hump and experience the joys of gibbousness.”

    …and the amusements of gullibleousness! 😉
    Great post.

  4. Jerry Bielicki

    I don’t think it’s amusing… I gullible for believing something that nobody has explained. My last post on this………What is the truth?

    1. astrobob

      At least for me, that’s not what I was referring to. MBZ comments regularly and I was making a joke on the word gibbous unrelated to your comment.

      1. Jerry Bielicki

        Misinterpretation miscue. Excuse me.
        Thanks for the kind statement about the paintings.
        I submitted a proposal to Howard to replace the Trifid Nebula with the Hubble image of the illumination nebula in Monoceros. Haven’t heard back from him. Saturn painting needs repair also. I’ll try to be at the next astro meeting. I miss those photos from contributing advanced amateurs. Sagan’s my man. Can you imagine how he would have felt about the Curiosity rover? He bought the ranch way too soon. Cheers.

        1. astrobob

          Didn’t know you were hoping to change and add touch-ups to the paintings. Yes, Sagan would have been the most poetic spokesperson for all these “on the ground” Mars missions if he were still alive.

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