Year’s Wimpiest Full Moon Still Worth Howling At

The nearly full moon and Jupiter shine over downtown Duluth, Minn. US last night. Details: 35mm lens at f/2.8, 1/4″ exposure ISO 800. Credit: Bob King

January’s Full Wolf Moon will blaze over your town from high overhead in the constellation Gemini the Twins tonight. Named for wolf packs that howled outside Indian villages during the cold (and often lean) winter months, the name feels appropriate. Few sounds like a solitary wolf howling on a subzero night give voice to the struggle to stay alive.

Moon on a stick! A beautiful corona formed around last night’s moon when high clouds blew by. Tiny droplets within the clouds diffract the moon’s white light into a bullseye of colored rings. Credit: Bob King

A fist to the moon’s right you’ll see the planet Jupiter, not as close as it was last night but still near enough to catch the eye.

Tonight’s moon is special in a rather odd way. It’s the farthest full moon of the year. Normally I’m writing to alert you about lunar perigee or the closest full moon of the year, better known these days as the “Super Moon”.

Instead, this evening’s moon turns full at 10:52 p.m. CST just 2 hours 59 minutes after reaching apogee or greatest distance from the Earth.

The moon’s distance from Earth varies because it revolves in an elliptical or oval-shaped orbit with the Earth slightly off to one side. Every lunar revolution features a monthly perigee and apogee. When those time coincide with full moon we have either Super Moons or, for lack of a better word, Wimpy Moons.

Perigee and apogee moons from April and October 2007. Credit: Tom Ruen

At apogee at 7:53 p.m. the moon will lie 252,610 miles (406,536 km) from the Earth – about 13,700 miles farther than average and 31,000 miles farther then when closest. That means tonight’s full moon will be about 1/6 or 16% smaller than the biggest Super Moon.

Will you see this with your eyes? Probably not unless you have a photographic memory able to compare the Wolf Moon to the Super Moon of June 23, 2013 six months ago.

The rising or setting moon is one Earth radius (red line) farther from an observer than when it’s high overhead. Illustration: Bob King

Want to see the smallest possible full moon tonight? Catch it at moonrise when it’s farthest from your location. How so?

When rising, the moon is 2% smaller than when overhead because we’re looking across the Earth’s radius (4000 miles) to see it. As the moon rises higher it also gets closer to the Earth, reaching minimum distance when it’s due south. That happens around midnight tonight.

After midnight it spends the rest of the early morning hours moving farther away until it’s again a full Earth radius distance further when perched on the western horizon at sunrise tomorrow. Sounds loony, but it’s true!

6 Responses

    1. astrobob

      It would, but since the illusion applies equally across all full moons. If it were possible to do a direct, side-by-side comparision of moon illusions on June 23, 2013 and tonight, tonight’s moon should appear smaller by some 16%.

    2. Imre

      Because the moon illusion is happening in your head, I think it is not possible to do a measuring comparison. I can remember that my childhood low hanging moons were absolutely gigantic … one could say the moon has moved farther since then.

  1. Sean

    according to Calsky, this full moon was the smallest (obviously appearancewise) as calculated from the geocenter since 817, and until 2154. good luck to any of us trying to stick around for that!

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