The Wheel Of The Sky Goes Round And Round

One regular-sized flake and one tiny one dress up my deck this morning after a light snowfall last night. Photo: Bob King

I know, I know. I should have taken a picture instead of describing to you know how incredible it was to see hundreds of snowflakes silhouetted against the gibbous moon last night. When I went to walk the dog, I was struck by the unusual combination of snow and moonlight. The clouds were thin enough to reveal individual flakes flying past the moon like runners in front of a spotlight. The best I could do was photograph the the pillowy piles of snowflakes on my deck this morning. A flake is composed of ordinary water molecules but who isn’t amazed by how much beauty is wrought by so minute and simple an ingredient?

Not only will the moon and Mars be close tonight (Thurs.) but there are other bright stars in their vicinity to spark up the scene. This may shows the sky around 7 o’clock. Created with Stellarium

Tonight the moon will return but according to our local forecast without snowy accompaniment. Not that the moon will be lonesome. Far from it. It’s in conjunction with the brilliant planet Mars, and the two will certainly catch your attention if you’re out and about. Look high in the eastern sky. Mars will sit atop the waxing gibbous moon.

Yesterday one of our readers, Andrew Kirk, wondered if there was a time-exposure photo available of the Magellanic Clouds circling around Sigma Octantis, the southern pole star. After some digging and contacting, I’m pleased to share with you several very nice images of star trail photos of both northern and southern skies. Enjoy!

This award-winning photo was taken by Australian Ted Dobosz while camping in the Blue Mountains near Sydney. It’s a half-hour long time exposure aimed at the south celestial pole and shows the Large and Small Magellanic Clouds (right of center). The stars and Clouds trailed during the exposure because of Earth’s rotation. No trailing is seen at the pole because it lies in the direction of our planet’s south polar axis. The orange glow is light pollution. For the full-sized version, please click HERE. Details: 17mm lens at f/4.5, 30-minute exposure at ISO 400. Credit and copyright: Ted Dobosz

Another amazing view of the southern sky and dim southern pole star Sigma Octantis from the shore of Lake Titicaca in Bolivia. The bright band at upper right is the Milky Way. This very long exposure shows well the apparent motion of the stars due to Earth’s rotation. Details: 16mm lens at f/4, 2-hour exposure at ISO 800. See more nice star trail photos HERE. Credit and copyright: Fred Espenek

Let’s return now to the northern hemisphere and take a look at how stars circle about Polaris. While you may have had a hard time finding the southern pole star in the photos above, you can’t miss the tiny, bright arc of the North Star near the center of this picture. For more photos by the photographer, please click HERE. Credit and copyright: Kirk Rogers

This time exposure was taken in the forest north of Duluth a few years back. Can you find the outline of the Big Dipper in the seven bright trails at top? Photo: Bob King

If you’d like to make your own star trail photos of the stars near the north or south celestial pole, you’ll need a camera that can take a long time exposure and a tripod to put it on. Go out to a dark sky site on a moonless night and use a wide angle lens — something in the range of 24mm or wider. Frame your picture with an interesting foreground, set your f-stop on the lens to f/4 or 4.5, and lock your camera shutter open with a cable release. Try an exposure of at least 15 minutes. If your sky is really dark, you can go for an hour or longer. You’ll love the results.

8 Responses

  1. SteinInez27

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  2. granfred

    Well, I would say, that such a picture as that taken from lake Titicaca should be impossible, as the Earth is spining and wobling.
    This result is only possible if the photograph is just on the axis, and aiming at one of the Polar stars, and this supose the axis stay always aligned with the star.
    So either this, is a fake
    or the Earth is not spining, whereas, the sky is.
    And so, if the Earth is not spining, the sun revolves around the Earth, but, as there are seasons, this means the Earth has to be flat.

    So are you kidding us ?

    1. astrobob

      Whoa! The Earth is spinning alright. Its south polar axis points to a spot in the southern sky near the dim star Sigma Octantis. The much brighter Polaris (North Star) happens to be where the NORTH polar axis points. The thing to remember is that Earth’s axis points north AND south, so people in both hemispheres see star trails. The wobble, called precession, isn’t an overnight thing, but requires 26,000 years to see a full cycle. It’s a VERY SLOW process and not visible to the eye even over a lifetime.

      1. caralex

        Bob, can the tiny circle Polaris makes each night be seen with the naked eye at all? How wide is it (in degrees)?

        1. astrobob

          Hi Carol,
          Yes, but you’ll need a marker as it’s just 3/4 degree from the pole. It therefore describes a circle 1.5 degrees in diameter. It would be a fun experiment on a long winter night to carefully align it with a distant landmark at dusk and then again at dawn when it was on the opposite side of its 1.5 degree circle.

          1. caralex

            Thanks, Bob. Thought so. Still 1.5 degrees is a fair size circle, isn’t it? It’s about 3 moon diameters, so theoretically, it should be possible to see its motion, if you lined it up, as you say.

          2. astrobob

            I’ve never deliberately looked so I’ve never seen it move. Shows up very well in photos, even those taken with a wide-angle lens.

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