The skies reflect our spinning world

By Phil Plait | October 11, 2011 9:57 am

We live on a spinning ball, rotating madly as it moves through space. Once every day the surface of our planet makes a circuit around the imaginary line connecting its poles… well, imaginary it may be, but the effects are quite real, especially when you take long exposures of the night sky. That’s what photographer Brad Goldpaint did, and created this lovely time lapse video he calls Breaking Point:

[If you go to the Vimeo page for the video you can watch it in HD, which you really need to do, as well as make it full screen.]

Amazing, isn’t it? The visual of the stars wheeling around the sky over our head invokes such a wonderful feeling, as if the whole Universe is spinning around us. But it can also be a little odd-looking too. For example, take a look at this picture Brad composed using some of the images he crafted into the video, which he has singled out and called Delineated:

[Click to siderealate.]

Strange, isn’t it? For one thing, it isn’t one long exposure, but instead composed of 60 short exposures added together. If you squint you might see streaks of light, but in reality those arcs are composed of individual dots, the images of stars frozen as they moved across the sky.

It’s also a bit odd due to the fuzzy glow at the bottom. That’s actually the smeared-out light from the Milky Way galaxy as it rose into the frame. Not being a point-like source of light like stars, it has a dreamier, fuzzier quality. Again, from the video, here’s a single exposure from that series:

[Click to galactinate.]

See? Brad calls this picture Second Chances. There’s the Milky Way, and all those stars. And the bright spot to the right is Venus, which made that brilliant trail in the first picture as it rose. If you have sharp eyes — and know your sky — you can spot a few other familiar objects in the sky: Deneb, Vega, Altair, and more.

But to me, in that first picture, perhaps the oddest thing is how on the left the stars appear to curve one way, and on the right they curve the other! Why is that?

It’s because Brad was able to see quite a bit of the sky at once. He was facing East when he took this shot, so all the stars you see here are rising. If you look off to the left, toward the north, you see the stars are circling the north pole of the sky (marked closely by the position of the star Polaris, which is off-frame here). Those stars appear to be moving counterclockwise. If you look to the right (south), the stars are circling the south pole of the sky, and appear to be moving clockwise! Why is that?

Think of it this way: imagine you’re in a car, driving on a road going through a forest. If you face left, looking out through the driver’s window, the trees appear to pass you from your right (the front of the car) to your left (the back of the car). Now turn around and look out the passenger window: trees move from your left to your right! Directions reverse because you’re facing the other way. The same is true for the sky, so while rising stars appear to move counterclockwise when you look to the north, they appear to move clockwise when you face the south.

For setting stars the directions are all reversed, but I’ll leave that to you to straighten out in your head.

Perhaps the hardest thing to explain to people about astronomy are the motions of stars and other objects in the sky. It helps, I think, to go outside and experience it for yourself, picturing yourself clutching the surface of a spinning ball as it moves through space. If you do that a few times, the motions become apparent, and start to make sense (as they have to!).

There is something beautiful about seeing all these movements and understanding them. It’s hard to put into words, but it’s a sense of completeness, of having all the parts fit together seamlessly and utterly, like cogs in a vast and layered Victorian clockwork mechanism.

But it’s better than that: it’s nature, and it’s all out there for you to see.

Image credit: Brad Goldpaint of Goldpaint Photography

Related posts:

Well, at least light pollution makes for a pretty time lapse
The stars above, the luminescence below
The lines in the sky are stars
Trailing the sky

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (11)

  1. BobG999999

    It made me think of this …

    Whenever life gets you down, Mrs. Brown,
    And things seem hard or tough,
    And people are stupid, obnoxious or daft,
    And you feel that you’ve had quite eno-o-o-o-o-ough,

    Just remember that you’re standing on a planet that’s evolving
    And revolving at nine hundred miles an hour.
    That’s orbiting at ninety miles a second, so it’s reckoned,
    A sun that is the source of all our power.
    The sun, and you and me, and all the stars that we can see,
    Are moving at a million miles a day,
    In an outer spiral arm, at forty thousand miles an hour,
    Of a galaxy we call the Milky Way.

    Our galaxy itself contains a hundred billion stars;
    It’s a hundred thousand light-years side to side;
    It bulges in the middle sixteen thousand light-years thick,
    But out by us it’s just three thousand light-years wide.
    We’re thirty thousand light-years from Galactic Central Point,
    We go ’round every two hundred million years;
    And our galaxy itself is only one of millions of billions
    In this amazing and expanding universe.

    The universe itself keeps on expanding and expanding,
    In all of the directions it can whiz;
    As fast as it can go, the speed of light, you know,
    Twelve million miles a minute and that’s the fastest speed there is.
    So remember, when you’re feeling very small and insecure,
    How amazingly unlikely is your birth;
    And pray that there’s intelligent life somewhere out in space,
    ‘Cause there’s bugger all down here on Earth!

  2. Keith Bowden

    Just one of the many reasons I come here daily. Thank you!

  3. Brian

    It can be even more breathtaking to imagine the earth being perfectly still and the entire sky rotating around it. (No wonder the ancients believed the earth was at the center of the universe.)

  4. Amazing images/video!

    The simplest way to explain the circular paths of the stars is to imagine you are standing inside a large sphere that is slowly rotating on one axis. The stars that are on the ‘equator’ of the sphere will move in a straight line. The stars to the right and left will curve around their respective poles. If you look at one of the poles you will see circular trails, like this:

  5. Relativity


    You figured all that by yourself? Or Phil engalactinated your poetic prose? Thanks

  6. As awesome as these rotating sky time lapse movies are at showing the results of a rotating earth, I’m curious why we never see a movie to show the effects of the tilt of the earths axis over a year?

    Any movies out there with the same observer Az/El taking a picture once per night at the same time?

  7. Messier Tidy Upper

    @5. Relativity :

    I think he’s referring to this :

    Via Monty Python.

    Fantastic video and photos and great write up too. Thanks Brad Goldpaint and BA. :-)

  8. Srikar

    galactinate. Love the term :)

  9. Keith Bowden

    @Brian (3)
    It’s funny, but the time lapse videos always look like what’s really happening, that the earth is spinning. It’s like a camera mounted on a rollercoaster – you know the ‘coaster isn’t sitting still with everything else whipping around. It just makes the reality that much more obvious when I look at these.

  10. j t

    Here’s a fantastic edit of the Paranal Observatory timelapse video.

    The sky stays stationary and the earth moves. We really are spinning!

    The original video. It’s great, too.

  11. I really appreciate you for stuff like this, Phil. And you’re right – closer to completeness is exactly what I feel when I grasp some new fact about reality.


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