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Saturday, January 12, 2013

Best Time to Photograph the Starry Night Sky

The Starry Night Photo Window: 2 hours after sunset & 2 hours before sunrise (click for larger view)
The best starry night skies are found two hours after sunset and two hours before sunrise. Photograph anytime before or after this window, and there is enough twilight to compete with starlight.

Fudging even 15 to 30 minutes outside this window can greatly lower the quality of your star photography. That's because daylight is 40 million times brighter than starlight, and even a little left over in the twilight sky can be overpowering to all but the brightest stars! Although this twilight may be imperceptible to the eye, it will lower the contrast of your night sky and dim the weaker stars, as in the example below. In this photo, the sun set on the right side, 1.5 hours ago, and a crescent moon is just now setting on the left side —but it is the leftover twilight from the sun that is competing the most with the stars:

Moonset over Teton Range & Jackson Lake — 1.5 hours after sunset ~ © Royce Bair


Only the brightest stars are able to compete with this twilight sky and the setting moon. Very little of the Milky Way, on the left side, is distinguishable. Although this is a beautiful photo, these are not optimum conditions for the most brilliant starry sky photos.

Milky Way over Teton Range & Jackson Lake — 2 hours after sunset / no moon ~ © Royce Bair
Sunrise and Sunset Times: There are many website and applications available to find these times for any given location, but one of the most convenient and reliable is one from the U.S. Naval Observatory website. With this site, you can enter a location and obtain a table of sunrise and sunset times for the whole year of your choosing.

Other competition for darkness: Moonlight should also be avoided, since it is at least 135 times brighter than starlight. Even a thin, crescent moon is five times brighter than starlight! Man-made light pollution should also be avoided where possible. (Both of these competitors will be discussed in greater detail through other posts.)

Royce Bair is the editor of this blog and the photographer of the above images. Here is my gallery of NightScape images. My schedule of workshops, tutorials, and other events is available here.

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6 comments:

  1. Good read, but shouldn't the headline "best time to photograph the starry night sky" be in the middle where the stars are? And not on the left over the sunset? The first time I read it I thought you were saying that two hours before or after sunset is optimal, but after rereading I believe your mean BETWEEN two hours after and two hours before? So four hours is as good or better than two hours...
    Thanks!

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    1. Thanks for the comment! I've changed the title at your suggestion, and added some text to the lead photo: "< Best time for starry night sky photos >"

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  2. Hello Royce, is it fair to say that the 2-hour-rule is more of a general guideline than a precise rule? One could always wait for the end of the astronomical twilight (which doesn't necessarily come after 2hrs) and be certain to get the best sky (provied the the moon is not around), am i right?

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  3. The best time depends on your latitude as J. Carpenter is asserting. I was surprised how quickly darkness falls near the tropics - specifically on the Big Island in Hawaii which is at 19 degrees latitude compared to my normal Northern California experience at 37 degrees. 90 minutes after sunset up here is usually sufficient.

    Astronomical twilight ends tonight at 18:46 an hour and 30 minutes after sunset at 17:15. But in Hawaii, sunset is at 18:04 and Astronomical twilight ends at 19:21... that's 10 minutes sooner at this time of year. But in the summer, darkness comes yet another 10 minutes sooner after sunset. In Calgary, Canada it takes almost two and a half hours after sunset to get to complete darkness during the summer and two hours during the winter. Of course if you go far enough north (like Fairbanks, Alaska) or south you can find places that never get out of Civil twilight during their summer. Indeed, in Fairbanks, Alaska, there are only two hours of complete darkness per night in April.

    By the way, the definition of Astronomical twilight is the period at which stars are visible, but things like nebulae and fainter galaxies are not.

    http://en.wikipedia.org/wiki/Twilight#Astronomical_twilight

    I use The Photographer's Ephemeris to determine these times. Great tool: photoephemeris.com

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  4. Always looking for more tips. Enjoyed reading the comments also-- very enlightening.

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