Rules for Shooting the Sun and the Moon


Photography is impossible without light and most light comes from the sun.  Therefore, a few things about the Sun are useful to know.

-       A circle has 360 degrees.

-       A complete turn of the Earth takes about 24 hours.

-       For the Sun to appear in the same part of the sky from one day to the next it has to appear to make a complete circle of 360 degrees in the sky around the observer.

-       360 degrees divided by 24 hours yields an answer of 15.  That means the Sun appears to move in the sky 15 degrees each hour.

-       The apparent size of the disk of the Sun as seen from Earth is about ½ of 1 degree.  Divide 360 by ½ to get an answer of 720.  So the Sun must move its apparent width 720 times before it appears in the same place in the sky.

-       There are 1440 minutes in a 24 hour day (24 x 60).

-       Therefore, and this is the whole point of this exercise, the Sun moves its apparent width in the sky every 2 minutes (divide 1440 by 720).

 

-       Much of the above is true for the Moon.

-       The apparent size of the disk of the Moon as seen from Earth is also about ½ of 1 degree.

-       The Moon circles the Earth about every 28 days.  Divide 28 by 24 (24 being the hours in a day) and you get 1.167.  Drop the one and the remainder is very close to the 15 degree hourly number shown above.

-       This means the Moon will appear more easterly in the sky roughly 17 degrees, or a little more than 1 hour equivalent every day.  The moon moving in its orbit appears to us to be in a different place each night we observe it.  Our relative position to where the moon is lit by the sun has changed so the phase of its being lit has changed.  This change of position is why a different crescent or phase of the moon is seen each night.

-       A new Moon or a new crescent moon is almost half a sky (180 degrees) away from a full moon.   That means from our viewing point it is very close to the sun.  That is why it is very hard to get a photo of a new crescent, because it appears so close to the sun.

-       Keep the phases of the Moon in mind, and this is the whole point of this Moon thing.  The best time to photograph a Moon is often when it is a few days away from full because it is rising about the time the sun is setting.

Another thing to know about the moon is how much of the sunlight hitting it is reflected back to us on Earth.  That reflectance, or albedo, varies by a number of factors.  These include the phase of the Moon, the variable distances of the Earth, Moon & Sun from each other, how clear the atmosphere is between you & the Moon, & how high the Moon appears to be above our horizon.

The average amount of light reflected back at Earth from a full moon is about 12-15%.  The 1st & 3rd quarters are about half or less than that depending on the visual factors in your viewing area.

Why do you need to know this?  Some of you may want to make long exposures at night.  If you do then moonlight will affect your image.  If your exposure is long enough the Moon will bathe your exposure with so much light the landscape will look like it was shot during the day.

Of course most often we want to make short exposures of the landscape with the moon in it.  In those cases we hope the contrast of the moon and the landscape are both within the range that our film or digital sensor can capture.

Here is one I am pretty proud of, Ancient Bristlecone Pine and Moon shown below and elsewhere in this website.

So the question becomes what is the proper exposure for the moon?  The short answer is it varies because the reflected light from the moon varies.  If you are shooting in day light, dawn or dusk a reading from your meter will usually render a properly exposed landscape and a moon with detail.

If you are shooting at night things change considerably.  Remember, the moon is no larger than ½ of 1 degree!  Most moon phases show smaller than that!  That means your in camera spot meter can’t evaluate the moon without being overly affected by the night sky around it.  The same problem holds true with a 1 degree spot meter because the 1 degree area is too large!

A full moon about 1/3 above the horizon on a reasonably clear, dark night will give you an EV of about 14.667.  That means if you have your ISO set at 200 & your f stop set at f/16 then your exposure should be about 1/200th of a second.  This should give you a moon with lots of detail, and a foreground (the landscape here on Earth) best described as a silhouette.

Remember, photography is a trade off.  At night you can’t get an illuminated landscape and a detailed moon without lots of tricks.

Another good time to photo the moon in a landscape is around dusk or twilight.  The color of the sky can still be interesting, even spectacular.  The foreground may have some illumination, or may become a silhouette, and the moon can be sharp and well defined.  It is usually best to expose for the color of the sky.

That leads to another point.  The moon is moving, that was explained above.  Where does the exposure change from a moon with sharp edges to a moon that is blurring across the sky.

This answer is dependent on the focal length of your lens.  The longer the focal length the shorter time you have.  A longer focal length lens magnifies your scene.  The moon takes up more space in your frame and therefore appears to move across the frame more quickly.

There is a rough formula for this.  Take the length of a normal lens.  In 35mm photography that length is generally considered to be 50mm.  Take the actual length of the lens you are using.   It can be anything, but lets say it is 135mm.  Divide 50 by 135.  Take your answer and multiply by 5, then take the same answer and multiply by 10.  This is your range of seconds where the moon will appear to be stationary in your frame and not move or blur on your film or digital file.

The formula means the shorter the lens the longer the exposure you can get to give a stationary moon.  The trade off is the shorter the lens the smaller the moon will be in your photo.  If you want a wide angle shot with a large moon it means you will have to overlay a moon into your landscape either digitally or via double exposure.

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