Calculating a Moonrise Using The Photographer's Ephemeris

A sure-fire way to add excitement and emotional appeal to your images is to include a moon. There are two phases of the moon that I love to photograph - a full moon and a crescent moon (either waning or waxing). The trick is knowing where and when the moon will rise and set relative to your shooting position. If you are photographing a full moon, generally you would want to keep detail in the moon and match it to some detail in the landscape. You get two chances for this type of image per month - once when the moon is rising and once when it is setting. We will save that topic for another article. What I would like to discuss today is how to calculate any phase of the moon (rise or set) from your vantage point. The beauty of photographing crescent moons is that I don't worry about keeping detail in the moon - to my eyes, there is no detail. Thus, time of day (or night) becomes a moot point.

Recently I helped teach a spring Yosemite workshop with my friend and colleague, Gary Hart. I call Gary the moon expert as he usually designs his workshops to take advantage of some phase of a moon rise and/or set. He has an uncanny ability to calculate where and when the moon will appear (no easy feat with the high granite monoliths surrounding Yosemite Valley) and regularly gets his groups into position at the correct time allowing for them to create amazing moon images. I really can't explain Gary's technique for calculating moon positions, but suffice it to say it is a combination of knowledge involving: a compass, azimuth and altitude, checking moonrise and set times, and applying that information to a topo map. On the last morning of the workshop, Gary wanted everyone at the cars at 4:40 am (gulp) to get us in position at a location along Highway 120 looking back towards Yosemite Valley. From that vantage point, there is a narrow gap between El Capitan and Half Dome (two of Yosemite's most iconic monolith formations). Gary had calculated that a 4.8% waning crescent moon would rise between that narrow gap somewhere between 5:15 and 5:20 am! As you can see, almost on-schedule the crescent moon did appear and all that was heard was the clicking of shutters in the morning chill!

A 4.8% waning crescent moon rises between Yosemite's El Capitan and Half Dome. Canon 1DsMKIII, 300 mm at f/11, 4-seconds timed exposure, 400 ISO.

What resulted from all of Gary's careful calculations was a very cool image that everyone in the workshop nailed (at least I think they did)! I use a different method for calculating a moonrise/moonset using a software called The Photographer's Ephemeris. This software can be downloaded to your home computer and/or laptop for free, and is also available for the iPhone and iPad for a modest cost. I will refer to this software throughout this article by its acronym - TPE. Another friend and colleague of mine, Steve Loos, taught me how to calculate the moon's position relative to one's shooting position using the free version. I now demonstrate this technique at my workshops and will share the information in this article. It is really very simple but effective!

There are two basic pieces of information you must enter into the Photographer's Ephemeris. Part A involves dropping the main (red marker) pin onto the exact location that you are shooting from. As you can see, I marked my spot alongside Highway 120 where Gary had positioned his group. As best I can determine, the name of this location is The Half Dome Viewpoint. Here is TPE's rendering of our position.

The red pin marks the spot alongside Highway 120 in Yosemite and marks the groups shooting position. The light blue line shows the moonrise path relative to the highest peak in its path (see secondary gray marker). I used the Terrain mode so I could see the elevations of the various peaks along the route of the moonrise that would prevent me from seeing the moon. As you can see here, TPE told me that the moon would appear above the highest peak (elevation 11,000 feet) at 5:14 am and still be within the gap between El Capitan and Half Dome relative to the groups shooting position.

So how do I go about finding the highest peak in the moon's path relative to my shooting position? I simply enlarged the viewing screen of TPE and scrolled along the the moonrise line checking elevations of various peaks until I find the highest. Here is an enlarged view showing the tallest peak along the moon's rise path just above Vogelsong Lake in the Yosemite high country.

Once I found the tallest peak along the moonrise path, I simply dropped the grey marker (called the secondary pin) on that point. I then tapped the right arrow key on my keyboard until the moon's altitude turns from grey to black. In this example, I needed an altitude higher than my Apparent Altitude of +3.0 degrees, and as you can see, I got +3.1 degrees at 5:14 am.

Armed with this information, I went back to my RAW files and checked the first frame in my sequence where I did indeed see the moon. Because this moon was waning, just a faint outline of the upper right of the moon appeared at 5:18 am.

Look closely at bottom left of gap and you will see a faint outline of the moon (may be hard to see at this resolution but it is there). Remember this was a waning crescent so only the bottom-left of the moon is lit. I captured this frame at 5:18 am.

Now look at my next frame captured at 5:19 am!

Now the bottom-left lit potion of the moon begins to appear in the frame. The image that leads off this article was captured at 5:21 am. Remember, the moon is rising so it is moving on a track towards upper right from this position.

So The Photographer's Ephemeris told me I would see the moon at 5:14 am and I actually first spotted it at 5:18 am (but the tip of the moon - the unlit portion - moved into my frame at 5:17 am). It was three minutes off, but my exact positioning of the secondary pin may have been a bit off also, or I may have missed a peak that was in the moon's path that was just a bit taller. Personally, three minutes in miniscule; the bottom-line is that the moon did appear on-schedule and it resulted in not only an amazing image, but also an incredible experience for the entire group! As Gary told the group, This might just be the most beautiful sight on earth at this moment! I think we all agreed.

One thing that the group experienced was just how fast the moon moved across the gap (actually it was us moving and not the moon, but you know what I mean). The moon moves at a rate of .25 degrees per minute, or 1 degree every four minutes. This information is useful if one knows the angle of view of the lens they are using (relative to the sensor size). It is easy to Google this information. Suffice it to say, if you are shooting telephoto, the moon's motion becomes more of an issue than if you are shooting wide angle. At this time of the morning, I was shooting with an ISO of 400, an aperture of f/11, and needed a shutter speed of 4 seconds. There was a slight blur in the moon if enlarged to 100%. Of course, as the light brightened, my shutter speeds decreased.

I have just installed the iPad version of the TPE app and I also have a version installed on my iPhone. Both of these apps will cost $8.99 each but they are a great tool to help you calculate sun and moon rise and set times from any location on the planet! Here is a link to some tutorial videos that will help you use this software more effectively: The Photographer's Ephemeris Tutorial Videos.

I hope this article has helped you. Would love to hear your feedback!