Moon Shots, Charts and Alarm Clocks

By Jim Stroup, Virginia Tech

Be-da-deep. Be-da-deep. The sound of my alarm clock breaks the silence of the night. 
I open my eyes to see it’s 4:30 a.m. Instead of cursing the alarm for disturbing me so early, I leap out of bed with excitement knowing what’s in store for me. Peering out the window, I see the full moon hanging in the nighttime sky.

At dawn, I’ll be on the Virginia Tech campus to photograph the full moon setting. I’ve already determined where and when the moon will set, so all I have to do is show up at my predetermined location with my camera and tripod.

Allowing myself a half hour to get ready, I brew some coffee for the 40-minute drive to campus. I swing by my office to grab my gear and a university van – special license plates allow me to park anywhere on campus. Heading over to my location, I see the moon is just about ready to drop into the composition I’ve pre-visualized.

Photographing the moon either rising at sunset or, my personal favorite, setting at sunrise takes some preparation to predict where the moon will be and at what time it will be there, and a little bit of luck with the weather and cloud cover.

To start your planning, the first website we’ll look at is www.sunrisesunset.com. Print out a monthly calendar by clicking on the “USA” locations. Select your state and enter your town and the month you would like to print out. In the calendar options check the moon phases and the moonrise and moonset boxes. Click the “Make Calendar” button. This will give you sunrise and sunset times along with the moonrise and moonset times and the moon phases. I look for times when the moon is rising just before sunset or setting just after sunrise. This usually occurs near the full moon, but you can also catch the crescent moon at these times.

Now we’ll go to the U.S. Navy’s website, www.usno.navy.mil/USNO/astronomical-applications/data-services/alt-az-us, to find the altitude and azimuth of the moon. The altitude is the angle up from the horizon, with 0 degrees being on your local horizon and 90 degrees being straight up. The azimuth is the angle along the horizon, with 0 degrees being true north. The Navy likes to make us think. While the sunrise/sunset calendar will print out in AM and PM and account for daylight-saving time, the Navy’s site uses a 24-hour clock and doesn’t account for daylight-saving time, so you’ll need to add one hour to the times when daylight-saving time is in effect.

On the Navy’s opening page, select the moon, the year, month, and day you want to photograph. I change the tabular interval to 15 minutes instead of the preset 10 minutes.

Then type in your town, select your state and hit the “compute table” tab. Your table will give you the moon’s altitude and azimuth in 15-minute intervals. A break in the output table means the moon is not visible until the next indicated time.

In Blacksburg, VA., the moon’s azimuth will change about 60 degrees during the year for both moonrise and moonset. The moon sets in June around 240 degrees and drifts north to about 300 degrees in December. Moonrise varies from 120 degrees in June to 60 degrees in December. Knowing these azimuths, along with some patience and planning, will help you in determining if the moon will rise or set in a favorable place on campus.

To predict where the moon will rise or set, you’ll need a compass or a smart phone with the compass app. I like the app on my iPhone, which allows me to set it for true north. A standard compass relies on magnetic north, which varies from true north by as much as 30 degrees in North America (it’s eight degrees in Blacksburg). The Navy uses true north, so if you’re using a standard compass, you’ll need to find the declination for your area by linking to the NOAA’s Geomagnetism Data Center and adjusting your compass to allow for the declination.

Now we’re ready to scout suitable locations. With a compass and the altitude and azimuth charts in hand, I search for locations that let me use as long a lens as possible with some room to move left or right as the moon courses through the sky. You can approximate how high the moon will be from the azimuth chart. I’ll generally shoot when it’s below 30 degrees. The compass will give us an accurate prediction of the moon’s future location. It doesn’t rise or set straight up and down, but will track at an angle that moves left to right.

It’s also good to check the weather forecast. I use Accuweather.com. The satellite and radar imagery shows both the cloud layer and radar combined. The site also has a feature to see the cloud layer’s movement over the past 90 minutes or so. I’ll use this movement to extrapolate where the clouds will be in six to eight hours. By comparing this with the hourly forecast, I can make a fairly accurate guess as to whether or not it will be clear when I want to be out photographing. Remember, the moon is on the horizon, so it’s OK if there is a cloud layer above you as long as it is clear on the horizon. This can make for some epic conditions for photography.

Balancing the exposure between the bright moon and the twilight hours can sometimes be tricky. The moon’s exposure is basic daylight, 1/ISO at f16. On the East Coast, as the sun moves closer to the horizon, the moisture in the air decreases this exposure, which works in our favor. If you’re using the camera’s auto exposure mode, you’ll want to underexpose the scene by one to two stops. This will darken your foreground subject to give you more a more accurate dusk or dawn appearance and will help hold detail in the moon’s surface. Gradient filters will help balance the exposure, but these only work if you have a horizon that is a fairly smooth line.

With the right amount of planning – and a little bit of luck – you can get a shot that will make you glad didn’t roll over when that early alarm clock went off.

Jim Stroup has been the University Photographer at Virginia Tech University since 2008, following a freelance career in photography that began in 1982.