Planning a lunar eclipse composite at the Washington Monument

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I wish I could be there to try this out, but I’ll be in Colorado, not DC, on Monday night.

As you probably have read by now, the night of Monday/Tuesday 14-15 April 2014 will see a total lunar eclipse, the first of four that will occur between now and the end of 2015.

I’ve added a couple of other posts on the site about this upcoming upcoming eclipse which you can find here and here.

Washington Monument

In this final installment, we’re going to use TPE for iOS and its sister app, The Photographer’s Transit, to make a plan for a composite sequence of the eclipse happening behind the Washington Monument in DC. If you don’t know it, the Washington Monument is a 555 ft (169m) tall obelisk that stands in the National Mall in DC. A quick Google search reveals that shooting the moon behind this structure is a highly popular activity!

The plan will be to position the Washington Monument in the frame such that we can capture multiple shots of the moon without repositioning, and then combine them appropriately in post production to generate a single composite image showing the progression into and then out of total eclipse. We’ll need to find a shooting location and suitable lens selection to achieve this.

Let’s get started. First thing we need is the timing information for the eclipse, which, as before, we can get from NASA’s page :

EventTime (UT)
Penumbral Eclipse Begins:04:53:37 UT
Partial Eclipse Begins:05:58:19 UT
Total Eclipse Begins:07:06:47 UT
Greatest Eclipse:07:45:40 UT
Total Eclipse Ends:08:24:35 UT
Partial Eclipse Ends:09:33:04 UT
Penumbral Eclipse Ends::10:37:37 UT

Translating these times to UTC-4 hours, we can see that the penumbral eclipse starts at 00:53 on Apr 14, and ends at 06:37. From TPE, we can see that moonset occurs at 06:38 on Apr 14, meaning that we in theory, we could capture the entire sequence. However, the sun also rises at 06:31, which would mean we would have to deal with going from darkest night to brightest day in our composite, which could be rather difficult to achieve convincingly.

If instead, we plan on shooting until just after the end of partial eclipse, the light levels will be much more manageable, and we still capture the most dramatic phases of the eclipse event. Partial eclipse ends at 05:33, just after the start of Nautical twilight, when the sky will still be a deep, dark blue.

So, shooting from, say 5 minutes before until 5 minutes after partial eclipse gives us the following range of times and moon positions:

EventTime (UT-0400)AzimuthAltitude
Partial Eclipse Begins -5 mins:01:53195.9°39.3°
Partial Eclipse Begins:01:58197.5°39.0°
Total Eclipse Begins:03:06216.2°33.0°
Greatest Eclipse:03:45225.7°28.0°
Total Eclipse Ends:04:24233.6°22.4°
Partial Eclipse Ends:05:33246.1°11.1°
Partial Eclipse End +5 mins:05:38247.0°10.1°

You can use the time slider and details panel in TPE to obtain these figures. It’s also possible to get a sense of the moon’s motion by sliding back and forward while observing the azimuth and altitude indicators:

TPE screenshot

In order to capture the moon during this timeframe, our field of view will need to accommodate:

  • The Washington Monument (narrow, but tall)
  • The moon’s lateral motion from +195.9° to +247.0° (change in azimuth)
  • The moon’s vertical motion from +39.3° to +10.1° (change in altitude)

From TPE, we can see there are a couple of possibilities for shooting location:

  1. East north-east of the monument (with the monument at the right of the frame), so that the moon “falls” towards the foot of the monument
  2. North of the monument (with the monument to the left of the frame), so that the moon starts out towards the top of the monument and “falls” the lower right corner of the frame

Instinctively, I like the feel of the second option more:

Photo plan sketch

So, now we need to determine an appropriate shooting position and camera/lens selection to capture this shot. We can use Photo Transit to help us get some answers.

We’re going to need a horizontal field of view of at least (247.0-195.9) = 51.1° just for the lateral motion of the moon, and at least (39.3 – 10.1) = 29.2° for the change in altitude. We identified five distinct times in the table above, which will correspond to the moon in different positions in our final composite image. The Washington Monument itself will be a sixth item. So, to determine an ideal horizontal field of view, we should add another 20% for the monument, and a further 20% as margin so our subjects aren’t hard up against the edge of the frame. Hence: 51.1° * 140% = 71.5°.

Using a full frame SLR, such as a Nikon D800, Photo Transit shows us that a 25mm focal length will give us what we need, assuming a horizontal composition:

TPT screenshot

While it would be nice to use a longer lens to capture the moon so that it is larger in the frame, the fact of the matter is that for this shot, the degree of movement over the few hours of the eclipse is too great. A telephoto lens would simply have too small a field of view to capture the moon without repositioning between shots (which would rather defeat the purpose of this plan – although I suppose you could always do a multiple shot panorama and stitch it back together afterwards; getting the geometry right would be a challenge though!).

The next question is to determine where we should stand to ensure we can capture the full height of the Washington Monument. Using Photo Transit’s elevation profile features, we can specify the height of the object at the subject location (560 feet or thereabouts):

TPT screenshot

This shows that with our camera set to 25mm we won’t capture the top of the monument without some adjustments. So let’s tilt the camera up and check that we can capture the full height of the object in the frame:

TPT screenshot

Good – we can now see that by tilting the camera up to point to around +20° we will have the full height of the monument in our shot.

The final step is to adjust the subject position to place the monument to the left of the frame. As a sanity check, we can confirm that the field of view will capture the end of the eclipse. From the table above, the moon will end up at +247°. Our camera is pointed at a bearing of 216°, and has a horizontal field of view of 71°. That puts the far right of the frame at (216 + 71/2) = 251.5°, so we know the moon will remain in the frame for this shot:

TPT screenshot

So, we have a plan. All that remains is to pack the spare batteries (it’s a long shoot) and the warm coffee and head out for an overnight shoot on Monday. If anyone is able to have a go at this, I’d love to see the results!

You can view the shot plan we developed using Photo Transit here: http://phtrns.it/1qPOOR4

*****

Postscript: of course, it often pays to check the weather forecast too. I’ve just had a look, and it isn’t looking great for DC :(

Happily, however, the techniques we used apply globally, so go have fun making your own eclipse shot plans!