Many photographers enjoy shooting the sun, moon or galactic centre positioned behind a building or other man-made object. Photo Ephemeris Web Pro provides tools to make it easy to plan such shots. Let's work through some examples.
Note: you should be familiar with both Geodetics and Visual Search before trying to complete this tutorial. The apparent height and target height features discussed in this tutorial require a Pro subscription. Please consider upgrading if these tools will help your photography planning.
Glastonbury Tor and St. Michael's Tower
Imagine we would like to find dates when we can photograph the moon behind St. Michael's Tower, on top of Glastonbury Tor in England.
Wikipedia, By Eugene Birchall, CC BY-SA 2.0
I've never visited this location in person, so I'm doing all my planning online using resources on the internet together with Photo Ephemeris Web.
You already know how to find dates when the moon will sit behind the top of the Tor - that is the ground level at the high point shown in the photo, but how do we allow for the height of St. Michael's Tower?
What is the height of St. Michael's Tower?
For many famous buildings you won't need to do this next step, as building heights are usually easily found online.
The first thing we'll need to know is the height of the tower. I've scoured the internets and can't find it documented anywhere. I'm sure it's sat there in some dusty manilla folder stashed in a drawer somewhere in Somerset County Council's offices, but in the absence of that, let's get an estimate from the photograph itself, together with the geodetics tools in Photo Ephemeris Web.
Helpfully, Wikipedia includes the coordinates of the shooting location used in the photo above: (51.130206, -2.710349). Putting those into Photo Ephemeris, and placing the Geodetics pin on the tower (link), we obtain an elevation difference of +151m from the shooting location to ground level atop the Tor:
Note: we're using Google's elevation service for this tutorial - other sources significantly underestimate the height of Glastonbury Tor. (Also, the 'Tor' is the hill - not the tower.)
Doing a little elementary measuring (using xScope), we can guesstimate the height of the tower. First measure pixels from where the ground just starts to rise to the top of the Tor: 672px on my screen (absolute numbers don't matter - only relative). (And, yes, there are better methods than this!)
Then we measure to the top of the tower: 748px
A rough estimate of the height of the tower is (748px - 672px) × 151m/672px ≈ +17m. I would guess that's within ±2m of the right value. You can use a similar estimating technique on other photos to confirm/refine your result. We'll go with 17m for now.
Apparent Height of the Moon
Before we jump into using Visual Search to find dates/times, let's first set up our shooting position and look at how we can estimate how high above the tor the moon will appear.
You may have noticed from the screenshot above that our reference photo is taken looking north. We're never going to see the moon quite in that direction (remember, in the northern hemisphere, very broadly speaking, it rises to the east, transits to the south, sets in the west), so let's find a different shooting location to work with that will provide a broader range of options.
A spot in the fields to the west of the Tor will do (link):
Checking out a few dates at random, and we find that moon crosses the line of sight from red to gray pin on many occasions. When Geodetics is enabled (as shown above) there's an additional option in the altitude chart legend that allows us to view the apparent height and size of the moon (or sun):
When enabled (click again to toggle it off), you will see the following two data points:
- Apparent height: the apparent height of the moon above the ground at the gray pin, as viewed from the red pin
- Apparent size: the apparent size of the moon (height/width) at the distance of the gray pin from the red pin
At this particular date/time, the moon appears +100m above the gray pin, i.e. around 5 times the estimated height of St. Michael's Tower (~17m):
The apparent height/size display provides a way to research dates and times when the moon might be at a desired height. However, as you might have guessed, Visual Search provides a much quicker approach.
Using Visual Search with Target Height
Switching to the 3D Sphere page and enabling Visual Search, we can use our estimated height to have Photo Ephemeris find dates when the moon will appear centred on the top of St. Michael's Tower. Here's how you do it.
- Switch to the Sphere page
- Enable Visual Search
- Set Body to Moon
- Set Duration to 5 years
Next, because we have a very specific alignment of the moon in mind, we're going to set up our Visual Search Target in a particular way:
- Uncheck Range
- Set Tolerance to 1° (roughly twice the moon's angular diameter)
- Click Use geodetics
- Set Target height (m) to '17'
You may have noticed that, as you entered 17 in the Target height field, the target Altitude changed from ~10.4° to ~12.7°.
Now we're ready to search. If you have things set up as above and start your search from Feb 5 2022, you should see 22 results. Choosing the second one, Thu March 3, 2022, we see the following:
You can see that the moon is higher than the terrain at the secondary gray pin location. It is at the exact apparent height above the ground that we asked for, 17m:
Filtering the results for full moons only, you obtain only one result over the 5 year period from Feb 2022. Set your calendars for 24 Sep 2026 for a nautical twilight full moon behind the top of St. Michael's Tower on Glastonbury Tor:
Full moon behind the Chrysler Building
Imagine you'd like to photograph the full moon rising behind the Chrysler Building in Manhattan. Maybe something like this wonderful shot by Fred Greco:
Credit: © Fred Greco, All Rights Reserved. Used with permission.
We're going to be shooting Manhattan from some distance away in West Orange, New Jersey, where there are good views of the New York City skyline. The distance (around 14 miles) will require use of a long telephoto lens, which in turn will mean the moon will appear large next to the buildings.
Our objective is to use Photo Ephemeris Web Pro to identify dates when the full moon will be rising in the right alignment and with good lighting conditions, i.e. around sunset.
Map Pin Placement
If your subject is illuminated by the sun or moon, then you will typically set the red pin there. However, in this case, the moon is going to be in the shot itself, so the red pin will be our shooting location and using the geodetics tool, we'll place the grey pin on the Chrysler Building:
Let's switch to the 3D Sphere page to enter some details for the Chrysler Building. The height of various features of the building is readily found online, so there's no need for estimation tricks in this example.
To enter the building height and footprint size, click Edit in the Geodetics panel (make sure you're on the Sphere page first):
You'll see a form where you can enter elevation offset values for each pin, and, as we're on the Sphere page, a building footprint size. The height of the Chrysler Building is 1046ft, according to Wikipedia. And a little measuring using the Geodetics tool on the map suggests the width is around 200 feet. Let's enter those values:
We'll leave the red pin elevation offset at +5 feet - that's around the height of the tripod. It makes only a very small difference to the shot alignment, so don't worry about being overly accurate here. As we're not entering any sort of building height at the red pin, we can also leave the building footprint size at the default of 328 feet (100m) - you won't see it anyway.
Click Update (the calculated values shown in the form will update), and then Close the form.
Note: you can use elevation offsets to represent building heights, or to make a correction to the elevation determined by the app (e.g. to adjust the given elevation of a mountain), or a combination of the two.
Visualizing Building Height
If the grey pin lies outside the bounds of the Sphere, click to zoom out at the lower right. You should see something like the following:
Adjust the camera position (click and drag, plus pinch to zoom on my trackpad), you can get a closer view of the grey pin on the Chrysler Building to see the effect of setting the building height and footprint size. We now have a scale model of a generic tall building at the grey pin location:
Visual Search Parameters
Next, we'll configure Visual Search to find dates when the full moon will rise behind the building, as seen from our shooting location in New Jersey. Here are the default parameters in the Visual Search page - we're going to want to change them:
Here are the changes we need to make:
- Body: change to Moon
- Duration: change to 5 years (recommended minimum for moon searches is 2 years)
- Uncheck 'Range' - we're going to use a specific target azimuth and altitude
- Under Target, reduce Tolerance to 0.4 degrees (we'll see why below)
- Click Use Geodetics
Your Visual Search form should now be similar to the following:
You can see that the Visual Search target area is now aligned with the top of the Chrysler Building. Because we entered an elevation offset (the building height) for the grey pin, when we clicked Use Geodetics, it set the target to the top of the building. You can also see that the target area above (the blue square mid-air in the screenshot) spans just either side of the building. It appears in front of the building closer to the red pin due only to the map zoom level and pin placement - that makes no difference to what the app will search for.
Looking back at Fred's shot above, you can see that the moon is not actually centered on the top of the building though - it's below that. Checking Wikipedia, we see that the roof height of the Chrysler Building is 925 feet. My guess is that the moon is centered at about 972 feet in the shot, so let's enter that as the Target height:
Notice that the target Altitude has reduced from 0.2657° to 0.213°, reflecting the lower target height.
OK, now let's search (I'm searching from Jan 23 2022 - you may get different results if your start date is later):
We obtained 13 results - not bad. Clicking the first of these, we can see that the alignment is well-nigh perfect. However, this is in the middle of the day (see the shadow from the building in the screenshot) and the moon is only ~11% full.
We really want a full moon around sunset, so let's filter our results to see if we have any matches. Click on the Filters tab, and then from the Suggested filters, choose Full Moon and Near Sunrise/sunset:
Click to Apply the filters, and we are left with only one result, Aug 27 2026. Let's click on it to view the alignment:
You can see that the moon is in the target zone, although centered just slightly to the left (from the photographer's perspective) of the Chrysler Building.
If you choose 1× for the body size (drop down located just above the sphere) then the relative size of the moon and the building are accurate. You can see that the moon will appear large relative to the building, as it was in Fred's photo above. Even though the center is slightly to the left of the building, the moon will still 'span' the tower. And just 2 minutes later, 7:30pm, it will be centered on the building, albeit sitting a little higher than the top.
It's usually easier to check these details by 'flying' to the grey pin - from the red pin, everything will look tiny. And also, don't worry that the moon appears closer to the red pin than the Chrysler Building. Obviously, that's not reality - it's just a side effect of the map zoom level we need to use for this particular shot.
One final sanity check - let's circle back to the Apparent Height data that we looked at in the Glastonbury example above and check what the apparent height of the moon is for our Aug 27 2026 example. With the altitude chart displayed, click the icon at the top right of the legend to display the Apparent Height data:
The moon's apparent height is shown as -69ft. That sounds odd. But remember, this is relative to the geodetics results, which account for the building height of 1046ft that we set earlier. The center of the moon appears 69 feet below the top of the Chrysler Building, which seems reasonably consistent with Fred's photo.
UPDATE: v2.7.11 changes the behaviour of the app to always show the apparent height above the ground, rather than relative to the grey pin height. Therefore in this example, you will now see the apparent height of the moon displayed as 977ft (i.e. 1046 - 69). We'll update the screenshot above soon.
Important considerations for planning your building alignment shots:
- Check your elevations: be sure to double check the elevations the app is using for both primary and secondary pins. You may want to try changing the elevation source if the numbers don't seem correct.
- Obvious, but double check your building or object height! If you don't have a reliable data source, a scouting trip to the location is advisable.
- Double check the maps: if you try different map styles for Glastonbury Tor, you'll see they don't agree on where St. Michael's Tower is actually located (at the time of writing - maybe it will be fixed eventually). It seems to be some sort of calibration or registration issue - maybe caused by an incorrect adjustment for the zenith angle of satellite imagery?
- Pin placement is critical: even a few feet of mis-positioning can throw your planning off. Double check everything.
- Need a bigger moon relative to your target building? Move farther away and use a longer lens. Apparent size increases with distance - counterintuitive though it sounds.
- You can (and should) adjust your shooting location. The example above considers only a single position for the red pin, but it's in a field: you can move around. And if you're shooting from a distance with a long lens, you'll want to stay flexible to maximize your shooting window.
- Things move fast: it's amazing how quickly the sun and moon seem to move just when you'd rather they remained still. Be prepared!
Finally, remember that you always have a choice of approaches to your planning.
Either you know when you want to shoot (e.g. the evening before the next full moon) and need to work out where to be, or you know your shooting location, subject and what conditions you want (e.g. the Chrysler Building example) and need to know when you can get the shot.
If you know when but not where, use maps, geodetics and apparent heights to see what's possible (e.g. compare the apparent height of the moon with your target building for different shooting locations).
If you know where but not when, use Visual Search to find the upcoming shot opportunities.
Do you have suggestions on how we can improve this? Let us know using the Help widget on this page!
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