Moon over Miami - wait, no, over New Orleans
July 20, 2010 7:01 PM   Subscribe

Astronomers: how to best determine the exact time to take a photograph of the full moon where the moon is situated between two earthly objects?

I live in New Orleans. A while back I took this photo and while I like it, I would have loved it had the moon been lower in the sky. Specifically, I would have loved it to be between the two skyscrapers in the middle of the photo (Place St. Charles on the left and One Shell Square on the right).

Here's what I can tell you: I was shooting from the Broad St. overpass above the Pontchartrain Expressway. I do not know the height. I don't even know how much that would matter. I do know the locations of Place St. Charles and One Shell Square, and I do know that the building between the two of them (the more rightmost in my photo, the one with the red light on top of the antenna) is the World Trade Center of New Orleans listed at 407 ft. high, so the moon would have to appear higher than that.

Here's a map to the full setup as best I can tell, showing the shooting location, the two buildings between which the moon should reside, and the location of the building over which the moon should appear.

So, astronomy experts, from the limited information I've provided can you tell me when (or if at all) the full moon will ever appear exactly between those two buildings?

A little lagniappe: here's a time-lapse video of the moon rising over downtown New Orleans, shot from the same location.
posted by komara to Science & Nature (14 answers total) 2 users marked this as a favorite
You should use the program Celestia to examine your original conditions. I would think that when you are near the date you took your photograph at the very minimum you should be able to get close to the original view, and in fact depending on the time of year it may be possible several times to duplicate it more or less exactly on the half and quarter days (IE 90 and 180 days away from the original date).

The moon looks full for a more than one evening, maybe two or even three.

If you aren't too proud to take a photographic tip, you may want to look at the moon itself. Notice that there is no detail in the moon, as it is overexposed beyond the dynamic range of the camera. It's a tough situation for sure, because if you expose for the surface of the moon (basically sunny f/16 rule because it's in full sun) in order to get the surface details, you won't see much of the city skyline.

I have attacked this problem with HDR photography, bracketing exposures. I have also sometimes taken a single RAW file, which was exposed to leave some texture in the moon, and cranked up the shadows but this may look awful on your camera.
posted by Sukiari at 7:19 PM on July 20, 2010 [1 favorite]

Response by poster: Sweet, Celestia is available for Mac OS X and is free. I'll have to check it out.

As for the original photo, trust me, I know the moon is blown out. I don't mind the tip. If I thought it was a great photo I'd not be worrying about re-taking it, ha ha. I'm pretty anti-HDR for my own stuff. I'm hoping to find a time when the moon is between the two at sunup or twilight in order to get a better exposure. However, if it turns out the nearest time is full midnight, so be it. I'll still end up exposing off the buildings more than the moon itself.
posted by komara at 7:37 PM on July 20, 2010

HDR Doesn't have to look all blown out and funky color saturations. I've tried some similar (moon + skyline) type shots, where the moon was exposed properly in a second shot, then put the two together.
posted by defcom1 at 7:57 PM on July 20, 2010

Response by poster: Looks like Celestia is out. It has great stuff, but the Earth's surface (as far as I can tell) is insufficiently fine-grained to be able to mark such detailed locations.

I hadn't taken a serious look at Google Earth in a while and therefore hadn't realized how many incredible .kmls people have made for it. I think I'm in the process of tracking a decent moon phases over time overlay ... maybe.

defcom1: I've made spot adjustments to exposure in various parts of images, and that's fine. HDR as a process still isn't for me.
posted by komara at 8:09 PM on July 20, 2010

However, if it turns out the nearest time is full midnight, so be it.

If you shoot a full moon as it's rising, it will be as the sun sets. That's just the way it works.

The day before full, it will rise about an hour before sunset, giving you more light on the buildings. The day after full, it will rise about an hour after sunset, giving you more darkness.

There's a full moon about once a month. The next one is Sunday, July 25, and the moon will rise at 7:47 pm in New Orleans. (There's a neat online calculator here.)
posted by exphysicist345 at 8:48 PM on July 20, 2010 [2 favorites]

Why not determine the exact coordinates of the bridge from Google Earth, then plug those into Celestia by typing them into the box?
posted by Sukiari at 9:19 PM on July 20, 2010

You can also use Stellarium (which is free) - screenshot.

With a bit of care, I was able to match it to a location I took a old photo from, and then used it to determine the day (and time!) that I pulled the shutter and took that photo, based on what was in the sky.

So it will work for what you want it to do. But for it to do so, you'll have to take an good compass measurement of the angle to those buildings, or else add your own horizon photographic overlay that includes the buildings, because you are trying to find when the moon is in a certain spot in the sky, and it sounds like you don't yet know where that spot in actually is without the buildings as a reference point. (eg so you could add the buildings to software, or take measurements so you don't need the buildings. Or, of course, continue looking into whether Google Earth will show the buildings relative to the moon for you)
posted by -harlequin- at 9:26 PM on July 20, 2010

Best answer: There is a free Adobe AIR program (and also paid iPhone version) called the Photographer's Ephemeris that sounds almost exactly like what you want. Given a location on a map and a date it will show you graphically the direction that the sun and moon will rise and set, as well as what the phase of the moon is.

It's great for figuring out those "city-henge" times.
posted by cftarnas at 9:31 PM on July 20, 2010 [1 favorite]

Use Google Earth in Sky mode! It seems to have 3D models of the two buildings in question and the local terrain, so you won't have to manually figure out the building locations and heights like you would with a sky-only program like Stellarium or Celestia.
posted by miyabo at 9:37 PM on July 20, 2010

Response by poster: exphysicist345:
If you shoot a full moon as it's rising, it will be as the sun sets. That's just the way it works.
Lord, but I feel I'm missing something here. Is that true? I must have skipped the class in junior high where they taught us this. Am I missing some other fundamental idea, like "the full moon always rises over the same spot on the horizon" or something else? I thought this was totally variable. Obviously I have never studied astronomy.

Why not determine the exact coordinates of the bridge from Google Earth, then plug those into Celestia by typing them into the box?
I could get the coordinates for the spot for the photo taking, but without another visual reference like the buildings downtown I couldn't tell if I had the earth rotated 1 degree off or 10.

-harlequin-, cftarnas, miyabo: thank you very much for the suggestions. I will definitely have to check those out. I am especially interested in Google Earth in Sky mode - I must have missed that last night when looking through stuff.
posted by komara at 7:38 AM on July 21, 2010

Response by poster: cftarnas, please show up to collect your prize. The Photographer's Ephemeris gave me exactly what I wanted within about 30 seconds after installation. I now have two dates in the near future (one only 5 days away!) where the moon should be more or less totally full and rising between those two buildings. Of course I'll need a little bit of trial and error to see how much it moves to the side before it gets high enough to clear the buildings in the background, but I can deal with that. I know what days to show up and check it out and that's the important thing.

It also showed me (as I was playing around) a day in November when the sun should rise directly between the two, so I may be out there again then. I'm excited.

Thank you again! I can't believe that's a free program. I'm headed back to the creator's page now to see if there's a donate button, or maybe I'll just buy the iPhone app.
posted by komara at 7:58 AM on July 21, 2010

re: full moon rising

The full Moon and the Sun will always be on opposite sides of the sky. That's because for it to be a full Moon we have to be between the Sun and the Moon. But the location of the rising Moon and Sun will change over the course of the year.
posted by Phantomx at 11:35 AM on July 21, 2010

Am I missing some other fundamental idea, like "the full moon always rises over the same spot on the horizon" or something else?

Something else. Assuming you're in the northern hemisphere (as New Orleans is), the full moon rises and sets at points further north along the horizon in winter (and is higher in the sky at its zenith) during the winter, and further south along the horizon (and lower in the sky at its zenith) during the summer.

A quarter moon (a potentially misleading term, as this is when the moon appears half-lit; so named because it occurs at the 1/4 and 3/4 points in the moon's cycle of phases) rises and sets roughly due east and due west, respectively. The first quarter moon (about a week before the full moon) rises about noon and sets about midnight; the reverse is true for the last quarter moon (about a week after the full moon).

A crescent moon can generally only be seen just after sunset (for the "waxing crescent," just after the new moon) or just before sunrise (for the "waning crescent," just before), because it appears fairly close to the sun, and if the sun is above the horizon then the moon is lost in the sun's glare. It rises or sets roughly the same place the sun does, i.e., further north in the summer and further south in the winter in the northern hemisphere.
posted by DevilsAdvocate at 12:21 PM on July 22, 2010

Response by poster: I know you all are dying to know that tonight was one of the nights that was a good lineup. Unfortunately there are incredible huge slow-moving (unmoving, really) clouds sitting right between downtown and the moon. I stood in the still sticky nasty New Orleans summer air for 30 minutes hoping that at least the moon would rise above the clouds and make a nice picture, but by then it was too late.

30 minutes and the hike up the overpass in 90º weather (95º with the heat index) and 78% humidity makes komara a sweaty nasty man. Time to hit the showers. Good try, team - we'll get 'em next month.
posted by komara at 7:42 PM on July 26, 2010 [1 favorite]

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