I never thought I will be doing this but after I finished the implementation the viewfinder feature in the Planit app, it occurred to me. Why not try to date the famous Moon and Half Dome photo using this app?

Here is the original photo by Ansel Adams.


Let’s list the clues we had so far.

  1. Waxing Gibbous moon as we can see.
  2. There was snow on the ground which means it was in winter.
  3. We also know the photo were taken in 1960 and were taken after 3pm in the afternoon as Ansel said it in his Autobioyaphy. But he never mentioned the exact date and the exact time.
  4. The camera location is hard to be exact so we have to try our luck here.  The shadow on the left is the Washington Column. With that in mind, I put the camera at the below location so that the Washington Column is between the camera and the Half Dome.

After studying the map and the picture carefully, see below for where i place the camera icon and the scene icon. You can see the GPS coordinates of both locations below. I verified the camera location is at an open area to the west of the Ahwahnee Hotel so it is possible to get there and have a clear view to the half dome as I’ve been there before. On the screenshot below, the line between the two icons is green which also means there is nothing in between.

device-2014-04-19-224416 device-2014-04-19-222114

Now switch to Finder page, select Waxing Gibbous, select the date to be 1/1/1960 to 12/31/1960.  Now switch to the viewfinder view. The main advantage of Viewfinder view is you can drag the area on the viewfinder to define where to search. The area you drag will be concerted to the elevation angle (or altitude) and the azimuth. The altitude is fixed but the azimuth is a range. You can also drag the corresponding icon on the side to fine tune the values. The contour of the Half Dome really helps to determine the Moon location.

With just a few drags and clicks, I got the following three dates back. As you can see, only the last one meets all the conditions (winter, after 3pm).


Believe it or not, we just dated the famous photo. It was taken on December 28, 1960 around 4pm. The Moon is an 86.1% Waxing Gibbous. It would take hours of calculations but with this app, it is just a few minutes.

Since now I knew the moon position on the original photo, it is really easy for this app find all the date/time that match closely to the original photo. I just need to change the date range!

I googled a little bit and found in 11/28/2009, they predicted the Moon at the almost exact same location. They called it Moon and Half Dome Celestial Encore. You can find a link below.



Here is what this app shows on 11/28/2009. Unfortunately, no photo came out from that encore because there was cloud.

Of course, everyone would be more interested in when the next time would be in the future. So I set the starting date as today and the ending date to be five years later. Here is what I got for the next five years.


The best matching one is 12/29/2017. Sun and Moon position, time of the day are almost exactly the same as Ansel Adams’s Moon and Half Dome. If you would like to replicate the classic, that’s the time you should be at Yosemite.

Here is a quick comparison of 1960, 2009 and 2017. As you can see, the 2017 one is actually more accurate than the 2009 one in all aspects.

Date Time Moon Percentage Moon Azimuth Moon Altitude
(Original Photo)
16:05 86.1% 89.0 21.8
(Celestial Encore)
15:54 88.7% 88.7 21.8
16:06 86.3% 88.8 21.8