Good question. The answer? It depends...
Here's are the simple rules-of-thumb:
- If the sun or moon are going to be in the frame, then the red pin should be the camera position
- If the sun or moon are out of the frame (i.e. illuminating your subject), then the red pin should be placed the subject position
Let's delve a little deeper into why that might be.
If you want to capture the full moon next to your subject, then what matters most is the relative position of subject and moon as seen from your shooting location. An example: Full Moon Setting beside Longs Peak from Twin Sisters. In this shot, the intent is to capture the full moon before it sets next to Longs Peak. The red pin is placed on the top of Twin Sisters from where the shot will be taken. Placing the red pin at the shooting location makes it easy to judge the azimuth and altitude of the moon relative to Longs Peak:
On the other hand, if you wanted to shoot the sun rising on Longs Peak, then what matters more is the time when the sun will hit the peak. The sun will be behind the camera, well out of the frame, but will be illuminating the peak:
In this case, the red pin is best positioned on the subject, Longs Peak, so that the time, azimuth and altitude are specific to the subject which will be illuminated. You don't care so much what the sunrise details are for Twin Sisters - what matters is the subject:
Note: of course, in this example, the differences between sunrise time/direction for Twin Sisters vs Longs Peak are minimal. However, if you were shooting telephoto over a much greater distance, e.g. Mt Rainier from the Seattle area, these differences do start to matter.
Also, in the case of a prominent summit, it's important to account for the height above the horizon. In the case of Longs Peak, the summit lies around 9,000'-10,000' feet above the plains to the east. When you enter the elevation at the horizon, you'll see that sunrise occurs around 10 minutes sooner than the standard time. The key lesson? Get there early!