Have you ever wondered how some photographs are made? For example, below is a composite image taken during a Geminid Meteor Shower. All images were taken from the exact same location, but there were only a few meteors that night. In order to show all the meteors I saw in one image, a composite image has to be made. I essentially took the meteors from the other photos and copied them into this image using Photoshop.
Astrophotography images are more often than not composite images - that is, multiple images of different exposures/scenes merged to make one single image. This is often necessary when shooting the night sky since the proper exposure for the sky (generally 10 to 30 seconds long) will typically leave the foreground completely black, especially if the moon is not out. Exposures for foreground images are often on the order of minutes, sometimes as much as 20 or more minutes.
If you really wanted to take an astrophotography image in one exposure when the moon is not out, you could "paint" the foreground with a flashlight, such as the image below. This was a single exposure and the foreground was lit with three flashlights - three of us were running around like crazy trying to evenly paint the foreground with the flashlights within the 15 second exposure window that was set for the sky.
As you can see the foreground was not perfectly evenly lit in this shot, so in order to get it looking the way I intended I made a composite out of a couple of images in Photoshop. The next image is the final result, overlaid with the above shot, which was a single exposure.
Trying to get the foreground evenly lit in this shot with three different people running around several hundred yards apart was not easy. We attempted this about 40 times before we were satisfied - and we were running out of breath after about the 5th attempt! Below are a couple of examples of the many failed attempts. As you can see, making a composite image when it comes to astrophotography is generally the way to go. It isn't the easiest skill to learn, but it is well worth the effort.
Here are a couple more examples of composite images I have taken. This first one compares what the shot looked like straight out of the camera with the foreground not lit by any artificial light source to the final composite image in which the foreground was lit with a single flashlight.
Below is another composite image, and one of the first ones I ever made (maybe my first ever?). I didn't have the greatest equipment back then and had next to no knowledge of astrophotography, so the image has a lot of issues, but you can see that even with these road blocks, I was still able to come away with a half decent image. The sky was a 25 second exposure and was taken prior to the foreground image. The foreground image used in the composite (not shown) was about a 6 minute exposure as there was no moon out to illuminate any of the foreground. Also, no flashlights were used in the foreground image, which had I have known better would have made the foreground image infinitely better. But that's how you learn!
Making composite astrophotography images takes lots of practice and even more patience! In the end it is a skill worth having if you want to get killer astrophotography shots! If you have any questions at all, just shoot me a message or leave a comment. Thanks for reading!