>I just bought my D5200 and tried to take some star trail >pictures with it and I get the error saying "subject is >too dark". Is there a way to bypass this feature?
Congratulations on your new D5200. Yes! You will have to use Manual exposure mode and Manual ISO. For shooting Star Trails you will more than likely have to use Manual Focus as well. Setting the focus distance to infinity.
>How do you guys take pictures like this?
There are two ways to go about shooting star trails. For both you will need a stable tripod and a remote shutter release like the Nikon MC-DC2. You should find a location with as little light pollution as possible under a new moon (black sky). 1. Shooting a single very long exposure possibly as long as 80 min. Set the aperture wide open at small f/# (f/2.8 or f/4). Set the ISO to the base setting (ISO 100) Set the shutter speed to Bulb. You will then have to experiment to find the most appropriate shutter speed for the conditions and scene you are shooting.
2. Shoot multiple images and combine them via Image Stacking in PP. Again set the aperture wide open (f/2.8 or f/4). Use a shutter speed beteen 30 sec. to 1 min. Adjust the ISO as required for a correct exposure. Then download the images to your computer and combine them using photo editing software.
Keep in mind that it takes practice and quite a bit of trial and error to get it right. Also the cameras meter is almost useless for shooting star trails.