Starlight photography requires long exposures. Example shows affect of moving stars, earth's rotation blurring the stars as oblong dots. Besides earth rotation the smallest amount of equipment movement or vibration can ruin a shot. A stable camera on a solid tripod is required. It may take more than a solid tripod to control blur. Blurry picture has a list of possible causes. Cause in bold, explanation with possible soutions follow.
Camera out of focus
Entry level cameras are notorious for being unable to focus in the dark. Setup your tripod and camera when the sun is still out. Focus on the trees while there is still enough light to see. If the sun has already set I imagine you could shine light up the trees, doing so may allow a camera to focus properly. Car lights certainly will help but its not a good idea. Bright lights in the dark will blow your night vision.
The photos in this essay cannot be taken without a tripod, period. If you are new tripods, they all look the same on the internet, many boast the similar features. Know one thing: lightweight and easy to carry are not desireable features and benefits. At the end of the day invest a couple a hundred dollars on a quality tripod. Get one from a brick and mortar camera dealer. Learn what is right for you in person and buy it in a store.
Tripod not stable
Bump the tripod and the shot is ruined. Gust of wind the shot is ruined. Dog entangles leash on tripod, knocks over equipment onto ground, lens is ruined. Of course antsy dogs are not helpful around tripods in the dark. Either way its no good to use an unsecured, unstable tripod. May be helpful to put small sandbags on the legs. Nothing real heavy just a few pounds of weight on each leg.
Camera not secured to tripod
Just screwing down the camera to the tripod may not be enough. Over time most tripods with will wear at the mount, become loose where the camera secures onto the tripod. Some are so loose they become sloppy and useless. The smallest amount of play really exaggerates as blurry photos when doing long exposures. Make sure the camera is secured tight. It may be you need to put a thin piece of foam or rubber between the camera and the tripod to make it extra secure. Yes its kind of a half assed solution for sure. But that's the fun of working with entry level gear, older equipment and used equipment.
Tripods come in all different possible configurations. A portable device with three legs which collapses and expands. Imagine anything like that has many moving parts. Moving parts wear over time and become loose. My tripod is expensive, heavy and good quality. But after 27 years of use and abuse its sloppy in some of the moving areas. Figure out what is moving and make it sure its all rock solid stable.
Camera moved when triggered
Your fingertip motion depressing the shot vibrates the camera. Holding down the button with a shakey hand can vibrate the camera. Solution is to get a remote cable. Every camera is different, in the old days it was called a blub release. You may find it called a remote button. Every manufacturer has a differnet term for it. I found Opteka makes good aftermarket ones for Nikon. Better still get a gizmo called an Intervalometer.
By ground I mean where ever your tripod is located. I took a series of really blurry night photos and could not figure out what went wrong. Exposure was near perfect but every shot was blurry. I was in a remote cabin in the middle of nowhere. Amazing stars all around during a crystal clear night. I was taking the photos with my tripod placed on the deck attached to the cabin. Every time I stepped near the camera the deck boards vibrated just enough to throw off the picture. Even my dog walking on a deck vibrated the deck boards, ruining the shots. Very small deck board motion travelled up the tripod legs and vibrated the camera. May as well been a trampoline frequented by kangaroos.
Camera's internal vibration
Inside SLR cameras are a moving parts. A large moving part is the mirror. Trigger the camera, up flips the mirror, camera vibrates ever so slightly. Depending upon the camera there is a way to work around the moving mirror. Each camera is different, its a feature called mirror lock up on Nikon. Not sure what its called on other camera brands.
The moon moved in the sky
Sounds obvious but the moon moves in the sky during the course of the night. Keep in mind the path of the moon may adversely affect the composition of a very long exposure. The moon is a big white blurry streak when it travels through your image.
The stars moved in the sky
Star trails, good when you want artsy star trails, bad when you don't. I've read a good rule of thumb from a real deal aurara film photographer Dick Hutchinson. He's a person with real experience in up in Alaska. Great advise on taking Aurora pictures on his journal. I gleaned a rule of thumb from his journal.
I have done no tests for myself but plan to do so. Dick Hutchinson's rule of thumb rings true to me: 600 divided by the focal length of the lens. Imagine 600 divided by an 18mm = any exposure longer than 33 seconds stars begin to have trails. Makes sense to me, the longer the exposure the more likely the stars moving in the sky will begin to have a curved trail. All curves center on the north star which doe not move.
Above are the causes and adverse conditions of what can go wrong. I'll dive into specific photos and what I beleive went specifically wrong. Lets investigate in the next troubleshooting essay.