Two of my favorite hobbies are photography and astronomy, and it only gets better when the two are combined.  I've had a few people ask for a tutorial on how I do my star trail and time lapse, so here it is.

Star trail images show the motion of the stars over a long period of time, making beautiful arcs.  Back in the film ages the method for making these images was to open the shutter and let it go for hours, but that method doesn't work too well with digital cameras.  When the shutter is left open for a long time on digital cameras all kinds of thermal noise, exposure issues, etc. can arise.  The best method with digital is the take a series of short (~20-30 seconds) exposures then stack them in specialized software to make the arcs. 

This method is also the general idea behind the creation of astro time lapses.  Instead of stacking the images one atop each other, as seen in the making of star trails, the images are displayed one after another to make a movie of the stars moving.  Below is an example:

My preferred software for making star trails and time lapses is the free Startrails application - http://www.startrails.de/html/software.html.  I find this program to be the most user friendly and easiest way of making high quality star trails / time lapses.  It will be this application that I will use in this tutorial.

Most of the techniques apply to both projects (setup, composition, technical details), and I will cover those first.  After those I will address some of the nuances to be aware of for each project.

Step 1: Materials

There are just a few things you need to get started with shooting star trails and time lapse, most of which you probably have sitting around at home:

A DSLR Camera
A Stable Tripod
for your camera to sit on.  It needs to be able to keep the camera perfectly still for long periods of time.
A cable intervalometer - used to set the exposure length and interval of the images.  This is probably the one thing you don't have, but they can be found cheap on the web.  Not necessarily needed if your camera has one built in, but I still prefer to have a remote.
A computer - used to process the images. 
A program to stack the images - I like to use the Startrails application for making the images.  http://www.startrails.de/html/software.html  This can also be done in Photoshop, but in my opinion, Startrails is easier.
A program to make the time lapse - There are numerous, but Startrails does time lapse as well, so it is my one-stop-shop to make star trails and time lapse

The setup for this is fairly simple - All you have to do is attach (or setup the in-camera) intervalometer, setup the tripod and camera, then point it at the part of the sky you want to shoot.

You may ask "What part of the sky do I want to shoot?", well the next step is for you.
<p>Awesome post, thank you! but I have a huge question. If the star trail is a complete circle does that mean you need to do it within 24h? if so how do you take the pictures when the sun is shining?</p>
Too bad the software is only for a PC. Do you know of any comparable Mac programs?
<p>I know this is a 1+ year question, but there is a software that I used a while back called StarStaX, which is maintained by a single dude and is free. It works on Windows, Linux and Mac.</p>
<p>Not to sure that this will help GeekFilter, but I've been looking at Hugin to do stuff like this. It should at least auto-align the images and has an option to output the physically transformed images separately, rather than merge them together. After that, it should be easy to use a photo-manipulation program like Photoshop or Gimp as jmandell42 suggested. Just wish one of these tutorials would give access to their raw images so I could try it out myself.</p>
The only other software I've seen used is Photoshop by placing all the images as separate layers then using the Lighten Blend Mode. Any software that can overlay one image on top another should work though.
<p>awesome, Thank you!</p>
<p>great pictures. is there a free version of this software or something similar for mac?</p>
Took my first picture using this technique last night, the battery on my camera died after about an hour and ten minutes but I'm still very happy with the result.
Very nice shot, especially for your first shot!<br> <br> One small critique/suggestion is to use a flashlight to illuminate the foreground in a shot or two. When you stack them the lit up trees will appear in the final image, making it look cooler :)<br> <br> That's one thing I should mention, make sure you have new batteries (or use an external power source). Photography like this can suck the life out of batteries very quickly, especially in winter.
Outstanding instructable. Thank you for posting. <br> <br>One quick question: how do you get the effect here? http://vimeo.com/54741100 It seems to be a combination of the stacking and time lapse but I haven't been able to figure out how to do it. <br> <br>Thanks!
Thanks for reminding me of that! I had seen something like that a while ago and forgot. Looking around in Startrails under the build star-trails mode there is an option available when Lighten is selected down at the bottom of the box that says 'save each image', and that will save an image each time another image is added, and then you make those into a movie to make the trails move. I'm just figured this out so I'll add another step in the main Instructable with a better explanation. <br> <br>Hopes this helps! <br>
Great! =D
Cool, nice affect.
Incredibly good pictures and a very good tutorial for someone who doesn't do a lot of digital stellar photography.
I've always done it the old fashioned way... leave the shutter open for an hour. With the software I think I will try my next one this way! Thanks!
Neat! Always wondered if I could do these. All I need now is an interalometer ^_^
You don't need to spend the $100 on the brand name one, we got one from china for $20 on eBay and we've used it problem free for aver a year now.
This is really cool! imIf I only had such a cam...
Ok thank you and this really helps good work
What do you recommend for the amount of shots
It really just depends your goal for the image and the time you have to shoot. If you want short trails or a shorter video clip then about 50-100 images will suffice. If you want really long trails then &gt;150 images is the way to go. Normally I'll shoot about 180-200 images of 30 second exposure or up to 300-400 with shorter exposures.
Very neat process. Makes beautiful pictures. Thanks for posting.
That's very useful, thanks! It should be interesting see the movie too :-)
yep, link already existing in first step! good done!

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