An Artificial Star is a point source of light. It is used to simulate a real star indoors, so you can collimate your telescope's optics indoors and/or during daylight.
Commercial artificial stars, such as this Hubble Optics one, cost $25 or more, and their main feature is a small plate that has precision holes of 50 micron up to 250 microns.
You can make your own artificial star, which is very close in function to the commercial ones.
You can watch this short 4 minute video on how I did it, and read on for detailed instructions.
Why Use An Artificial Star
Collimation is aligning the optical components of your telescope, so that they all have a common axis. Without proper collimation, the shapes of stars can be distorted. Collimation specifics depend on your telescope optical design. For example a Newtonian telescope usually has 3 adjustment screws on the back of the primary mirror, an SCT has 3 screws on the secondary mirror (on the front), and so on.
Although you do the collimation using real stars, there are several disadvantages:
- First, your telescope must be tracking the motion of the sky.
- Second, it can be difficult in the dark to see and manipulate the screws that you need to adjust.
- Third, in the dark you can inadvertently touch the front corrector plate of your SCT, or worse, scratch or break it using the screw driver that you use for adjustment.
- Finally, you are wasting valuable observation time fiddling with collimation.
If you can collimate indoors, then you avoid all that.
You need the following:
- A small flashlight, the kind that costs $2 at the Dollar Store.
- A piece of kitchen aluminum foil that would fit on the front of the flashlight.
- A fine sewing needle.
- A rubber band.
Use the finest sewing needle that you can find. Check your wife's or you mother's collection (at least that is what I did).
Draw a circle on the foil using a Sharpie marker to match the front of the flashlight. Then mark 4 or 5 points near the circumference of the circle that you drew.
Lay the aluminum foil flat on a hard surface, but not too hard. I used a glossy magazine. Press the needle very gently on one of the dots. Then, with slightly increasing pressure, do the same for the other dots, so the holes are larger (and the stars brighter).
Fold the piece of foil on the front of the flashlight and secure it with a rubber band.
That is all you need.
How To Collimate Using An Artificial Star
Now, place the artificial star as far away from the telescope as you can. Focus your telescope on the stars, then defocus both sides of the focus (in focus and out focus) to check the collimation. Adjust the optics using your collimation screws.
I used a DSLR camera with a zoom feature, because that is what I use for astrophotography. Also, I can swivel the LCD screen so I can adjust the screws on the front of my Celestron C8 SCT while watching.
Although convenient, a camera is not strictly needed. You can use your high power eyepiece (3 to 5 mm) instead.