Using a Telrad
By Shawn Grant
The Telrad is one of the best accessories you can have for a telescope. In fact, it is a must have. The Telrad is a zero power pointing device that displays a three ring target onto the starry sky. Everything is right side up and you see the sky exactly the way you see it with the naked eye. Let’s find out how to find elusive targets with the telrad.
Remember that last month you made overlays of the Telrad for your charts. You will learn how to use these overlays effectively. One of the best objects in the summer sky is the great cluster M13. On your chart find Hercules and place the center of the telrad overlay right on the symbol representing M13. The "keystone asterism" makes the main body of the strong man Hercules. M13 lies on the western side of the keystone between the two stars eta Hercules and zeta Hercules. Draw a straight line between those two stars. You will see on your chart that the top of the outer Telrad ring is just a degree south of eta Hercules. With your telescope position it where the Telrad target is position against the star background exactly that way the overlay is on your chart. Look in the eyepiece and you will see the great cluster M13. That seems a little complicated but if you have a good knowledge of the constellation patterns and the sky is a familiar place it is second nature.
Let’s try another example. M57 the Ring Nebula is fairly easy. We will find this then move onto something more challenging. M57 is in the constellation Lyra. Part of Lyra makes a rectangle. When finding deep sky objects learn to make shapes like triangles squares and so forth. This will help greatly in the success of finding an object. M57 is on the southern side of the rectangle between the stars gamma and beta Lyra. Place your Telrad on M57. You will notice that the 2 degree circle touches both gamma and beta . Use this to your advantage. Aim your telescope to where your Telrad matches your overlay and chart. In the eyepiece you will see M57.
M13 and M57 are very easy objects to find but how do you find challenging objects with a Telrad. Let’s explore this further. M12 is a nice globular cluster to look at. But not very many people look at it because one Ophiuchus is a hard constellation to pick out and two there aren’t very many bright stars near by. Learning the naked eye sky is a must for success of finding objects. First learn to pick out the shape of Ophiuchus. Ophiuchus covers a lot of area and there are many interesting objects to look at. The best way to find M12 is to pick out the nearest fairly bright star. In this case it would be lambda Ophiuchus. Look 4 degrees to the east and you will see a group of 4 5th to 6th magnitude stars. Sense we do much of our observing at dark location these stars are still bright enough to be easily seen. The top of the Telrad outer 4-degree circle should be positioned half a degree south of the group of stars. M12 should be in the eyepiece. Here is another way to find M12. Remember you can use the Telrad’s circles to measure distance. Let’s use that fact to our advantage. M12 is 5.5 degrees from l Ophiuchus. So what to do. Position the Telrad where the outer circle touches lambda Ophiuchus. Now from the one end to the other is four degrees. Move the telrad southeast to where the small circle is centered where the eastern side of where the large circle was. We just got have 1.5 degrees to go. Use the mid sized circle to figure 1.5 degrees and move accordingly. M12 should be very close to the eyepiece.
You probably won’t master these techniques right off. Give yourself time and practice. In time the telrad will be second nature to you.
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