Did you have fun seeing double?

Did you have fun with double star Nu Draconis last week? Nu Draconis is the star on the upper left corner of the lopsided head of Draco, the Dragon. Look northeast after the sky is good and dark (9:30-10:00 pm MDT) for Vega, the brightest star are the area. The head of Draco is just to the left.

It may be a little difficult to separate them in binoculars, but even a small telescope works great.

Double stars are some of the most prolific in the sky. It is said that possibly up to 80 percent of the stars in the sky are doubles or multiple-star systems.

A double star is a pair of stars that appear close to each other when viewed from Earth. That being said, we must add that there are two possibilities for double stars. First, the stars are actual doubles, or second, they are an optical double.

First, an actual double. They are two stars that are actual double stars. They are bound together by gravity and orbit each other. Whereas, optical doubles only look like they are close when in fact they can be far -- often many light-years -- apart.

They are referred to as being along the same line of sight and it only makes them look like a double star.

Probably the most famous double star pair in the sky is the Mizar/Alcor pair located at the crook in the handle of the Big Dipper.

This pair has been in recorded star observations for thousands of years and was said to be an ancient test of eyesight for soldiers. The pair is easily seen without an optical aid but binoculars improve the view.

When telescopes began to examine the heavens it was discovered that Mizar itself is a true double with a small companion but the Mizar/Alcor pair are an optical double with Mizar being 78-light years away and Alcor at a distance of 81 light years.

It was also discovered that the Mizar/Alcor system is really composed of a total of six stars.

We will look at a few more double stars next week--including two of my favorites. If you would like to know more about double stars, or have an interest in them, the Astroleague has a double star observation program for beginners and more advanced observers.

Information can be found at www.astroleague.org, click of the "observe" link then scroll down to "programs." On the list provided look for "Double star observing.

SKY WATCH: New moon, Monday, July 4. Remember, new moon means no moon visible. July 4, is also the day Earth is farthest from the Sun in its annual orbit. If we are farthest, why is it so hot? Blame that pesky 23.5-degree axial tilt. It is good to have our old friends the Summer Triangle of Vega, Altair, and Deneb back in our early evening sky. Jupiter is still visible in the southwest and the Mars/Saturn pair high in the south playing tag in Scorpius and Libra. Good to have Scorpius back too, that means all those lovely nebulae and star clusters there and in Sagittarius are nearby.

NEXT WEEK: A few more double stars, and more astronomical blathering.