Sunset tonight is 7:28. If you look toward the west at 8 as the twilight is darkening, you will find ever brilliant Venus nine degrees above the horizon.

Just above Venus is Mercury and just above Mercury are Castor (on the right) and Pollux (on the left) in Gemini the Twins.

Astronomical twilight ends by 9:08 p.m., a good time to look toward the east to see very bright Vega in Lyre the Lyre 60 degrees above the horizon.

Vega is the fifth-brightest star in the sky. Lyre is a very small but delightful constellation.

Once you have found Vega, look just to its right (south) and slightly toward the horizon to see a parallelogram formed by four fairly bright stars. That is the main portion of Lyre.

Higher above the eastern horizon from Lyre is Hercules the Hero. Hercules will be on his side. He is represented by a misshapen square of four stars which are his body with stars extending from his body as arms and legs. Hercules is not one of the brighter constellations but easily seen on a reasonably dark night.

Along the western side of the "square" portion of Hercules toward the northwest corner of the square is a faint density that is visible to the unaided eye in a dark sky.

Through a small telescope this density reveals itself to be a compact ball of thousands of stars, a globular cluster named M13, the 13th object described in a famous catalog of nonstellar objects complied by the French astronomer Charles Messier (1730-1817) in the 18th century. M13 is a favorite object of amateur astronomers both for viewing and photography. It is about 25,100 light-years away and contains several hundred thousand stars.

Moon Watch

The moon is a very thin waning (growing smaller) crescent going to new moon on Saturday.

Learn more

Friday's meeting of the Tucson Amateur Astronomy Association will start with an overview of the methods used to detect planets in orbit around stars beyond our sun.

Next, the meeting turns to the search for another Earth. Steward Observatory graduate Ben Rackham will present an overview of the observational techniques fueling this revolution, focusing on transmission spectroscopy, the study of transiting exoplanets at multiple wavelengths.

The free event starts at 6:30 p.m. in Room N210 of the Steward Observatory, 933 N. Cherry Ave., on the University of Arizona campus.

Contact Tim Hunter at