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Wyoming Skies for June

May 28, 2010

A monthly look at the night skies of Wyoming, written by Ron Canterna, professor in the University of Wyoming Department of Physics and Astronomy.

The June skies may appear empty compared to the winter and spring skies, but the summer skies are full of interesting objects.

An unobstructed view of the northern horizon presents the notable constellation Cassiopeia, now a stretched-out, giant "W" in the sky. Late in the evening on the eastern horizon Vega, then Deneb (more northerly) and Altair, which in combination make up the summer triangle, will rise. Going toward the southern horizon you will notice a curly cue-shaped constellation with a bright, red star, Antares. This is the constellation Scorpios which is directed very close to the center of the Milky Way galaxy.

In a dark site you can see the Milky Way running almost parallel to the southeast horizon through these constellations. For planet watchers, Venus is the evening star on the western horizon, with Mars in Leo and Saturn in Virgo -- all seen in the early evening. Look for a partial lunar eclipse June 26. The summer solstice falls on June 21.

June interest: The Lesser Lights of the Solar System, The Gegenschein and Zodiacal Light.

The solar system is filled with little dust millimeter-sized particles constantly replenished from the asteroids orbiting in the ecliptic, the orbiting plane of the planets. These dust particles are packed in a pancake-shaped cloud and reflect the sun's light.

Right after sunset and before sun rise, there is a diffuse glow in visible light that can only be seen in dark sites and on moonless skies. It is brightest near the sun and falls off dramatically giving it a triangular shape. This is the Zodiacall Light or Zody to astronomers.

Now directly opposite the sun is another phenomenon called the gegenschein ("counter glow") in German. This is due to the direct and efficient back-scattering of the sun's light by these tiny dust particles from the zodiacal cloud.

To see images of these two lesser lights of the solar system, go to NASA's astronomy picture of the day at and search for images. If you are in a dark site, away from city and small town lights, see if you can observe these lesser lights.

For more information, visit the Wyoming Skies home page ( or send an e-mail to

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