Evan Hazard / Northland Stargazing: Planets and smudges that aren’t comets
Our Abendstern, Venus, rides low in the west at dusk all month. It has come out from behind Sol, and is catching up with us, because we move more slowly in our orbit than do the inner planets. Venus is, however, moving rapidly against background stars. Once the sky is dark, find the constellation Leo above the WNW horizon. The blue-white star Regulus, at the bottom of the "sickle" at the west end of Leo is far from Venus on the Fourth of July, but will be only 1.25 degrees from Venus on July 21-22. That rapid approach results, of course, from the motions of Earth and Venus in their orbits. There is a good discussion of Leo at http ://en. wikipedia.org/wiki/Leo_(constellation).
The only other evening planet is Saturn, well up in the SW. Remember your Deet; mosquitoes may be bad.
Mars is a pre-dawn planet, low in the ENE above and left of thin crescent Luna on July 5. Jupiter is even closer to the horizon, below and to their left. On July 22, Mars and brighter Jupiter are only ¾-degree apart 45 minutes before sunup. Mercury has a decent morning apparition in late July, reaching greatest elongation July 30, below and left of Mars and Jupiter.
You still run into people who think summers are hot because we are closer to Sol. On July 5, Earth will be at aphelion, its greatest distance from Sol this year, 94,509,959 miles.
Almost exactly overhead during July evenings is the four-star "keystone" in Hercules. Between its two western stars is a smudge, visible with binoculars. This is Messier 13, the globular cluster in Hercules. Messier, you will remember, was a comet hunter, and made a list of more than 100 smudges that resembled distant comets when they are still far from Sol, so comet hunters would not be fooled by them. Initially called "nebulae" (clouds), they turned out to be a diverse group of objects of great interest.
Some are actual immense clouds of gas and dust lit up by nearby stars, other are loose groups (open clusters) of stars, probably all having condensed out of an original gas and dust cloud at the same time, others are distant galaxies like our own Milky Way. And some are globular clusters, relatively closely packed spheres of old stars. More than 150 revolve many light-years out around the central bulge of the Milky Way, and most other galaxies apparently also have them. See also: http ://en. wikipedia.org/ wiki/Globular_cluster.
We will revisit constellations next time.
Evan Hazard also writes "Threescore and Ten" for The Pioneer’s "Prime Time."