Western Slope Skies - August Skies

Aug 12, 2016

Credit Public Domain (CC0)

A clear evening in late August offers much to contemplate, both near, relatively speaking astronomically, and far.

Looking roughly south after sunset, the planet Mars is first to appear as the sky darkens.  On the night of the 24th, Mars passes less than two degrees, the width of two pinkies held at arm’s length, from the star Antares, and the two objects, along with Saturn to the north, form a six-degree straight line.  Similar in color, Mars is about three times brighter than Antares.  The proximity to Antares of both Mars and Saturn enables us, over the coming weeks, to discern the movement of the planets relative to the fixed background of the stars.  Ancient civilizations observed this motion, which led to the term “planets,” a translation of the Greek word for wandering star.  Being closer, Mars orbits the Sun much faster than Saturn.  Mars’ changing position relative to Antares will be apparent sooner.

Antares, named because of its distinct red color, is Greek for “Rival of Mars.”  Other, and more ancient, civilizations knew the star as the heart of the Scorpion.  Antares is a red supergiant star with a surface temperature much cooler than our Sun. If Antares was located where our Sun is, its surface would reach beyond the orbit of Mars.  At a distance of 550 light years, it is one of only a handful of very bright stars near enough in the sky to the ecliptic, the path of the Sun and planets through the Zodiac, capable of being occulted by the Moon.

Two other planets approach each other this month.  On the evening of the 27th, Jupiter and Venus will be extremely close, very low near the western horizon at sunset.  Lower still will be Mercury, shining much more feebly than Venus and Jupiter.  All three will be more easily seen with binoculars, but a clear, low horizon will be necessary. Wait until the Sun has actually set to scan the sky safely without the possibility of inadvertently coming upon the Sun.

Western Slope Skies is produced by the Black Canyon Astronomical Society.  This episode was written by Bernie Forman and recorded by Art Trevena