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September 26, 2013 — A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis, Idaho Observatory; and Daryl Macomb, Boise State University.
In the autumn night skies, Pegasus, the winged horse, is a prominent constellation overlooking the October harvest. Named after the Greek mythological figure, Pegasus sprang from the neck of the Medusa, when she was beheaded by Perseus. Pegasus is noted by a great square, outlined by its three brightest stars -- Markab, Scheat and Algenib -- and Alpheratz, the brightest star in Andromeda.Although Pegasus seems to be devoid of any interesting naked-eye objects, it does have a few very interesting deep sky objects -- most notably, the classic globular cluster M 15; Stephan’s Quintet, a region of five closely grouped galaxies that are in the process of evolving; and Einstein’s Cross, which consists of four separate images of the same quasar that have been formed by the gravitational lensing of a nearby galaxy.
Planet and meteor alert: Saturn, Mercury and Venus can be seen right after sunset on the western horizon. Jupiter rises around midnight and Mars around 4 a.m. The Draconid meteor shower peaks around Oct. 7-8 and the Orionids around Oct. 21-22. Both are best seen after midnight.
October 2013 Interest: Venus' Surface
Last month, we discussed the atmosphere of Venus -- Earth's "sister planet" -- and it turned out not to be sister-like at all. Venus has very high pressures and temperatures compared to Earth, and its surface attributes are similarly foreign.
Of the many orbiter and lander spacecraft sent to Venus, the most productive was the Magellan spacecraft (1989-1994), which mapped the planet’s entire surface from orbit, using radar to penetrate the dense Venusian cloud layer. The URL above includes a movie of the radar-mapped surface with Venus rotating. The radar map resolves features down to a scale of about one kilometer.
The map shows that Venus is about 80 percent covered by smooth volcanic plains, with the remainder being two raised areas, or "continents,” one each in the planet’s northern and southern hemispheres. The continents are named Ishtar Terra (about the size of Australia) after the Babylonian goddess of love; and Aphrodite Terra (the size of South America) after the Greek goddess of love.
Venus has several smaller types of features, unlike any found on other planets in our solar system. These include dome or pancake-shaped areas ranging 20-50 kilometers in diameter, suggestive of ancient welling up of lava; ray-like fractures called "novae"; more complex radial and concentric networks resembling spider webs; and some lava channels more than 6,000 kilometers long.
Venus has few impact craters, most likely because its surface is relatively young. Its surface is less than 800 million years old -- more recent than the late heavy bombardment phase (roughly 4 billion years ago) hypothesized to have last cratered the Earth's moon and the other terrestrial planets of the solar system.
The Venusian surface is still much older than the Earth's average surface age of 100 million years, because Venus does not have plate tectonic dynamics that would continually refigure the surface. While mostly quiescent, Venus has 167 volcanoes larger than 100 kilometers in diameter, some of which may have been active in the recent past, as evidenced by sulfur in the atmosphere.
To view this month’s sky chart, click here.