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The Sky This Week, 2016 July 19 - 26

Look up. Yes, we've been there.
Apollo 11 Landing Site, 2013 September 24
with craters named for the astronauts

The Moon wanes in the late evening and early morning sky this week, climbing through the dim constellations of the autumn sky. Last Quarter occurs on the 26th at 7:00 pm Eastern Daylight Time. Luna’s nightly progress is a bit hard to measure as she passes no objects that are brighter than third magnitude.

If you look at the Moon early in the week, consider that 47 years ago the first explorers from planet Earth left the first footprints on her dusty surface on the evening of July 20. For most of the people who currently inhabit the planet this is an event that is written about in history books, but there are still many of us who remember where they were and what they were doing at this momentous time. I was an avowed "space geek" who spent most of the day explaining to my parents and their friends exactly what was going on with my scale models of the Apollo spacecraft and the Saturn V rocket. As evening settled over us I set up my 3.5-inch telescope on the patio and shuttled back and forth between the 19-inch black-and-white TV and the "live" view of the Moon in the telescope eyepiece. From that moment to the present day the Moon has somehow looked a little different to me whenever I’ve looked across the gulf of space to its foreboding surface. The Moon’s appearance hasn’t changed, but the though it always in the back of my mind that "we’ve been there". Today we are still embarked on a journey of discovery, but rather than human footprints on distant planetary surfaces, we have left tire tracks and assorted pieces of hardware in our wake. Look at the Moon and planets on any night over the next few weeks. In one way or another we’ve "been there", and for Venus, Mars, Jupiter, and Saturn we still are. Mars currently has two surface rovers and several orbiters returning information to us, the Juno probe has successfully entered orbit around Jupiter, and the Cassini probe has been orbiting Saturn for over a decade. Look through a telescope at Saturn’s brightest moon Titan; we’ve been there, too.

Venus is perhaps the planet that has attracted the most attention from space probes. It has been visited many times by flybys, orbiters, and landers, and today is being investigated by the Japanese Venus Climate orbiter. In many ways it is a very hard planet to explore thanks to both orbital mechanics and its incredibly hellish surface. It is far easier to send probes outward than it is to send them sunward, and once you’ve arrived at Venus the surface is perpetually shrouded in dense clouds. Thanks to a thick atmosphere of carbon dioxide landing on the planet’s surface requires a well-armored payload since the surface temperature is higher than the melting point of lead and the atmospheric pressure is 90 times that at the Earth’s surface! You can explore Venus from a somewhat easier perspective if you look just above the western horizon shortly after sunset. The planet will continue to linger in the twilight glow until later this fall, when it will move to a place of prominence in the evening sky.

Jupiter hangs in the west as evening twilight fades. By the time full darkness falls, though, he’s only 15 degrees above the horizon. You’ll have a short time to look for details on his cloud tops before distortion from our atmosphere smears his disc into a wriggling blob.

Mars is still worth a glimpse through the telescope as twilight fades to darkness. The planet’s southerly declination means that you’ll need steady air to spot details on his surface, but this week some of his more prominent features are turned our way. You’ll also notice the planet’s pronounced gibbous phase. To the naked eye he moves eastward toward the star Dschubba, middle star in the "head" of Scorpius.

Saturn follows Mars across the meridian, crossing from the eastern to the western side of the sky by around 9:30 pm. This is the best time to view the ringed planet as it is the time when he’s highest above the horizon. As with Mars you’re looking though lots of Earth’s atmosphere, but the rings are visible in all but the most turbulent conditions. Early in the week look for Titan well west of the planet.

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