Sky Watching — August 2011

A Perseid Meteor

 Image Credit

 

The player above is for the Abrams Planetarium Podcast for August 2011

August is Perseid Meteor Shower time.  Each year during the summer months (mid-July through late August), the earth crosses the track of Comet Swift-Tuttle.  The path is full of dusty debris that has been scattered along the comet’s orbit.  These fine particles are orbiting the sun and they hit our atmosphere.  The meteor events occur when the particles enter the atmosphere and they vaporize.  We see a quick flashes of light — meteors, shooting stars.   Perseid meteors can been seen anywhere in the sky, but they seem to emerge from the constellation Perseus and are named for that radiant point.  Perseids are best observed after midnight when the radiant constellation rises high in the northeastern sky.  On the peak morning, August 13 this year, about 60 meteors per hour are visible.  This year, the moon is full and in the sky when the shower peaks.  Only the brightest meteors are visible.  On August 11, the moon sets around 3:30 a.m. and at 4:30 a.m. on the next morning.  On these two mornings, a large number of Perseids can be seen before twilight begins.

 

In the photo above, the single Perseid meteor streaks across the field of view during a long time exposure as the stars appear as parallel arcs.

 

Moon Phases
New	8/28
First	8/6
Full	8/13
Last	8/21

 

Let’s start this month’s sky watching with an “extra for experts.”   Mercury is an elusive planet and usually very difficult to see.  It is best seen during either autumn mornings or spring evenings when the plane of the solar system makes a very favorable angle with the horizon.  Mercury is visible late in the month about 30-45 minutes before sunrise.  With binoculars and with a good view of the natural horizon, look for it low in the eastern sky.  A thin crescent moon is nearby about 30 minutes before sunrise on August 27.

Venus is not visible during August.  It is at superior conjunction on August 16; that is, it is behind the sun and lost in the bright sunlight of daytime.

Mars is a morning star in front of the stars of Gemini, starting to rise early enough to be seen in a dark sky in the east.  While visible throughout the month in the predawn eastern sky, it rises around 3:30 a.m. at mid-month, later earlier in the month.  On the morning of August 25, the moon is nearby as shown in the chart above.  Castor and Pollux, the Gemini Twins, are nearby throughout the month.

Jupiter shines brightly in the predawn sky throughout the month.  It easily outshines the other stars in that region of the sky.  On the morning of August 20, the moon appears near Jupiter and Hamal, the brightest star in Aries.

Saturn shines from the western sky throughout August.  The moon passes near Saturn early in the month as shown in the diagram above.  The bright star Spica is nearby.

In early August the moon passes in front of the stars of Scorpius during the early evening hours.  One bright star, Antares, makes a nice pairing with our lunar neighbor on the evening of August 7th.  The stars do not have vivid colors, although Antares shines in a ruddy color.  The star’s name is sometimes translated as the “Rival of Mars.”  Ares is the Greek version of the god of war (Mars).

Antares is quite unusual.  Its distance is measured at about 600 light years.  A star like our sun is not visible at that distance without the assistance of a telescope.  Antares is known as a red supergiant.  In the final stages of its life cycle, it shines at the brightness of 65,000 suns.  It is enormous with a volume that, if empty, would hold over 500 million stars the size of our sun.  Placed in our solar system, its volume would extend into the vicinity of Jupiter, some 480 million miles from the center of our solar system.

Video Credit

Antares lies to on the west side of the Milky Way, the greatest density of stars, that outlines the plane of the galaxy by the same name.  The Milky Way stretches high in the eastern sky and then  into the north.  As August evenings progress, the great mass of stars rises higher in the sky.  The faint Milky Way glow can be seen during times when the moon is dimmer, such as before First Quarter and after Last Quarter, and in the countryside that is free from the glow of bright streetlights.  The time-lapse video above shows the Milky Way rising.  In the movie look carefully for Antares as it rises and it is low in the sky to the west (right) of the Milky Way.  The movie is made in the spring when Antares and the Milky Way rise later in the night.

Take a look at the sky events and tell us what you are observing on the comments section of this posting.