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Skywatching August 2012


Each August, our planet moves through a trail of comet debris. That debris results in the Perseid Meteor Shower. In this photo the streak of light on the left side of the image is a meteor.

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August signals the move into late summer.  First we experience a dramatic loss of sunlight, losing nearly an hour of the sun’s warmth during the month.  At night, the Milky Way arches across the sky from dark locations.  At mid-month our planet passes through comet fine debris.  The material collides with the air and glows temporarily — a meteor or shooting star.  The meteors are associated with Comet Swift-Tuttle.  The display of meteors through the night peaks on the morning of August 12, just before twilight begins.

Meteors can appear any where in the sky, but they seem to emerge from the constellation Perseus which rises in the northeast during early evening hours moving toward overhead during the night.  Because the meteors seem to emerge from the region of this constellation, the display is known as the Perseid Meteor Shower.

On the morning of August 12, the moon is in a waning crescent phase, rising in the southeast at 1:10 a.m.  Even with the moon in the sky, Perseids can be seen anywhere in the sky.  The typical rate is about one meteor per minute appearing anywhere in the sky.

Moon Phases

Full Moon — August 1 and August 31
Last Quarter — August 9
New Moon — August 17
First Quarter — August 24

Morning Sky

Venus and Jupiter continue to shine as bright Morning Stars during the month.  The chart above shows the planets on August 1 at 4 a.m. with Venus near Zeta Tauri and Jupiter near Aldebaran.  The planets are visible well into bright morning twilight.  For details about Venus as a Morning Star, see our posting detailing its appearance in the morning sky.

At mid-month, the moon moves through the sky where the Morning Stars appear.  The chart above shows the view at 4 a.m.

Mercury enters the morning sky and reaches its Greatest Elongation West on August 16.  Mercury always appears in the sky during bright twilight, making it difficult to see.   Because its orbit is inside Earth’s orbit, Mercury is never seen on the nighttime side of Earth.  We only see it before sunrise or after sunset, never at midnight.  The chart above shows Mercury on the morning of August 15 at 5:30 a.m.  The moon is nearby and Venus higher in the sky.  From a viewing spot with a good eastern horizon locate Venus and the moon.  Mercury is to the lower left of the moon.  Binoculars will help with the identification.

By month’s end Venus’ rapid orbital motion has a moved it away from Jupiter.  The chart above (click it to see it larger) shows Venus and Jupiter at 4:30 a.m. on August 3o.  The bright stars that appear in the early evening sky during early winter appear in the eastern sky during late summer’s predawn hours.  The Gemini Twins, Castor and Pollux, Betelgeuse and Aldebaran appear in this view.

Evening Sky

Mars and Saturn are visible low in the southwest during early evening hours.

On August 1, look in the southwest as the sky darkens. The chart above shows Saturn above Spica, the brightest star in Virgo,  with Mars nearby.

Mars moves rapidly eastward in its orbit during the month.  We will observing it moving toward Saturn and Spica.

By August 10, Mars approaches Saturn and Spica.

On the evenings of August 13 and August 14, Mars appears to pass between Saturn and Spica.  On the 13th it appears closest to Spica.  Mars is several million miles away and Spica is 260 light years distant.

On the evening of August 17, Mars moves closest to Saturn.  While the two planets appear close in the sky, they are over 750 million miles apart, about 8 times the distance between our planet and the sun.

Later in the month, the waxing crescent moon joins the group.  The chart above shows the grouping on August 21 at 8:45 p.m.  It is important to find a clear western horizon to see this view.

On August 24, a few nights after it passes Mars, Saturn, and Spica, the moon appears near Antares in the southern skies after sunset.  It is easy to confuse Antares with Mars.  Both are about the same brightness and color, and the moon appears near both.  Antares is the brightest star in Scorpius.  It is a unique star.  With a cool temperature, indicated by its ruddy color, Antares must be a very large star.  At a distance of about 600 light years, this star shines with a brightness of over 17,000 of our suns.  Antares must be over 500 times larger than the sun, meaning that if we replaced our sun with Antares, the star would fill the inner solar system and extend to nearly Jupiter!

The chart above (click it to see it larger) shows the position of the visible planets on August 15, 2012.  Mars and Saturn are on the same side of the solar system, appearing in Earth’s night sky.  Mercury, Venus, and Jupiter are on the morning side of Earth.

August 2012 provides several opportunities to see celestial events:  a meteor shower and planets in both the morning and evening skies.

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