August 2015 Sky Watching


Sun

daylight_1508

The days of August lose about 75 minutes of daylight, finishing with about 13 hours, 10 minutes of sunshine.  The red line on the chart above shows the length of daylight for each day during the year.  The shaded area shows the daylight for this month.

Moon

NASA Photo

NASA Photo

Phase Date/Time Moonrise Moonset
Last Quarter 08/06/15 (9:03 p.m.) Midnight 1:06 p.m.
New Moon 08/14/15 (9:53 p.m.) 6:02 a.m. 7:44 p.m.
First Quarter 08/22/15 (2:31 p.m.) 1:37 p.m. 11:57 p.m.
Full Moon 08/29/15 (1:35 p.m.) 7:25 p.m. 7:13 a.m.
Times are Central Daylight Time for Chicago, Illinois, from US Naval Observatory calculations. (For mjb)

Perseid Meteor Shower

A Perseid meteor streaks across the sky during the Perseid meteor shower on Tuesday, Aug. 11, 2009 in Vinton, Calif. (AP Photo/Kevin Clifford)

A Perseid meteor streaks across the sky during the Perseid meteor shower on Tuesday, Aug. 11, 2009 in Vinton, Calif. (AP Photo/Kevin Clifford)

August brings the annual Perseid meteor shower.  The meteors originate from Comet Swift Tuttle (109P).  Comets are composed of ices and dust.  Comets move from the solar system’s colder zones and swing around the sun in elongated orbits.  During the time they are near the sun, the ices evaporate and the dust is scattered in wide swaths along the comet’s pathway. For the Perseids, the cometary dust cross our planet’s orbital zone.  During mid-August each year, our planet crosses that debris and the small dust grains enter the atmosphere, vaporize, and cause the air around them to glow — a shooting star or meteor.  The meteors seem to originate from the constellation Perseus, indicating the name of the shower.  The Perseids join 10 other annual showers that are from cometary debris.

Perseus rises in the northeastern sky at sunset.  During the night it rises higher in the sky, reaching its highest point just after sunrise.  Perseids can be seen anywhere in the sky, but they seem to emanate from Perseus.  Sporadic meteors also appear at the time of the shower, but their flight is from random directions.

At its best during the early morning of August 13, as many as 90 meteors each hour can be seen.   With the moon nearly new, the sky is free from distracting moonshine.  The predicted visible rate is diminished by street lights other outdoor lights.  The visible rate is further reduced by the reality that a single person cannot observe the entire sky all the time.  For any single person, the rate is likely 15-20 meteors per hour.  Perseids are best observed with four people, each looking in different directions in a very dark location.

Saturn

sat_lune_150822

During early evening hours, Saturn appears in the southern sky near the star Antares.  The moon appears near Saturn on the evening of August 22.

Mars

mars_lune_150812

Mars enters the morning sky, appearing low in the northeastern sky.  The moon helps with its identification on the morning of August 12, when it is 9.5 degrees to the upper right of the planet.  The stars Castor and Pollux appear above Mars.

Mercury

merc_lune_150816

Always difficult to see, Mercury briefly appears in the western evening sky during mid-month.  The moon appears 5 degrees to the left of Mercury on August 16.  Use binoculars to locate the moon.  Move the binocular so that the moon appears on the left side of the visible field of view, Mercury should appear on the right side of the view.  Then try to locate each without optical help.

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