SKY HAPPENINGS

The Sky for August 2011
By Faylene Roth

DAYLENGTH
Daylength shortens by one hour five minutes this month. Sunrise occurs 26 minutes later by the end of the month and sunset arrives 39 minutes earlier. The times for sunrise and sunset are calculated for a flat horizon, so actual times may vary depending upon the surrounding landscape. Twilight extends the period of usable light about 45 minutes on each end of the day. Civil twilight provides adequate light for most activities for one-half hour before sunrise and after sunset. Nautical twilight covers the 30-minute period before civil twilight in the morning and after civil twilight in the evening. In the morning sky light spreads from the eastern horizon across the sky slowly revealing the vivid colors of the local landscape. During evening twilight color and details of the landscape fade from view. In the final phase of twilight—astronomical twilight-- the skies are dark overhead but light lies along the horizon for another half hour.

MOON HAPPENINGS
August 6 – First Quarter Moon sets soon after midnight.
August 13 – A slightly waning Full Moon rises
at 8:00pm.
August 21 – Last Quarter Moon rises shortly before midnight.
August 28 – New Moon occurs at 9:04pm..

METEOR EVENTS
Take advantage of the moonless night of August 1 to view the Capricornid Meteor Shower. Its radiant, Capricornus, can be found along the band of the zodiac. Look for Scorpius, the scorpion, low in the eastern sky. Sagittarius (posing as a teapot) follows to the left with the Milky Way swirling down between the two constellations. Capricorn (shaped somewhat like a boomerang) rises to the left of Sagittarius, followed soon by Aquarius. The Capricornids are not the most prolific meteor shower but they produce some of the brightest meteors of the major meteor showers. Viewing can begin at the end of astronomical twilight, but the best time is still after midnight. By then, some of the leftovers from the Delta Aquarid Meteor Showers (radiant Aquarius) may also be visible.

A full moon washes out one of the best meteor showers of the year—the Perseids. They peak on the night of August 12/13, which is the night before this month’s full moon. However, with up to 60 meteors per hour at its peak, the best and brightest will still be visible. Viewing will be good from August 9 - September 20. The very best opportunity may be in the early morning hours before astronomical twilight. Perseus (radiant for this shower) follows Cassiopeia across the northern sky.

DARK SKY GAUGE
The four stars of the Little Dipper’s basket provide a gauge for measuring the darkness of the night sky. The Little Dipper is much fainter than its companion, the Big Dipper, which is comprised mostly of magnitude +2 stars. The basket of the Little Dipper has one magnitude +2 star and one +3 star. They form the outer edge of the basket. The two inner stars of the basket are magnitude +4 and +5. If all four stars are visible, then the quality of the night sky is good and faint +5 and +6 stars are visible below the North Star (Polaris) which is a +2 magnitude star. A +6 magnitude marks the limit of visibility for naked-eye stargazing.

Note: Hold your hand at arm’s length to measure apparent distances in the sky. The width of the little finger approximates 1.5 degrees. Middle, ring, and little finger touching represent about 5 degrees. The width of a fist is about 10 degrees. The fist with the thumb extended at a right angle equals 15 degrees. The hand stretched from thumb to little finger approximates 20-25 degrees. The diameter of both the full moon and the sun spans only 0.5 degree. Adjust for the size of your hand.

Primary Sources: USGS; U.S. Naval Observatory;
Your Sky at http://www.fourmilab.ch/yoursky/

To find out when the space shuttle and International Space Station are visible
from your location, go to: http://spaceflight.nasa.gov/realdata/sightings/index.html and click on Sighting Opportunities.

VISIBLE PLANETS
Jupiter - Look for Jupiter in the eastern sky around midnight in Aquarius. It rises an hour or two after Saturn sets, depending upon the surrounding landscape. Find it high overhead in morning twilight. (Magnitude -2.7)

Mars - Early morning twilight offers the best chance to see Mars. Look for a red, albeit faint, disk about 40 to 60 degrees below Jupiter (see Note below regarding apparent distances in the sky). On the morning of August 25, find Mars to the right of the twin stars of Gemini, with a thin crescent moon to its right. (Magnitude +1.4)

Saturn - The golden planet moves this month to a position low on our western horizon and sets before midnight. It remains paired with the star Porrima, both to the right of the bright blue star Spica (all in Virgo). Be sure to enjoy its presence now because it disappears from view at month’s end. (Magnitude +0.9)

Note: Apparent magnitude values range from -4 to +6 for most planets and visible stars. The lower the value the brighter the object. A decrease of 1.0 magnitude is 2.5 times brighter.

Follow the Milky Way from Cassiopeia in the northern sky through Cygnus and the Summer Triangle and on to Sagittarius in the southern sky. Gaze through the stars at the western edge of Sagittarius and into the center of our galaxy
—over 26,000 light years away..

Hold the star chart high above your head and match the compass directions to the direction you are facing. Adjust the star chart by orienting Ursa Major (Big Dipper) to match its position in the sky.

The star chart approximates the sky from astronomical twilight to midnight. As the night and month progresses, the constellations shift toward the northwest. The celestial equator is measured in hours (h).
The ecliptic is measured in degrees.