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Sky Happenings
Moab UT (at City Hall)
38O34’ N Latitude 109O33’ W Longitude
4048 ft - 1234 m




The Sky for August 2009

By Faylene Roth


Sunrise and Sunset Times for
August 2009
Sunrise and Sunset for Moab in August, 2009

DAYLENGTH
The period from sunrise to sunset decreases by 66 minutes during August. Civil twilight provides 30 minutes of strong daylight after sunset. Shapes and color fade from the landscape during the next 30-40 minutes of nautical twilight. Astronomical twilight continues another half hour as the last rays of the sun recede from the sky. The reverse progression occurs at dawn. Actual time of sunrise and sunset may vary depending upon the surrounding landscape.

MOON HAPPENINGS
August begins with a waxing gibbous moon high in the evening sky. August 5 a full moon rises at 8:16pm. August 6 the moon and Jupiter rise together over the LaSals soon after 9:00pm. The last quarter moon occurs August 13. After midnight the moon rises with the Pleiades and over the next few hours occludes it from view. August 16 the waning crescent moon and Mars rise together after 2:00am, followed a few hours later by Venus. August 18, a thin crescent moon rises in the morning twilight with Venus. A new moon occurs August 20. August 22 a slim waxing crescent moon reappears on the western horizon with Mercury and Saturn. August 23 the crescent moon appears at twilight a little higher in the southwestern sky with Spica (Virgo). The first quarter moon occurs August 27. Later that night a gibbous moon occults Antares (Scorpius) in the southern sky.

METEOR EVENTS
During the first few weeks of August watch the radiants of Aquarius and Capricornus for activity from the Southern Delta Aquarid Meteor Shower and the Capricornid Meteor Shower. Aquarius and Capricornus will be high in the southern sky after midnight, but bright moonlight dampens viewing conditions.
Earth passes through the Perseid Meteor Shower during the first three weeks of August. Despite a waning gibbous moon, the Perseids may still provide viewers with up to 20-30 visible meteors per hour. The night and early morning hours of August 12-13 mark the peak of this event. Its radiant, Perseus, rises in the northeastern sky below Cassiopeia. Best viewing is from the end of astronomical twilight until the moon rises around midnight and again before morning twilight.
After midnight August 20 watch the vicinity of Cygnus for smoky meteor trails from the Kappa Cygnid Meteor Showers. The Southern Delta Aquarids resurge with a second peak August 21-23. A new moon offers excellent viewing conditions. The month ends with the Andromedid Meteor Showers. Andromeda will be overhead after midnight. Best viewing is August 31 after 2:00am.

TRACKING THE MOON
The full moon on August 5 rises in the southeastern sky and sets in the southwestern sky the following morning. Notice over the next two weeks that the waning moon appears farther north on the horizon each day both when it rises and when it sets. By August 20 the new moon darkens the sky for a few days. When the waxing crescent moon reappears in the evening sky, it will have moved southward. Over the next two weeks notice that each night the moon sets a little farther south on the horizon. The north-south movement of the moon each month mimics the seasonal pathway of the sun across the sky. The sun takes one year to traverse its pathway, whereas the moon progresses through its cycle every month. To predict how high in the sky the moon will be later in the month, it’s necessary to know when the moon was at its northernmost node or southernmost node. Over the following two weeks it moves towards the opposite node. The turning points are called lunar standstills.

Earth’s equator is tilted 23.5 degrees from the plane of its orbit around the sun, which is known as the ecliptic. The plane of the moon’s orbit around the earth is offset five degrees from the plane of the ecliptic. This variation produces an 18.61 year cycle of high-low moon, or lunar standstills. At one extreme the moon rises five degrees north of the sun’s position on the summer solstice, or 28.5 degrees north of the equator. Two weeks later it rises five degrees south of the sun’s position on the winter solstice, or 28.5 degrees south of the equator. Over the next 9.3 years the extremes of the moon’s position north or south of the equator shrinks to five degrees less than the 23.5 degree tilt of the earth’s equator to the ecliptic. At mid-cycle the north-south range of the moon in the sky would be only 18.5 degrees north or south of the equator. During the next half of the cycle the north-south extremes of the moon’s pathway start to widen again. The last maximum lunar standstill occurred in 2006. Over the next six years the northernmost and southernmost positions of the moon each month will become less extreme.

Note:
Hold your hand at arm’s length to measure apparent distances in the sky. Adjust for the size of your hand. 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 hand stretched from thumb to little finger equals 20 degrees. The diameter of both the full moon and the sun spans only 0.5 degree.


VISIBLE PLANETS
Mercury - August 22 Mercury reaches greatest elongation, 27 degrees east of the sun. Observers need a high vantage point to view Mercury low on the horizon. Cues for sighting Mercury are a thin crescent moon and the yellow orb of Saturn to the south. Binoculars or telescope would be useful. (Magnitude 0)

Jupiter - This month Jupiter dominates the evening sky. August 14 it reaches opposition from the sun, the point in its orbit that is on the side of the earth away from the sun, and its closest approach to Earth. Jupiter shines brighter this month than it will for the next year. It rises soon after sunset with Capricornus and remains visible until it sets in the morning twilight. Find it low in the southern sky. (Magnitude -2.7)

Mars - Look for a tiny red disk rising in the northeastern sky between 2:00am and 3:00am with Taurus. August 29 Mars appears one degree south of the Beehive Cluster, a fuzzy cloud visible with the unaided eye in Taurus. (Magnitude +1)

Saturn - By August 10 the rings of Saturn present an edge-on orientation to Earth which renders them invisible. This presentation occurs on a 14-15 year cycle. It provides a good opportunity to view Saturn’s moons with a telescope. By month’s end Saturn is too low on the horizon to be visible. (Magnitude +1.3)

Venus - Look for Venus in the northeastern sky after 4:00am. Venus is in its crescent phase with 35 percent of its face reflecting light towards Earth. August 17 a thin crescent moon rises just ahead of Venus. Castor and Pollux, twin stars of Gemini, perch above them. (Magnitude -3.9)

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.

Primary Sources: USGS, U.S. Naval Observatory, http://www.fourmilab.ch/yoursky/

MAJOR CONSTELLATIONS this MONTH

Overhead
Aquila
Cygnus
Hercules
Lyra


Northward
Cassiopeia
Cepheus
Draco
Ursa Major
Ursa Minor


Eastward
Andromeda
Aquarius
Pegasus
Perseus

Southward
Capricornus
Ophiucus
Sagittarius
Scorpius

Westward
Bootes
Corona Borealis
Libra
Virgo

Andromeda follows Cassiopeia and Pegasus into the eastern sky as Bootes and Scorpius hover on the western horizon. The Summer Triangle is overhead.

Night Sky for Moab in August 2009

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 night sky from astronomical twilight to midnight. As the night and the month progress, the constellations will shift toward the northwest.

 
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