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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 2013
By Faylene Roth

 

Sunrise-Sunset
For August 2013

DATE

SUNRISE

SUNSET

1

6:20am

8:28pm

2

6:21am

8:27pm

3

6:22am

8:26pm

4

6:23am

8:25pm

5

6:24am

8:24pm

6

6:25am

8:23pm

7

6:26am

8:22pm

8

6:26am

8:21pm

9

6:27am

8:19pm

10

6:28am

8:18pm

11

6:29am

8:17pm

12

6:30am

8:16pm

13

6:31am

8:14pm

14

6:32am

8:13pm

15

6:33am

8:12pm

16

6:34am

8:11pm

17

6:34am

8:09pm

18

6:35am

8:08pm

19

6:36am

8:07pm

20

6:37am

8:05pm

21

6:38am

8:04pm

22

6:39am

8:02pm

23

6:40am

8:01pm

24

6:41am

8:00pm

25

6:42am

7:58pm

26

6:42am

7:57pm

27

6:43am

7:55pm

28

6:44am

7:54pm

29

6:45am

7:52pm

30

6:46am

7:51pm

31

6:47am

7:49pm

The Great Square of Pegasus provides a gauge of the darkness of the night sky. Very dark skies reveal more than 13 stars within the square. If skies are dark enough, the Andromeda Galaxy can be seen as a fuzzy blob near the northeast corner of the square in Pegasus. Locate the two sweeping arcs that extend northward from the northeast corner star. On the lower arc move northward two stars. Follow a perpendicular line upward through two fainter stars. Our nearest galaxy neighbor appears as a blur above and to the right of the highest faintest star.

DAYLENGTH
The period between sunrise and sunset decreases by 66 minutes in August. By month’s end the sun rises 27 minutes later and sets 39 minutes earlier. Twilight progresses across the morning and evening skies in three stages, adding additional light for outdoor activities. Civil twilight lasts about one-half hour after sunset. Nautical twilight continues another 30-45 minutes with the darkening of the overhead sky and color and shapes still apparent nearby. Astronomical twilight begins when color and detail disappear from the surrounding view and ends when the sky darkens along the horizon. The reverse progression applies before sunrise.

DOG DAYS OF SUMMER
The brilliant star in early morning twilight on the southeastern horizon is Sirius, Dog Star of the constellation Canis Major. Sirius is associated with the winter sky when it rises early evening below the familiar 3-star belt of Orion. Sirius rises with the sun around the beginning of August. Since it appears to be the brightest star seen from the northern hemisphere, ancient Egyptians and Romans believed that it added to the heat of late summer months as it passed across the daytime sky in conjunction with the sun. Thus, the 20 days before conjunction and the 20 days after conjunction became known as the dog days of summer. Astronomers now know that none of the stars are near enough to Earth to increase its temperature. They also know that the time of conjunction of Sirius with the sun gradually changes over time due to precession of the equinoxes (aka wobble of Earth’s axis).

MOON HAPPENINGS
August 6 – New Moon occurs at 3:51pm.
August 14 – First Quarter Moon sets soon after midnight.
August 20 – Full Moon occurs 7:45pm and rises at 7:40pm. August 28 – Last Quarter Moon rises soon after midnight.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

METEOR EVENTS
One of the best meteor showers of the year—the Perseids—is active throughout the first three weeks of August. Its radiant lies between Perseus and Cassiopeia, but meteors may be seen in all regions of the sky. Peak viewing this year occurs on the nights of August 11/12 and 12/13, with the first night more promising. A waxing crescent moon sets before midnight darkening the skies for optimal viewing between midnight and dawn. As Perseus moves higher in the sky, we have a broader view of the meteor field. Up to 50 or more meteors per hour are often reported.

Note: Hold your hand at arm’s length to measure apparent distances in the sky. The width of the little finger approximates 1.5 ̊. Middle, ring, and little finger touching represent about 5 ̊. The width of a fist is about 10 ̊. The fist with the thumb extended at a right angle equals 15 ̊. The hand stretched from thumb to little finger approximates 20 ̊-25 ̊. The diameter of both the full moon and the sun spans only 0.5 ̊. 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 rises in the eastern sky before astronomical twilight, by month’s end around 3:00am. On the mornings of August 3-5, Jupiter and the waning crescent moon provide landmarks for Castor (Gemini) to the north and Mars and Mercury below. The crescent moon wanes as it moves down the line of planets over the three-day period. (Magnitude -1.7)

Mars appears in the morning sky as a very small reddish point of light 5° below Jupiter. Pollux (Gemini) appears north of Mars and below Castor (the other Gemini twin). On the morning of August 3 the waning crescent moon appears above Mars. The following morning it appears below. (Magnitude +1.8)

Mercury rises about one and one-half hours before sunrise during the first few weeks. It brightens to -1.4 as it approaches perihelion (point closest to sun) on August 12 and reaches superior conjunction (between Earth and Sun) on August 24. Best viewing occurs August 3-5 when the waning crescent moon passes first Jupiter, then Mars, and fades below and to the north of Mercury. By mid-month the planet is no longer visible. (Magnitude +0.1)

Saturn sits within a large L-shape in the southwestern evening sky. Follow the arc of the Big Dipper’s handle to orange-tinted Arcturus (Boötes). Saturn hangs 60° below. The lower bar of the L ends 10° to the right with blue-tinged Spica (Virgo). On August 12 a waxing crescent moon appears between Saturn and Spica. Saturn sets before midnight after the first few days of the month. (Magnitude +1.1)

Venus remains visible in the evening sky throughout the month. It sets as astronomical twilight fades from the western horizon. It sets earlier each evening which brings it closer to Saturn on its southern side. On August 9 a waxing crescent moon appears to the lower left of Venus. (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.

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
Boötes
Corona
Borealis
Libra
Virgo

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.

Sky Map for Moab Feb 2013
 
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