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SKY HAPPENINGS

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

The Sky for September 2013
By Faylene Roth

 

Sunrise-Sunset
For September 2013

DATE

SUNRISE

SUNSET

1

6:48am

7:48pm

2

6:49am

7:46pm

3

6:50am

7:45pm

4

6:50am

7:43pm

5

6:51am

7:42pm

6

6:52am

7:40pm

7

6:53am

7:38pm

8

6:54am

7:37pm

9

6:55am

7:35pm

10

6:56am

7:34pm

11

6:57am

7:32pm

12

6:57am

7:31pm

13

6:58am

7:29pm

14

6:59am

7:27pm

15

7:00am

7:26pm

16

7:01am

7:24pm

17

7:02am

7:23pm

18

7:03am

7:21pm

19

7:04am

7:19pm

20

7:04am

7:18pm

21

7:05am

7:16pm

22

7:06am

7:15pm

23

7:07am

7:13pm

24

7:08am

7:11pm

25

7:09am

7:10pm

26

7:10am

7:08pm

27

7:11am

7:07pm

28

7:12am

7:05pm

29

7:12am

7:04pm

30

7:13am

7:02pm

The Great Square forms the body of Pegasus the flying horse. It provides a gauge of the quality of darkness of the night sky. Ten to 13 visible stars within the square indicates good dark skies.

DAYLENGTH
The evening sky darkens rapidly this month as summer twilight fades nearly two minutes earlier each day. By month’s end the period of daylight from sunrise to sunset will be less than 12 hours long. Twilight adds an additional period of usable light. At dusk adequate light for most activities continues for about 30 minutes after sunset—a period called civil twilight. Nautical twilight begins once the sun has dipped six degrees below the horizon. During this half-hour period the overhead sky darkens while color and detail disappear from the surrounding landscape. When the sun drops below 12 degrees, astronomical twilight begins during which the residual light of sunset fades from the horizon. Astronomical twilight ends and night begins when the sun sinks 18 degrees below the horizon. The reverse progression applies to dawn.

AUTUMN EQUINOX
An imaginary line called the ecliptic traces the path of the sun across the sky relative to the background stars. Earth’s orbit around the sun creates the seasons because the equator is tilted from the plane of the ecliptic at an angle of 23.5 degrees. The angle and direction of the tilt does not change as the earth travels around the sun, but it does present a different face of the earth towards the sun. In winter the northern hemisphere tilts away from the sun; in summer it tilts towards the sun. In spring and fall—at the equinox—both hemispheres receive the same amount of light because the sun shines perpendicular to the equator. An extension of the earth’s equator into the celestial sphere creates the celestial equator. The equinox occurs at the point in the earth’s orbit where the plane of the ecliptic intersects the celestial equator. This year the intersection occurs on September 22 at 2:44pm MDT. Sunrise will be due east and sunset will be due west. The length of day and night would be equal if it were not for the effect of refraction which means that light bends around the curvature of the earth, making the sun visible before it crests the horizon.

MOON HAPPENINGS
September 5–New Moon occurs at 5:36am.
September 12–First Quarter Moon sets soon after midnight.
September 19–Full Moon occurs 5:13am and rises at 7:21pm.
September 26–Last Quarter Moon rises soon after midnight.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

ZODIACAL LIGHT
Imagine sunlight streaming through a window and illuminating dust particles floating in the room. In the same way, the rising and setting sun illuminates dust particles present in the inner solar system. Near the autumnal equinox, the sun’s rays shoot high into the sky before sunrise and after sunset and project a beam of light through ambient dust particles. Look for a cone-shaped beam of white light that can extend as far as 60° above the horizon. It is called the zodiacal light because it appears within the zodiac—a band across the sky that represents the plane of the solar system with the ecliptic at its center. Look for the zodiacal light in the morning sky about 1-2 hours before astronomical twilight begins.

METEOR EVENTS
September offers no major meteor showers, but it is a good month for sporadic meteor events. Sporadic meteors originate from debris left over from interplanetary collisions within our solar system rather than debris associated with comet trails. Early morning provides the best viewing for meteors because the direction of the earth’s rotation converges with the direction of the earth’s orbit at that time. Meteors approach as the earth moves into the residual dust left by earlier collisions. Expect to see 10-20 meteors an hour from random directions during September’s sporadic displays.

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 during the middle of the night in the northeastern sky near the twin stars of Gemini. It dominates the early morning sky rivaled only by Orion and Sirius the Dog Star trailing Orion in the southeastern sky. (Magnitude -1.9)

Mars begins September near the Beehive Cluster (Praesepe) in Cancer. By the end of the month it moves into Leo. Mars rises in the pre-dawn sky ranging 15°-30° below Jupiter as the month progresses. Look for a small red-orange disk that does not twinkle. (Magnitude +1.8)

Saturn appears in the evening sky above Venus, drifting closer to the horizon each evening. By September 23 Saturn sets with Venus. During the last week of the month it sets before Venus. (Magnitude +1.2)

Venus dominates the evening twilight but drops below the horizon as astronomical twilight fades. On September 8 it appears about three degrees below Saturn and within one-half degree of a waxing crescent moon. (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
Lyra

Northward
Cassiopeia
Cepheus
Draco
Ursa Major
Ursa Minor

Eastward
Andromeda
Aquarius
Pegasus
Perseus
Pisces


Southward
Capricornus Sagittarius
Scorpius

Westward
Boötes
Corona
Borealis Hercules
Libra
Ophiucus
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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