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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 2012
By Faylene Roth



DAYLENGTH

The long periods of summer daylight shorten by 71 minutes in September. Notice the change is not evenly distributed. Earlier sunsets advance more rapidly than later sunrises because of the Earth’s position in its orbit. Twilight, too, fades faster since the earth’s tilt no longer faces directly towards the sun. Civil twilight extends usable daylight by 30 minutes after sunset. Nautical twilight continues another half hour as shapes and color disappear from the landscape. In a final half hour of astronomical twilight, the last rays of sunlight fade from the sky. The reverse progression applies to dawn.

DATE

SUNRISE

SUNSET

1
6:48am
7:47pm
2
6:49am
7:46pm
3
6:50am
7:44pm
4
6:51am
7:43pm
5
6:51am
7:41pm
6
6:52am
7:40pm
7
6:53am
7:38pm
8
6:54am
7:37pm
9
6:55am
7:35pm
10
6:56am
7:33pm
11
6:57am
7:32pm
12
6:58am
7:30pm
13
6:58am
7:29pm
14
6:59am
7:27pm
15
7:00am
7:25pm
16
7:01am
7:24pm
17
7:02am
7:22pm
18
7:03am
7:21pm
19
7:04am
7:19pm
20
7:05am
7:17pm
21
7:06am
7:16pm
22
7:06am
7:14pm
23
7:07am
7:13pm
24
7:08am
7:11pm
25
7:09am
7:10pm
26
7:10am
7:08pm
27
7:11am
7:06pm
28
7:12am
7:05pm
29
7:13am
7:03pm
30
7:14am
7:02pm

MOON HAPPENINGS
Sept 8 – Last Quarter Moon rises soon after midnight.
Sept 15 – New Moon occurs at 8:11pm.
Sept 22 – First Quarter Moon sets soon after midnight.
Sept 29 – Full Moon occurs at 9:19pm and rises at 6:38pm.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

AUTUMN EQUINOX
At 8:49am, September 22, the sun’s apparent pathway through the sky (aka the ecliptic) crosses the celestial equator in Virgo (see the star map) which marks the end of summer and beginning of the fall season. The Harvest Moon—the full moon nearest to the autumnal equinox—occurs one week later. According to tradition, the full moon nearest the equinox allowed farmers to continue to harvest beyond sunset for several days without a period of darkness between sunset and moonrise. The time from one moonrise to the next can vary from 20 minutes to over one hour due to the earth’s tilt away from the plane of its orbit and the position of the moon within the band of the ecliptic. However, near the equinox the effect of the tilt is minimized which reduces the time from one moonrise to the next to about 30 minutes for several days.

METEOR EVENTS
September has no major meteor showers, but it is a good month for viewing sporadic meteor events. Sporadic meteors originate from the debris left over from interplanetary collisions within our solar system. (Most meteor showers, like the Perseids, Leonids, etc., are associated with particle trails left in the wakes of comets.) Early morning, before twilight, 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 are then approaching us as the earth moves into the residual dust left by earlier events. Expect to see 10-20 meteors an hour from random directions during September’s sporadic displays. That’s double the number of sporadic events produced in the spring and early summer. Most meteors burn up in the atmospheric layer known as the mesosphere. The mesosphere measures about 20 miles thick and sits 30 miles up atop the ozone layer at the top of the stratosphere.

Jupiter – The largest and second brightest planet remains a dominant feature of the morning sky throughout the rest of the year. Jupiter rises around midnight (about an hour before by month’s end) and climbs to an overhead position by morning twilight. Find it between the horns of Taurus with bright red Aldebaran below and bluish stars of the Pleiades above. On the night of September 7/8 a third-quarter waning moon appears less than one degree below Jupiter. (Magnitude -2.6)

Mars – The red planet continues to fade as it recedes from Earth and sets with evening twilight. Look for a red-hued orb forming the tip of a triangle with Saturn and 1st magnitude blue star Spica (Virgo) in early September. Mars moves southeastward across Libra towards Scorpius during the last half of the month. Its redness helps identify it in this sparsely-lighted region of the sky as it moves towards the head of Scorpius and 1st magnitude red star Aldebaran at the scorpion’s heart. (Magnitude +1.2)

Saturn - The golden planet sets with early evening twilight by midmonth and re-emerges in the morning sky in November. Look for it during the first week of September low on the western horizon in Virgo just above Spica. On the night of September 17 a thin waxing crescent moon hangs below Spica and Saturn on the western horizon. (Magnitude +0.8)

Venus – Each night, as Jupiter rises earlier, Venus rises later, so the distance between the two brightest planets increases from about 45 degrees to 75 degrees over the month. On September 1,Venus rises less than 10 degrees below 1st magnitude Pollux (Gemini). By September 12, it appears in the center of Cancer with a thin waning crescent moon within four degrees to the south and Praesepe (Beehive Cluster) to its north. At the end of the month, it is rapidly approaching 1st magnitude star Regulus (Leo). (Magnitude -4.1)

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.

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

Bootes
Corona Borealis
Hercules
Libra
Ophiucus
Virgo

Scorpius lies along the southwestern horizon; the Summer Triangle appears overhead; the Great Square of Pegasus dominates the eastern skies; Perseus and Andromeda claim the northeastern skies; the lone star above the southern horizon is Fomalhaut (“mouth of the fish”) situated at -30 degrees South latitude in the constellation Pisces Austrinus (“southern fish”).


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.

skychart for Sept 2012
 
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