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SKY HAPPENINGS

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

The Sky for July 2013
By Faylene Roth

 

Sunrise-Sunset
For July 2013

DATE

SUNRISE

SUNSET

1

5:58am

8:46pm

2

5:58am

8:46pm

3

5:59am

8:46pm

4

5:59am

8:46pm

5

6:00am

8:46pm

6

6:00am

8:45pm

7

6:01am

8:45pm

8

6:02am

8:45pm

9

6:02am

8:44pm

10

6:03am

8:44pm

11

6:04am

8:44pm

12

6:04am

8:43pm

13

6:05am

8:43pm

14

6:06am

8:42pm

15

6:06am

8:42pm

16

6:07am

8:41pm

17

6:08am

8:41pm

18

6:09am

8:40pm

19

6:09am

8:39pm

20

6:10am

8:39pm

21

6:11am

8:38pm

22

6:12am

8:37pm

23

6:13am

8:36pm

24

6:13am

8:36pm

25

6:14am

8:35pm

26

6:15am

8:34pm

27

6:16am

8:33pm

28

6:17am

8:32pm

29

6:18am

8:31pm

30

6:18am

8:30pm

31

6:19am

8:29pm

DAYLENGTH
The period of daylight shortens by 39 minutes this month. However, with the sun still far northward on the ecliptic, twilight continues to linger for nearly two hours both before sunrise and after sunset. Twilight progresses through three stages. Civil twilight begins at sunset and continues until the sun reaches six degrees below the horizon. Adequate light for most activities remains across the sky. During the next stage, called nautical twilight, the overhead skies darken. First magnitude stars pop into view, but light lingers on the western horizon where only the brightest planets are likely to be seen. Nautical twilight continues until the sun descends to twelve degrees below the horizon. During July nautical twilight lengthens to nearly 40 minutes beyond civil twilight. Color and detail fade from the horizon. Astronomical twilight then begins. Once the sun reaches 18 degrees below the horizon, truly dark skies overtake the night sky (10:45pm on July 1/10:15pm by month’s end) and reveal the grandeur of the Milky Way.

CREPUSCULAR SUNRAYS
Increased amounts of dust, smoke, water vapor, and aerosols in summer skies create conditions for crepuscular sunrays. Look for these visible rays of light shooting out from the horizon from gaps in the clouds or between cracks in the mountain or canyonlands skyline. The rays appear to radiate from a focal point, but they are actually parallel rays. They can be seen either morning or evening during civil twilight when conditions are right. Sometimes they are quite colorful and often a faint reflection appears on the opposite side of the sky.

APHELION
On July 5 at 9:00am the Earth reaches its farthest point from the sun (aphelion) for the year but don’t expect to feel any cooler. The tilt of the northern hemisphere towards the sun allows so much heat to reach the Earth’s surface that the extra three million miles goes unnoticed. Aphelion will not always occur at this time of year. Due to precession of the equinoxes (a wobble in the direction of the Earth’s axis), the time of aphelion is delayed by about 25 minutes each day, which amounts to one day every 58 years. The current timing of aphelion does contribute to the length of the seasons. Earth’s velocity slows as it passes through aphelion which lengthens the summer season in the northern hemisphere by about five days compared to its winter season. Conversely, the southern hemisphere experiences a longer winter and a shorter summer.

MOON HAPPENINGS
July 8 – New Moon occurs at 1:14am.
July 15 – First Quarter Moon sets soon after midnight.
July 22 – Full Moon occurs 12:15pm and rises at 8:27pm.
July 29 – Last Quarter Moon rises soon after midnight.
(The time of moonrise and moonset assumes a flat horizon.
Actual time may vary.)

METEOR EVENTS
Predictable meteor activity begins again with the Delta Aquarid Meteor Shower. It peaks July 27-30 as a gibbous moon fades towards last quarter phase. The Delta Aquarid Shower produces faint meteors fairly consistently from mid-July to mid-August, so look during periods when the moon is absent from the sky or opposite its radiant in Aquarius. Best viewing occurs when the radiant is overhead which begins around midnight in Canyon Country.

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 – Midmonth Jupiter emerges from its sojourn beyond the sun and reappears in the morning sky. Look for it due east in early twilight below Mars. A high vantage point improves chances to see it. (Magnitude -1.6)

Mars - Early morning stargazers may notice the reddish star Aldebaran (in Taurus’s horn) in the eastern sky. Look for the red planet Mars about 60 degrees below just before twilight brightens the sky. On July 22 Mars and Jupiter rise within one degree of one another. Within a few days Mars will lag behind Jupiter. (Magnitude +1.7)

Saturn – As nautical twilight spreads across the evening sky, look overhead. Orange-hued Arcturus (0 magnitude) will be the first star to pop into view—high but west of the meridian. Within a few seconds, Saturn appears about 60 degrees below. Its steady golden light distinguishes it from the white twinkling light of Spica (Virgo) which soon appears about 10 degrees west of Saturn. (Magnitude (+0.9)

Venus – Watch the western evening sky as brilliant Venus maneuvers around 1st magnitude Regulus (Leo). On July 22 they are within two degrees of one another. (Magnitude -3.8)

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
Boötes
Corona Borealis
Hercules
Ophiucus

Northward
Cassiopeia
Cepheus
Draco
Ursa Major
Ursa Minor

Eastward
Aquila
Cygnus
Lyra
Pegasus


Southward
Libra
Sagittarius
Scorpius

Westward
Corvus
Leo
Virgo

Look for the Summer Triangle high in the eastern sky—formed by 0-magnitude Vega (Lyra) and 1st magnitude stars Deneb (Cygnus) and Altair (Aquila). Overhead 0-magnitude Arcturus (Boötes) outshines Vega. Hercules can be identified by the blockish trapezoid halfway between Arcturus and Vega. The Great Square of Pegasus soon rises above the eastern horizon.


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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