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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 2010

By Faylene Roth


Sunrise and Sunset Times for
July 2010

DAYLENGTH
The period of daylight starts to decrease this month. The sun rises 21 minutes later and sets 16 minutes earlier by the end of the month. The decrease in length of the day occurs because the sun’s apparent path in the sky moves southward after the Summer Solstice. The bulge in the Earth’s circumference near the equator results in later sunrises and earlier sunsets. The change in sunrise and sunset is not equally distributed between morning and evening, because the direction of Earth’s rotation on its axis and its revolution around the Sun are eastward. As the Earth approaches the elliptical end of its orbit before the Solstice, it requires less than one complete rotation to reach the next sunrise or sunset. The effect is earlier sunrises and sunsets. The effect after the Solstice is later sunrises and sunsets. As the Earth’s orbit carries it away from the elliptical end of the orbit, it must exceed one complete rotation before the next sunrise or sunset. In the morning there is a cumulative effect towards later sunrises. In the evening the two forces are at odds, which dampens the effect of later sunsets. Extended summer twilight continues until after 10:00pm throughout the month. (The time of sunrise and sunset assumes a flat horizon. Actual time may vary depending upon the landscape.)

MOON HAPPENINGS

July begins with a waning gibbous moon rising after midnight in most locations. On July 3 the moon and Jupiter travel the night sky together and shine brightly in the morning twilight. The last quarter moon occurs July 4. A new moon arrives July 11. A thin waxing sliver of moon reappears below Venus on July 14. Mars and Saturn are above and to the left. The first quarter moon occurs July 18. On July 20 look for Antares (Scorpius) to the left of a waxing gibbous moon. A full moon rises July 25 at 8:23pm. On July 30 a waning gibbous moon again pairs with Jupiter in the night sky, rising before midnight. (The time of moonrise and moonset assumes a flat horizon. Actual time may vary depending upon the landscape.)

COMET VIEWING

On July 2 scan low on the NNE horizon for a fuzzy apparition in the morning twilight and again on the NNW horizon that evening. Comet McNaught makes its closest approach to the sun on this day. Astronomers have been watching the comet for some time and expect it to be bright enough to view with the unaided eye. Use binoculars to look for a tail trailing away from the sun. Comet McNaught should be visible throughout the week.

METEOR EVENTS
Look for meteors from the Omicron Draconid Meteor Showers on July 16. The radiant is from Draco which is a circumpolar constellation. That means the meteors will be visible all night once the moon sets at 11:35pm. The Alpha Capricornids are active July 23-30 in the southern sky. In spite of a nearly full moon, the fireballs that occasional flare from this meteor shower would still be visible. A waning full moon will likely wash out the Delta Aquarid Meteor Showers this year. Best chance for viewing will be after 11:00pm, July 27, continuing through the night. Meteor activity in the northeastern sky during the latter part of July are previews of what is to come with the Perseid Meteor Showers in August.

APHELION
If July 6 is a hot day, be grateful that the sun is at its farthest point from Earth—a distant 94,513,144 miles. That is 3% farther than it is at perihelion which occurs in January. The heat of the day is the result of the Earth’s tilt of 23.5 degrees from the plane of its orbit. That puts the face of the northern hemisphere directly in line with the intense radiation of the sun.

LOCAL STAR COUNT
Join Red Rock Astronomers at Old City Park on Sunday, July 18, at 9:10pm for a tour of the night sky and telescope viewing. Meet at the southwest corner of the park below the bandstand and the duck pond. Bring a chair or blanket for easy viewing. Sponsored by WabiSabi and all ages are welcome. For information call 259-4743 or 259-3313.

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.

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 - Late night and early morning skies belong to Jupiter this month. Look for it in the eastern sky soon after 1:00am during the first half of the month. By the end of July it appears around midnight. Mercury, Venus, and Mars have all set by the time Jupiter rises. Saturn, the last of the visible planets, sets in the western sky one minute after Jupiter rises throughout most of the month. However, due to the rim effect, Saturn disappears from view early and Jupiter’s appearance is delayed. Jupiter is still visible high in the southern sky at morning twilight. Its position is in Pisces just south of the Celestial Equator. (Magnitude -2.8)

Mars - Track the eastward movement of Mars across the night sky this month. In June, Mars was bound to Regulus (Leo); but even then it passed from Regulus’s right to its left. This month it leaves the constellation Leo behind and enters Virgo on July 19. Follow the red planet as it rapidly approaches Saturn’s bright yellow orb. It is easy to understand why the ancient Greeks called these orbiting bodies “planets” which means “wanderers.” Mars is receding from Earth as it heads towards the far side of the sun. Its magnitude fades to +1.5 by month’s end. (Magnitude +1.4)

Mercury
- By month’s end the elusive planet Mercury joins the string of stellar objects in the western sky. It outshines nearby first magnitude star Regulus, both very low on the horizon in Leo. Look for it within one hour of sunset from a high vantage point. (Magnitude -0.4)

Saturn
- The brilliant yellow orb of Saturn remains anchored in Virgo. It begins a slight drift towards Spica this month because its retrograde motion has ended. Saturn’s position is a little north of the Celestial Equator. It is the highest of the planets in the western sky. It will set around midnight, soon replaced in the eastern sky by rising Jupiter. (Magnitude +0.5)
Venus - This month it is Venus rather than Mars that pairs with Regulus (Leo). On the evening of July 9 the two appear about one degree apart. Venus then moves eastward away from Regulus. By month’s end, it approaches Mars and Saturn near Virgo’s boundary. Venus’s position in the sky is tied to its orbit around the sun. As the sun sets earlier so will Venus. It appears lower in the sky each evening. Its background stars also change nightly. Each night the stars rise four minutes earlier. That causes the background stars of Leo to move farther west of Venus’s position each night. (Magnitude -4.0)
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
Bootes
Corona Borealis
Hercules
Ophiucus


Northward
Cassiopeia
Cepheus
Draco
Ursa Major
Ursa Minor


Eastward
Aquila
Cygnu
Lyra

Southward
Libra
Sagittarius
Scorpius



Westward
Corvus
Leo
Virgo

Locate the Big Dipper high overhead. Follow the arc of the handle to 0 magnitude Arcturus (Bootes). Continue the arc to 1st magnitude Spica (Virgo) in the southern sky. From Spica a line upward and to the right passes through 0 magnitude Saturn, 1st magnitude Regulus (Leo) and 1st magnitude Mars.

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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