and Sunset Times for
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 in three stages. Civil twilight lasts about one-half hour after sunset. Nautical twilight continues for another 30-45 minutes with color and shapes still apparent. Astronomical twilight begins when color and detail disappear from the surrounding view. The lingering summer twilight continues to push back the best time for stargazing until after 10:00 pm until midmonth. By the end of the month, the skies are truly dark by 9:30 pm. The reverse progression applies to dawn.
(The time of sunrise and sunset assumes a flat horizon. Actual time may vary depending upon the landscape.)
August 2 – Last Quarter Moon rises at 11:56 pm
August 9 – New Moon occurs at 9:08 pm
August 16 – First Quarter Moon sets at 12:03 am
August 24 – Full Moon rises at 7:47 pm
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)
Look for the moon above the Pleiades in the early morning twilight of August 4. It joins the conjunction of Venus, Mars, and Saturn on the evenings of August 13 and 14 . On August 17 it appears one degree above Antares (Scorpius) in the evening sky. The full moon of August 24 is smaller than usual because it is at its greatest distance from Earth for the year.
Astronomers use two types of magnitude scales to measure the brightness of stars. Absolute magnitude reflects actual differences in size and the intensity of a star’s light as if all stars were the same distance from Earth. Apparent magnitude, more useful to stargazers, ranks a star’s brightness based on what we actually see from Earth. A small star near Earth appears brighter than a large more distant star. The current scale for apparent magnitude extends from -26.8 to accommodate the brightness of the sun to +27 to accommodate the faintest objects seen with the largest telescopes. A full moon has an apparent magnitude of -12.6; Venus varies from -3.9 to -4.7; Sirius, the brightest of all stars, is -1.6; the brighter stars like Rigel, Capella, and Vega are designated magnitude 0. Notice that the brightest objects have lower numbers. The faintest stars visible with the unaided eye is 6th magnitude for most people.
Under dark sky conditions some people will see 7th and 8th magnitude stars. Go to a dark sky location on a moonless night to test your vision and to determine the quality of your dark skies. Find the constellation Cygnus. Its brightest star, Deneb, is part of the Summer Triangle. Deneb, (tail of the swan) is a 1st magnitude star. The star to its right (center of the wings) is a 2nd magnitude star. Use the hand-distance scale (in italics below) to find the following stars. About 15 degrees to the right of the central wing star is Albireo (head of the swan). It is a 3rd magnitude star. Ten degrees to the left is a 4th magnitude star. Move two degrees to the right to find a 5th magnitude star. Another three degrees to the right reveals a 6th magnitude star. With excellent eyesight and the darkest of skies, an even fainter 7th magnitude stars appears a little farther right.
August nights promise meteors from the south, east, and north; but one of the best meteor event of the year spreads across the northeastern sky from Perseus. The Perseid Meteor Shower peaks August 12/13. A faint waxing crescent moon sets before midnight leaving dark skies for most of the night. Viewing will be good August 11-14. Meteor activity extends through the first three weeks of August and can produce 60 meteors per hour at its peak. Best viewing times for most meteor showers is when the radiant constellation is directly overhead and improves as dawn approaches.
LOCAL STAR COUNT
Join Red Rock Astronomers at Old City Park on Sunday, August 8, at 9:15 pm 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 fist with the thumb extended at a right angle equals 15 degrees. The hand stretched from thumb to little finger approximates 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.
Jupiter - The second brightest planet of our solar system claims the night sky before midnight. It rises almost due east with Aquarius about the same time the early evening planets are setting. Look for it high in the western sky at dawn. (Magnitude -2.7)
Mars - The red orb of Mars dims slightly as it recedes from Earth. Be sure to follow its do-si-do with Saturn and Venus as the three planets switch positions during the month. After August 6, Mars appears east of Saturn. Mars is in Virgo. (Magnitude +1.5)
Saturn - Mars and Saturn slide past one another during the first week of August. On August 5 the two planets set within one minute of one another. Saturn’s position against the background stars shifts eastward through Virgo. (Magnitude +0.3)
Venus - It’s hard to miss Venus’s brilliance in the evening sky. On August 5 it forms a triangle with Mars and Saturn. By August 12 the three planets have reconfigured with Saturn now to the west of the others. Venus moves towards the southwestern horizon during the last half of the month approaching Mars with Saturn positioned below. All are in Virgo . (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.
CONSTELLATIONS this MONTH
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