and Sunset Times for
The period of daylight continues to increase during May. However, the rate of increase slows by the end of the month as the earth approaches the far end of its orbit around the sun. At this point in its orbit the northern hemisphere tilts towards the sun. The sun’s rays strike the earth north of the equator where the radius of the earth is less. The effect is that both morning and evening twilight linger about thirty minutes longer than usual. Civil twilight provides adequate light about one-half hour after sunset. Nautical twilight increases to forty-five minutes during which color and detail fade from the landscape. The final stage, astronomical twilight, also increases to forty-five minutes as the residual light in the western sky fades to blackness. The opposite progression occurs at dawn. (The time of sunrise and sunset assumes a flat horizon. Actual time may vary depending upon the landscape.)
May begins with a waning gibbous moon that does not rise until after midnight. The moon does not return to the evening sky until after the new moon of May 13. A slim waxing crescent moon appears May 15 below Venus. The full moon rises May 27 at 8:48pm. (The time of moonrise and moonset assumes a flat horizon. Actual time may vary depending upon the landscape.)
This month’s meteor showers are washed out by a gibbous moon, but some meteors will still be visible. A bright moon rises in the eastern sky after midnight with the constellations that host the meteor activity. The major meteor event of May is the Eta Aquarid Meteor Shower occurring May 4-7 from the vicinity of Aquarius. Other activity during the first two weeks of the month emanate from Bootes, Hercules, Libra, Scorpius, and Ophiucus. The best time to view meteors is between midnight and 4:00am when the radiant constellation is overhead.
DARK SKY GAUGE
The four stars of the Little Dipper’s basket provide a gauge for measuring the darkness of the night sky. The Little Dipper is much fainter than its companion, the Big Dipper, which is comprised mostly of +2 magnitude stars. The basket of the Little Dipper has one +2 magnitude star and one +3 star. They form the outer edge of the basket. The two inner stars of the basket are +4 and +5 magnitude. If all four stars are visible, then the quality of the night sky is good and about 1700 stars are visible. If only the +2 and +3 magnitude stars are visible, then the night sky quality is less than fair and fewer than 150 stars are visible. Under the darkest skies, most people can see +6 magnitude stars, increasing the number of visible stars to nearly 5000. (See the note for apparent magnitude above.)
LOCAL STAR COUNT
Join Red Rock Astronomers at Old City Park on Sunday, May 16, at 9:00pm 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 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.
Jupiter - The dominant light in the predawn sky this month is Jupiter. It appears on the ecliptic a little south of the celestial equator about one hour before sunrise. (Magnitude -2)
Mars - Look high in the western sky for the bright red disk of Mars between the twin stars of Gemini and the sickle-shaped head of Leo. It appears in the faint constellation Cancer. Each evening Mars advances a little farther east. By April 19 it will have moved eastward through the center of Cancer. Mars is fading in brightness as its orbit recedes from Earth, but it still matches the brightness of Saturn and the first magnitude stars. (Magnitude +0.5)
Mercury - On April 8 Mercury is at its greatest eastern elongation from the sun (farthest point from the sun in its orbit). To see Mercury, first find Venus in the western sky, then use binoculars to scan to the west towards the horizon for Mercury. On April 15 use binoculars to find Mercury to the right of a thin crescent moon right below Venus in the western sky. (Magnitude +0.1)
Saturn - Look for Saturn in the faint constellation Virgo as twilight fades. Its yellow disk appears below Denebola (tail of Leo). Extend a line through Mars, Regulus (Leo’s heart) and Saturn to find Spica (Virgo). (Magnitude +0.5)
Venus - Both Venus and Mercury are in Pisces this month, but the constellation is too faint to be seen so close to the sun. Venus continues to appear low in the western sky so it may not be visible until late in the month when it can be seen between the two star clusters of the Pleiades and the Hyades (the V of Taurus). (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.
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.
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