SKY HAPPENINGS

The Sky for September 2014
By Faylene Roth

The Summer Triangle formed by 1st magnitude stars in Lyra, Cygnus, and Aquila dominates the overhead sky. To the northeast dense clouds of our Milky Way reach out towards the edge of our galaxy through Perseus and beyond. To the southwest ever denser clouds lead toward the galaxy’s center near Sagittarius, low on the southwestern horizon. Black areas that create a marbled effect within the Milky Way are clouds of star dust and gas too dense for light to penetrate. The region below Boötes and Ursa Major directs our view towards the top (relative to the northern hemisphere) of our flattened spiral galaxy. The outline of the Great Square of Pegasus frames a window through the bottom of our galaxy.

Twilight extends the period of daylight in three stages at each end of the day. Morning twilight begins with astronomical twilight—about 1-1/2 hours (nearly 2 during summer months) before sunrise—as the eastern horizon brightens. Nautical twilight continues—as the overhead sky turns blue and color returns to the surrounding landscape—for another 30-40 minutes. The final stage—civil twilight—provides adequate light for most outdoor activities for the half hour before the sun crests the horizon. The opposite progression occurs after sunset.

MOON HAPPENINGS
September 2 – First quarter moon brightens evening sky until midnight.
September 8– Full moon occurs at 7:38pm, rises at 7:21pm, and brightens the sky throughout the night.
September 15– Dark evening skies until last quarter moon rises after midnight.
September 23/24– New moon at midnight darkens night skies for several days before and after.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

AUTUMNAL EQUINOX
Summer relinquishes its hold on the northern hemisphere at 8:29pm, September 22. At that moment the sun’s apparent pathway across the sky passes the equator and moves into the southern hemisphere. In celestial terms, the autumnal equinox marks the moment when the ecliptic crosses the celestial equator. This point is in Virgo. The autumnal equinox provides good conditions for viewing the zodiacal light. Look for a white cone of light due east above the horizon about one-half hour before astronomical twilight brightens the morning sky. The zodiacal light is caused by beams of light shooting straight up from the sun (through dust motes circling within the solar system) before it crests the horizon.

VISIBLE PLANETS
Jupiter – Our two brightest planets grace the morning sky this month. Look for Jupiter in Cancer in the pre-dawn northeastern sky about an hour before Venus rises. Jupiter rises several minutes earlier each day. By month’s end look for it around 3:00am. (Magnitude -1.8)

Mars – Both Mars and Saturn have dropped low on the western horizon. Distinguish Mars by its redness. After the first few days of the month, it remains in the night sky after Saturn sets. Mars rises a little earlier each evening which puts it higher in the sky each night. It moves from Libra to Scorpius (September 13) and then Ophiucus (September 26). (Magnitude +0.7)

Saturn – Saturn and Mars, both in Libra, switch positions on the western horizon during the first few evenings of the month. Saturn continues to set earlier each day. By month’s end it is gone within one-half hour of astronomical twilight’s final glow. Saturn’s yellow light easily contrasts the redness of Mars. From September 27-29 a waxing crescent moon passes by Saturn then Mars. (Magnitude +1.4)

Venus – Saturn and Mars, both in Libra, switch positions on the western horizon during the first few evenings of the month. Saturn continues to set earlier each day. By month’s end it is gone within one-half hour of astronomical twilight’s final glow. Saturn’s yellow light easily contrasts the redness of Mars. From September 27-29 a waxing crescent moon passes by Saturn then Mars. (Magnitude +1.4)

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.

Hold your hand at arm’s length to measure apparent distances in the sky. The width of the little finger approximates1.5̊. 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.

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

Note: Hold your hand at arm’s length to measure apparent distances in the sky. The width of the little finger approximates 1.5̊. Middle, ring, and little finger touching represent about 5̊. The width of a fist is about 10̊. The fist with the thumb extended at a right angle equals 15̊. The hand stretched from thumb to little finger approximates 20̊-25̊. The diameter of both the full moon and the sun spans only 0.5̊. Adjust for the size of your hand.