SKY HAPPENINGS

The Sky for October 2015
By Faylene Roth

The Great Square of Pegasus frames a window to the universe where numerous neighboring galaxies can be viewed— tens of millions to hundreds of millions of light years away from us. Beyond them lie quasars (possibly the early phases of galaxies) billions of light years away.

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.

DAYLENGTH
Notice that sunset arrives one to two minutes earlier each day, shortening the length of daylight by 41 minutes in addition to the 30-minute decrease caused by later sunrises. By month’s end the length of daylight will be 10 hours, 36 minutes—still a little more than one hour longer than a winter solstice day.

MOON HAPPENINGS
October 4 – Dark evening skies. A waning last quarter moon rises after midnight.
October 12 – Dark sky period for several days before and after the new moon (6:06pm).
October 20 – Bright evening skies. A waxing first quarter moon sets after midnight.
October 27 – Full moon rises at 6:57pm, becomes full at 6:05am.
(The moon rises later each day—as little as 30 minutes to as much as one hour. Time of moonrise and moonset may also be delayed in mountainous terrain.)
(The moon rises later each day—as little as 30 minutes to as much as one hour. Time of moonrise and moonset may also be delayed in mountainous terrain.)

VISIBLE PLANETS
Jupiter – The second brightest planet is the last of three planets to rise during early morning twilight at the beginning of October. On the morning of October 18 it overtakes Mars when the two planets rise at the same time. Jupiter continues to rise earlier each morning and on the morning of October 26 it overtakes Venus and becomes the first planet to rise for the remainder of the month. (Magnitude -1.6)
Mars -- Look for the red light of Mars trailing behind Venus into the eastern morning sky. It rises on the morning of October 9 with the waning crescent moon and rises within 0.5 ̊ of Jupiter on the mornings of October 17 and 18. By month’s end, Mars is the last of the three visible morning planets to rise, but it will be much closer to Venus. (Magnitude +1.8)
Venus – The pre-twilight eastern sky is pierced with the brilliant light of Venus throughout the month. The planet is approaching its Greatest Western Elongation from the sun which occurs on October 26. Venus rises very early during this period and climbs high into sky before lost in the glare of civil twilight. A waning crescent moon slides past it on the mornings of October 8 and 9. From October 24-27, the three planets converge into a tight triangle which brings them within 1 ̊ of one another. (Magnitude -4.4)

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.

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.