SKY HAPPENINGS

The Sky for April 2015
By Faylene Roth

On April 5, 1st magnitude blue-white Spica (Virgo) rises in the eastern sky a few degrees below the waning full moon. Look northward about 35 ̊ for 0- magnitude red star Arcturus (Boötes). During the new moon period check the amount of light pollution in the night sky by tracing a line from 1st magnitude blue star Regulus (Leo) to Jupiter. Another 7-8 ̊ along this line leads to the faint Beehive Cluster—visible with the naked eye under truly dark skies. Give your eyes at least 20-30 minutes to adapt to the darkness before trying this.

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
When the sun rises on April 17 at 6:40am, we will have regained the hour of morning light lost to daylight saving time last month. The rapid increase in the period of daylight continues to advance at a rate of about 2-1/2 minutes per day. By month’s end, the period of daylight will have increased by 71 minutes.
Twilight extends the period of daylight in three stages at each end of the day. Morning twilight begins with astronomical twilight as the eastern horizon brightens —about 1-1/2 hours (nearly 2 during summer months) before sunrise when the sun is 18 ̊ below the horizon. Nautical twilight takes over for another 30-40 minutes—as the sun passes 12 ̊ below the horizon and the overhead sky turns blue and color returns to the surrounding landscape—. The final stage—civil twilight—begins when the sun ascends to 6 ̊ below the horizon and provides adequate light for most outdoor activities for the half hour before the sun crests the horizon. The opposite progression occurs after sunset.
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MOON HAPPENINGS
April 4 – Full moon (6:05am) rises at 8:11pm.
April 12 – Dark evening skies until after midnight when the waning last quarter moon rises.
April 18 – Dark sky period for several days before and after the new moon (12:46pm).
April 25 – Waxing first quarter moon brightens evening skies until after midnight.
(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.)

LUNAR ECLIPSE
Rise early on the morning of April 4 to watch the lunar eclipse. The previous night’s nearly full moon transforms into a sienna moon as the Earth passes between sun and moon and casts its full shadow across the moon’s face. The Earth’s shadow appears dark as it passes across the moon’s surface. Once the moon is totally enshrouded, filtered sunlight passing through the Earth’s atmosphere bends long red wavelengths of light back towards the moon. The moon’s color can vary from coppery tones to deep reds depending upon atmospheric conditions—dust, smoke, etc. Most of the eclipse occurs during morning twilight. The following timetable details how the eclipse phases intersperse with the stages of twilight followed by sunrise and moonrise. Thanks to the Clark Planetarium in Salt Lake City for the eclipse timing in Utah.

Partial phase begins at 4:16am - Astronomical twilight begins at 5:27am
Total phase begins at 5:58am - Nautical twilight begins at 6:00am
Greatest eclipse occurs at 6:01am
Totality ends at 6:03am - Civil twilight begins at 6:32am - Sun rises at 6:59am - Moon sets at 7:06am
Partial phase ends at 7:45am

ZODIACAL LIGHT
Use Venus as a beacon to find the zodiacal light. It’s a cone-shaped beam of light shooting almost straight up from the western horizon in the direction of Venus. Look for it after astronomical twilight darkens the night sky. Once the sun has dropped about 24 ̊ below the horizon, the zodiacal light is produced as the sun’s rays pass through and reflect off dust particles in the inner solar system.

MAJOR METEOR EVENTS
No major meteor showers occur in March, but fireballs and scattered meteor activity are not uncommon. Look for slow-moving meteors during the dark sky new moon period from radiants near the circumpolar constellation Camelopardalis (Giraffe) and overhead from Gemini (Twins).

VISIBLE PLANETS
Jupiter -- To find Jupiter in the evening sky face south and look overhead for the brightest point of light. Jupiter sits on the ecliptic—west of 1st magnitude Regulus (Leo) and east of faint Cancer. No longer a feature of the morning sky, it dips below the western horizon about 90 minutes before morning twilight begins. (Magnitude -2.2)
Saturn – Saturn now rises before midnight and lingers on the western horizon through morning twilight. On April 8 it rises about 10 minutes before and within 2 ̊ of a waning full moon. Look for it between 11pm and midnight, depending upon your elevation and surrounding landscape. (Magnitude +1.1)
Venus – Venus dominates the star-studded western horizon until almost midnight. Look for it north of 1st magnitude red star Aldebaran (Taurus). Venus is currently on the far side of the sun with about 75% of its face lit. It reaches perihelion (closest point to sun) on April 18. (Magnitude -4.1)

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.