SKY HAPPENINGS

The Sky for May 2014
By Faylene Roth

Arcturus (Boötes), Spica (Virgo), and Regulus (Leo) form a long acute isosceles triangle stretching horizontally across the overhead sky. Red-hued Mars sits on the lower line about 15° from Spica. On a dark night look for Corvus, Crater, and Hydra low on the southern horizon. The Milky Way hangs below the northern horizon until after midnight when it crests the eastern horizon led by Vega (Lyra) and Deneb (Cygnus).

DAYLENGTH
As Earth approaches the far end of its elliptical orbit, its speed begins to slow. The result is that—even though the period of daylight continues to lengthen—the rate of increase begins to slow. An additional 52 minutes of light is all that May provides, compared to 71 minutes in April. (Although—as the Earth’s orbit presents the tilted face of the northern hemisphere towards the sun—twilight lingers in the northern hemisphere and lengthens the usable period of daylight.) By month’s end daylength is only 12 minutes shy of the longest day of the year.

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
May 7 – First Quarter Moon brightens western sky until after midnight.
May 14 – Full Quarter occurs at 1:16pm and rises at 8:31pm.
May 21– Last Quarter Moon rises a few hours after midnight.
May 28 – New Moon occurs at 12:40pm.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

VISIBLE PLANETS
Jupiter – Jupiter brightens the western sky (in Gemini). It edges closer to Pollux and Castor (Gemini) during the month. Capella (Auriga) is the 1st magnitude star to the north and Procyon (Canis Minor) shines at 1st magnitude to the south. All set around midnight. On the night of May 31 look for a slender crescent moon about 6° below Jupiter. (Magnitude -2.0)

Mars – Look for Mars overhead at midnight in early May. The red planet advances along the ecliptic about 15° ahead of hot, blue Spica (Virgo). On May 12 a waxing gibbous moon traverses the sky fixed between the two. Mars has dimmed significantly (as it recedes from Earth) by the end of May and sets about an hour before morning twilight brightens the eastern sky. (Magnitude -1.0)

Mercury – Mercury reaches perihelion (nearest point to sun) on May 2, so it will be lost in the haze of the sun. On May 25 it reaches its maximum eastern elongation which puts it high in the evening sky and visible through the end of evening twilight. Look for it about 30° below Capella (Auriga). (Magnitude +0.5)

Saturn – The night sky belongs to Saturn this month. Look for it within the center of the four faint stars of Libra (about 50° below Mars). It is visible from dusk until early dawn. The ringed planet reaches opposition (opposite side of Earth from sun) on May 10 and appears very bright at its closest point to Earth for the year. Its rings tilt favorably towards Earth which increases its reflective surface area. On May 14 Saturn appears about 4° below the full moon. (Magnitude +0.1)

Venus – Venus shares the morning sky with Saturn for most of the month, but look for them on opposite horizons. Venus rises on the ENE horizon between faint Pisces and Aries just as astronomical twilight begins to brighten the eastern sky. Be sure to catch Venus and a waning crescent moon rising together within 6°-7° on the mornings of May 25-26. (Magnitude -4.1)

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 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 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.