What's Up in the Night Sky

May 2016 - Vol. 20, No. 5

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

As May brings the lengthening days, the hours of nightly observation decrease as well, it is always with a bit of sadness that we say good-bye to the Winter and Spring constellations, Gemini, Leo, and Virgo. The early evening presence of Arcturus, the second brightest star in the northern sky, reminds us that the bright star clouds of the Milky Way will soon be brightening up those dark evenings when the Moon is small enough to allow us to truly enjoy those galactic treasures. As the evening turns to morning, the bright stars of the summer triangle follow until just before sunrise, the Milky Way is at the zenith, high overhead. Long twilight hours come to the northern hemisphere.

MERCURY is well placed in the morning sky this month appearing best for southern observers in the second half of the month. A transit of Mercury will be visible on May 9 with the aid of a telescope, see the monthly topic for more details. VENUS is too close to the Sun to be observed this month. MARS reaches opposition on May 22 and will be visible all night. JUPITER still in Leo, will be in conjunction with the moon on May 15. SATURN, located in Ophiuchus, rises in the late evening this month. The outer planet NEPTUNE still in the constellation of Aquarius rises in the morning sky.

Review how to determine Angular Measurement.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time. Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times or check with the U.S. Naval observatory. Unfortunately some of these events may occur during daylight hours in your area.

DATE	EVENT
05	Eta Aquarid meteor shower peak, up to 60 per hour may be seen at the zenith from a dark site. Best observing is after midnight, watch for meteors on Thursday morning.
06	Moon at perigee, expect large tides in coastal areas.
09	Transit of Mercury will be widely visible over the Earth including the Americas, Atlantic and Pacific Oceans, Europe, Africa and much of Asia. It cannot be seen from eastern Asia, Japan, Indonesia or Australia. Important! To observe the transit, please take all precautions when observing the Sun! A detailed article on Mercury transits is available in the monthly topic area of the almanac.
14	Aldebaran 0.5 deg S. of the Moon occultation from southern Europe, northern and northeast Africa, Middle East, and most of southeast Asia. Spring Astronomy Day celebration for 2016.
15	Jupiter 2 deg N. of Moon, a nice conjunction in the evening sky.
18	Moon at apogee.
19	Mercury at aphelion, furthest distance from the Sun, 0.4667 AU or 43,382,475 miles.
21	The full Moon this month is considered a blue moon as the third Full Moon this season with four new moons in total for the northern hemisphere Spring. This year there are 13 full moons, an event that happens in only 7 years out of 19 years. Because this special moon does not have a traditional name, it is called the Blue Moon. (A bit of an oddity since the second full moon in any given moon is also called a "blue" moon.)
22	Mars at opposition. This year's opposition occurs while Mars is in the constellation of Scorpius. The north pole of the planet is shrinking and will be pointed toward Earth. The shining red planet should be at -2.1 magnitude and rival Jupiter for brightness.
23	Vesta in conjunction with Sun.
30	Mars closest approach to Earth, for this opposition, the planet will be a mere 46.8 million miles at 22h UT.

Lunar Almanac for May 2016

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 06	Deep Space Objects
	1st. Qtr 13	Planets & Moon
	Full 21	Moon
	Last Qtr 29	Deep Space & Planets

Topic of the month: Transit of Mercury

Transits of Mercury occur when the inner planet Mercury crosses the plane of Earth's orbit and appears as a tiny dot crossing the disk of the Sun. These transits occur on a regular basis, although they are considered a rare event with 13 or 14 transits per century. Because Mercury is closer to the Sun than Venus, transits of Mercury occur more often, and will occur in the month of May or November, in this century. The last transit of Mercury occurred in November of 2006. During transits in May, the angular diameter of the planet crossing the Sun is about 12".

Because of the small size of Mercury and its distance from the Earth, a telescope will be necessary to view the transit. Any attempt to view the event must be made with the proper filters and observers must be aware that viewing the Sun without a proper protection can result in damage to the eye. Unfortunately, the disk of Mercury is too small to use the pinhole technique on the Sun. During transits in May, the fleet-footed planet is at the aphelion point in its orbit, it is crossing Earth's orbit at its descending node, appearing to move southward across the ecliptic.

The precise time of ingress or first contact is 11 h 12m 18s UT when Mercury first "touches" the solar disk. At this time, the planet will appear as a notch against the Sun's limb. The entire transit will be visible from North and South America, the Atlantic and Pacific Oceans, Europe, Africa, and most of Asia, although observers in Australia and Japan are not so lucky. An image of Mercury transiting the Sun in May of 2003 was published on APOD, the astronomy picture of the day. The transit this year will cross the Sun's disk for 7 hours and 30 minutes from any location where the transit can be seen in its entirety, from first contact to fourth contact known as egress. The planet crosses the disk from the northeast and travels toward the southwest.

For more information on the transit of Mercury in 2016, go to Fred Espenak's page at EclipseWise.com: 2016 Transit of Mercury. Other sources can be found on the web, including The Naked Eye Planets by Martin J. Powell and site's page on the Transit of Mercury includes an animation showing where the Sun is located above the Earth while the planet crosses the the Solar disk. Many other pages describing the transit and giving more information than is available here at the Stargate can be found by searching the internet. The Association of Lunar and Planetary Observers (ALPO) collects observations and will gladly accept observations, just be sure to check out the instructions for submitting your observations and provide all the details that are requested as outlined by the ALPO Mercury/Venus transit coordinator in this reprint from the Strolling Astronomer.

--See You Under the Stars!
Astra for Astra's Almanac

The image of the transit of Mercury was developed by Fred Espenak and is imported to this almanac as a linked image from the Eclipse Wise web site, click on the image to go to the original posting at the The 2016 Transit of Mercury at EclipseWise.com to get more information on this rare event.