May 2013 Skywatching


The sun continues to rise farther north of east, appearing higher at noon, and setting farther north of west this month.  The result is that the sun stays in the sky longer.  During May, days lengthen nearly an hour.  Since January 1, daylight lengthens nearly 6 hours by month’s end.


Moon Phase



May 2 Last Quarter 1:39 a.m. 12:33 p.m.
May 10 New Moon 5:59 a.m. 8:49 p.m.
May 17 First Quarter 12:04 p.m. 1:27 a.m. (5/18)
May 24 Full Moon 7:54 p.m. 5:49 a.m. (5/25)
May 31 Last Quarter 1:49 a.m. 11:31 a.m.

Solar Eclipse:   On May 10, observers from Australia and the Central Pacific Ocean region see an annual or ring eclipse.  No part of the eclipse is visible from the contiguous 48 United States.  Observers in Hawaii see partial eclipse with the moon covering about 40% of the sun.

Lunar Eclipse:  At the Full Moon on May 24, the moon dips into the pale outer region of the earth’s shadow between 10:53 p.m. and 11:26 p.m.  For most observers, the change in the moon’s brightness is indistinguishable from a typical full moon.  The Observer’s handbook advises that “such a shallow eclipse is only of academic interest since it will be all by impossible to detect” (p. 132).

Evening Sky

Four planets are visible in the spring evening sky.

In the western sky, Venus enters the evening sky after passing behind the sun last month.

On May 11, shortly after sunset, the moon appears with Venus and Aldebaran in the western sky.  From a view with a clear western horizon, use binoculars to find a thin crescent moon, the star, and Venus.

Mercury joins Venus in the evening sky after the speedy planet passes superior conjunction on May 11, shown in the chart above.  (Click the image to see it larger.) Thereafter, Mercury rapidly moves into the evening sky.

The best planetary grouping of 2013 occurs in bright twilight late in the month.   Find a good observing spot with a clear view of the west-northwest horizon and use binoculars to find the planets:  MercuryVenus, and Jupiter.

The chart above shows the overall movement of the planets from May 24-May 29, 2013.  Rapidly moving Mercury moves upward as compared to the starry background that includes the horns of Taurus,  Zeta Tauri and Elnath.

Here are the events of the six days:

  • May 24:  Brilliant Venus is low in the sky during early twilight.  Mercury is about 1.3 degrees (3 full moon diameters to the upper right of Venus.  Bright Jupiter is nearly 4 degrees to the upper left of Venus.  All should fit into the view of a 7×50 binocular.
  • May 25:  Find Venus in binoculars.  Venus and Mercury are slightly higher than last night, with Mercury slightly over 1.5 degrees to the upper right of Venus.  Jupiter is three degrees to the upper left of Venus.

  • May 26:  Tonight the planets make nearly an equilateral triangle (as shown in the chart above) with Mercury about 2 degrees to the upper right of Venus and Jupiter about 2 degrees to the upper left of Venus. The trio easily fits into a 7×50 binocular field of view.
  • May 27:  Tonight Mercury stands 2.3 degrees above Venus and Jupiter is 1 degree to the left.  The trio continues to fit into a 7×50 binocular field.
  • May 28:  Still appearing in the same 7×50 binocular field, Jupiter is 1 degree to the lower left of Venus and Mercury is nearly 3 degrees above.
  • May 29:  On the final night of the depiction, Venus stands 1.5 degrees above Jupiter, with Mercury three degrees to the upper left of Venus and nearly 5 degrees above Jupiter.  All fit into the field of a 7×50 binocular.

For more about Venus as an evening star, read our posting about it.

Saturn is the fourth planet visible this month, although appearing in a different part of the sky from the planetary trio.  It rises in the east at sunset as it passed opposition during late April.

On May 1, Saturn can be found in the southeastern sky as it darkens.  The diagram above shows Saturn, Spica — the brightest star in Virgo, along with Zubeneschamali and Zubenelgenubi in Libra.  During the month, Saturn retrogrades, moves westward compared to the distant stars.

Late in the month, the moon passes near Saturn.  Just two days before the full moon, Saturn is 5 degrees from the waxing gibbous moon.  The chart above shows them at 9:30 p.m. CDT on May 22.

Mars is not visible this month as it is lost in the sun’s glare.  It was at conjunction last month.  It moves into the morning sky appearing with Jupiter during late July.

The chart above shows the positions of the planets on May 15, 2013.  (Click the image to see it larger.)  From Earth, the sun is nearly between Mars and Earth, making the Red Planet invisible for us.  Jupiter and Venus are in the same direction, yet appearing near the sun for our observations.  Saturn is nearly opposite the sun, making it visible most of the night.

As the sky darkens this month, look for four of the visible planets.

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