Sun
May brings about a strong rebirth of plant and human activity in the mid-northern latitudes. With the brutal winter of 2013-2014, plant emergence is slow at the time of this writing as it is about two weeks behind typical years.
During the month, daylight increases by nearly one hour. The chart above, made from data from data from the US Naval Observatory for Chicago, Illinois , shows the length of daylight throughout the year. The blue region shows the daylight hours for May. By month’s end daylight lasts 15 hours.
Moon
| Phase | Date/Time | Moonrise | Moonset |
| First Quarter | 05/06/14 (10:15 p.m.) | 10:58 a.m. | 12:45 a.m. (05/07) |
| Full Moon | 05/14/14 (2:16 p.m.) | 7:07 p.m. | 5:18 a.m. (05/15) |
| Last Quarter | 05/21/14 (7:59 a.m.) | 12:15 a.m. | 11:44 a.m. |
| New Moon | 05/28/14 (1:40 p.m.) | 4:27 a.m. | 7:13 p.m. |
| Times are Central Daylight Time for Chicago, Illinois, from US Naval Observatory calculations. (For mjb) | |||
Evening Sky
Four planets are visible during the evening hours this month: Mercury, Jupiter, Mars and Saturn.
Mercury
This elusive planet makes its best evening appearance of this year during May. Mercury is always difficult to locate because it appears either in the eastern morning sky before sunrise or western evening sky after sunset. Even as its best as an evening planet, it sets as twilight ends. Mercury is best seen at month’s end.
Mercury and Venus are best seen as morning planets in the autumn or evening planets in the spring. The plane of the solar system, known as the ecliptic, makes steep angles with the horizon during spring evenings and autumn mornings.
During May, Mercury reaches its greatest angular separation from the sun, known as greatest elongation east. The planet is east of the sun, making it visible in the western sky after sunset.
Mercury’s orbit is tilted about 3 degrees compared to the ecliptic. With Mercury reaching its greatest elongation and its greatest angle with the ecliptic, this coincidence provides the planet’s best evening appearance this year.
The chart above shows the ecliptic and Mercury’s orbit as the planet reaches its greatest angular separation from the sun.
Even with favorable orbital factors, Mercury is difficult to see. On the chart above, Mercury appears low in the western sky, just 30 minutes after sunset. Bright Jupiter is nearly 23 degrees to the upper left of Mercury.
On May 30, a thin waxing crescent moon appears about 8 degrees to the left of Mercury.
To locate Mercury, look with binoculars; after finding the planet, locate it without optical aid.
Jupiter
Jupiter is the bright “star” high in the western sky during the early evening hours. It is in front of the stars of Gemini, with its bright stars Castor and Pollux.
This giant planet is moving eastward compared to its starry background. The chart above shows the planet’s motion during the month, indicating Jupiter’s position on May 1, 10, 20 and 30. Weekly observations of the planet will reveal the motion of the planet.
Early in the month, the moon moves through the region sky near Jupiter. The best evening is May 4, when Jupiter and the moon are about 9 degrees apart.
Mars
Meanwhile Mars is well up in the southeastern sky at sunset. It continues to move westward (retrograde) for most of the month, until May 21st. It then resumes its eastward motion compared to the stars. (See our posting about the retrograde motion of Mars.)
Saturn
Saturn reaches opposition on May 10 and enters the evening sky at sunset. The planet is south at midnight, and it sets at sunrise.
At the beginning of the month, Mars and Saturn are 40 degrees apart.
To distinguish the planets from the stars, Jupiter is the brightest starlike object in the western sky. It is twice the brightness of Mars. Mars is over three times brighter than Saturn, making Jupiter nearly 7 times brighter than Saturn.
Just before mid-month, the moon moves through the region of the sky with Mars and Saturn. On May 10, the moon is 6 degrees to the right of Mars. The next evening, the Moon is 9 degrees to the lower left of Mars. On May 13, Saturn is 5 degrees to the lower left of the Moon. On May 14, the pair is 9 degrees apart.
Morning Sky
Venus remains the brilliant “Morning Star” in the eastern sky before sunrise. See our posting about Venus’ morning appearance. Venus is low in the sky for the reasons explained with Mercury’s favorable view this month.
The angle of the ecliptic is low, on spring mornings, and the planet is beneath the solar system plane. The result is that Venus appears low in the sky.
On May 25, the waning crescent moon appears 2 degrees from Venus.
Visible Solar System
Happy sky watching!