May 2021

Welcome to SkyEye, your guide to this month's celestial events.

The Calendar

Venus is occulted by the Moon on 12 May but it is the Moon itself that is eclipsed two weeks later. Saturn's rings reach their minimum tilt for the year. The two inferior planets are only 0.4° apart in the west late in the month.

The phases of the Moon in May 2021

Date Body Event
3 Saturn west quadrature
Moon last quarter
6 Earth η Aquariid meteor shower
7 Mars occultation of sixth-magnitude star HD 470202
9 Venus ascending node
11 Moon new
Moon farthest apogee of the year
12 Moon, Venus occultation of Venus — visible from the southeastern Pacific
13 Moon ascending node
16 Moon, Mars 1.5° apart
17 Mercury greatest elongation east: 22.0°
18 Mercury maximum declination north
Saturn maxiumum declination north
19 Moon first quarter
20 Saturn minimum ring opening: 16.7°
21 Jupiter west quadrature
23 Saturn stationary point in right ascension: direct → retrograde
26 Moon perigee
Earth, Moon total lunar eclipse
Moon full: Super Moon
Moon descending node
29 Mercury, Venus conjunction: 0.4° apart
30 Mercury stationary point in right ascension: direct → retrograde
Mercury descending node

The Solar System

The word planet is derived from the Greek word for 'wanderer'. Unlike the background stars, planets seem to move around the sky, keeping mostly to a narrow track called the ecliptic, the path of the Sun across the stars. Dwarf planets and small solar-system bodies, including comets, are not so constrained, often moving far above or below the ecliptic.

The position of the Sun and planets at mid-month

Sun AriesTaurus

Mercury AriesTaurus

Mercury continues an excellent evening apparition for northern hemisphere observers. The young crescent Moon passes 2.1° south of the tiny planet on 13 May, just four days before Mercury reaches greatest elongation east (22.0°). It then begins to head back toward the western horizon, passing Venus on 29 May. On the following day, Mercury begins retrograde motion ahead of its inferior conjunction next month. Look for the closest planet to the Sun early in the month when it is at its brightest; it will be only third magnitude by the end of May.

Venus AriesTaurus

This apparition of the evening star lasts until the end of the year. It is a very poor one for observers in northern temperate latitudes, with Venus struggling to reach an altitude of 20°. However, southern observers will eventually see the bright planet appear high above the horizon after sunset. For this month, however, Venus is still fairly low in the west. The very young Moon occults Venus on 12 May. The event begins around 20:30 UT and is visible from the southeastern part of the Pacific Ocean. Mercury speeds past on 29 May, passing just 0.4° south of Venus.

Earth and Moon

Observations of the η Aquariid meteor shower in early May may be slightly hampered by the waning crescent Moon. The farthest lunar apogee of the year occurs on 11 May, followed by a lunar occultation of Venus the next day. However, as the Moon is just past its new phase, it may be too close to the Sun to actually see. Just over nine hours separates perigee and Full Moon, leading to a so-called Super Moon on 26 May. This Super Moon briefly turns reddish as it is totally eclipsed in the Earth's shadow.

Mars TaurusGemini

Mars occults the sixth-magnitude star HD 47020 in a short-lived event beginning around 23:15 UT. The waxing crescent Moon pays a visit to the red planet on 16 May when the two celestial objects are only 1.5° apart in Gemini. Mars is an evening sky object but the Sun is slowly overtaking it and the second-magnitude planet is setting earlier and earlier in the evening. It vanishes below the western horizon just before midnight for observers in northern temperate latitudes but darkness arrives late so seek out Mars as soon as conditions permit. Astronomers in the southern hemisphere lose the planet much earlier in the evening but have around two hours of observing time before Mars sets in the west.

Jupiter Aquarius

The best place to see Jupiter is south of the equator where the giant planet rises during the evening and is high in the sky by the early morning hours. Jupiter remains strictly a morning sky object for planet watchers in northern latitudes and never gains much altitude. West quadrature occurs on 21 May.

Saturn Capricornus

Saturn reaches west quadrature on the third day of the month. The shadows cast by the planet, its rings and moons are all slightly off to one side, leading to some interesting astrophotographic opportunities. The ringed planet reaches its maximum northerly declination on 18 May but it remains a difficult object to see from northern latitudes; southern hemisphere astronomers have much the best views with Saturn rising in the evening. The tilt of Saturn's rings has been closing all year, reaching a minimum value of 16.7° on 20 May before beginning to open up again. Three days later, Saturn enters into retrograde motion.

Uranus Aries

At conjunction on the last day of April, Uranus is lost in the glow of the dawn sky until the end of the month, making its appulse with the nearly New Moon on 10 May impossible to see. Optical aids will be necessary to spot this sixth-magnitude planet and the southern hemisphere is the best place to be for this endeavour.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Astronomers in the southern hemisphere have much the best views of Neptune with the eighth-magnitude planet rising before midnight by the end of the month. Observers farther north will have more of a struggle to see the blue ice giant which doesn't appear in the east until the early morning hours.

The Celestial Sphere

Constellations are patterns of stars in the sky. The International Astronomical Union recognises 88 different constellations. The brightest stars as seen from the Earth are easy to spot but do you know their proper names? With a set of binoculars you can look for fainter objects such as nebulae and galaxies and star clusters or some of the closest stars to the Sun.

Descriptions of the sky for observers in both the northern and southern hemispheres are available for the following times this month. Subtract one hour from your local time if summer (daylight savings) time is in effect.

Local Time Mid-month Northern Hemisphere Equator Southern Hemisphere
1730 hours (1830 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
1930 hours (2030 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
2130 hours (2230 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
2330 hours (0030 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0130 hours (0230 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0330 hours (0430 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0530 hours (0630 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S