April 2021

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

The Calendar

The Moon eclipses the red planet this month. Our satellite is unlikely to set in time to provide a few hours of darkness in which to observe the Lyrid and π Puppid meteor showers later in April.

The phases of the Moon in April 2021

Date Body Event
2 Moon descending node
Jupiter occultation of sixth-magnitude star 44 Capricorni
4 Moon last quarter
7 1 Ceres conjunction
12 Moon new
13 136199 Eris conjunction
14 Moon apogee
16 Moon ascending node
17 Moon, Mars occultation of Mars — visible from India and southeastern Asia
136108 Haumea opposition
19 Mercury superior conjunction
20 Moon first quarter
22 Earth Lyrid meteor shower
Mercury ascending node
23 Earth π Puppid meteor shower
Venus, Uranus conjunction: 0.2° apart
Mars maxiumum declination north
24 Mercury, Uranus conjunction: 0.7° apart
25 Mercury, Venus conjunction: 1.1° apart
27 Mercury perihelion
Moon full
Moon perigee
29 Moon descending node
30 Uranus conjunction

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 PiscesAries

Mercury AquariusPiscesCetusPiscesAries

Northern observers have had little luck with spotting Mercury during its first morning apparition of 2021 but planet watchers in southern latitudes can still see the tiny planet during the first half of the month as it plummets back toward the eastern horizon. The very old crescent Moon glides past on 11 April but Mercury is soon lost in the solar glare as it undergoes superior conjunction on 19 April. It quickly returns to view in the west after sunset in what is the best evening apparition for northern temperate latitudes. However, the appulses with Uranus (24 April) and Venus (25 April) may come too soon after conjunction to be visible. Mercury reaches its second perihelion this year on 27 April.

Venus PiscesAries

Venus is very low in the west at sunset and will be difficult to spot. Its close proximity to faint Uranus on 23 April will likely go unobserved, along with its conjunction two days later with Mercury. However, a closer appulse with the smallest planet in the solar system awaits next month.

Earth and Moon

The waxing crescent Moon occults the planet Mars on 17 April. Ten days later, Full Moon occurs 12 hours before perigee, leading to unusually high tides.

Mars TaurusGemini

Mars continues to occupy the evening sky, setting around midnight for observers in northern temperate latitudes but vanishing in the early evening hours for those watching from the southern hemisphere. The red planet is occulted by the waxing crescent Moon on 17 April. This event begins around 10:00 UT and is visible from India and southeastern Asia. Mars reaches it most northerly declination of the year on 23 April, the day before it crosses over into Gemini.

Jupiter CapricornusAquarius

The gas giant is a denizen of the morning sky, best viewed from southern latitudes where is it seen to rise around midnight. For astronomers in the northern hemisphere, Jupiter remains close to the horizon, rising after dawn begins. The gas giant occults the sixth-magnitude star 44 Capricorni on the second day of the month, beginning around 08:45 UT and lasting over an hour.

Saturn Capricornus

Saturn now rises before midnight for astronomers in the southern hemisphere but is best seen during the early morning hours when it is high in the sky. Northern observers will struggle to view the first-magnitude object which only appears as the skies brighten.

Uranus Aries

The Moon is making increasingly close flypasts of Uranus this year and on 13 April, the very young Moon comes to within 2.5° of the faint planet. First Venus (on 23 April) and then Mercury (the following day) pay a visit to Uranus but with the green ice giant at conjunction on the last day of the month, neither of these appulses will be visible.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Now past conjunction, faint Neptune occupies the morning sky. It is best viewed from the southern hemisphere where it rises in the east well ahead of the dawn twilight.

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