SkyEye

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 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.

Sun Pisces → Aries

Mercury Aquarius → Pisces → Cetus → Pisces → Aries

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 Pisces → Aries

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 Taurus → Gemini

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 Capricornus → Aquarius

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.