SkyEye

The Calendar

Observers in northern temperate latitudes get their best evening views of Mercury this month. A rare hybrid solar eclipse occurs on 20 April, with the Sun undergoing both an annular and a total eclipse during different parts of the track of the Moon's shadow. The Lyrid meteor shower takes place shortly thereafter, with no moonlight to interfere.

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 Pisces → Aries

Mercury's excellent evening apparition for northern latitudes continues this month, with the tiny planet continuing to climb higher above the western horizon until around mid-month when it then starts to lose altitude. Greatest elongation east (19.5°) occurs on 11 April. On 21 April the waxing crescent is found just under 2° south of the planet; on the same day Mercury enters into retrograde motion. Mercury aficionados should seek it out early in the month, when it's at its highest and brightest in the evening twilight; it will be sixth-magnitude by the end of April.

Venus Aries → Taurus

Venus continues to rule the western skies at sunset. It is slowly brightening, ending the month at magnitude −4.1, and appears a little higher above the horizon every night. On 11 April, it is less than 3° south of the open cluster M45, the Pleiades. Perihelion takes place on 17 April and the waxing crescent Moon pays a visit on 23 April when the two bodies are just 1.3° apart.

Earth and Moon

A rare hybrid solar eclipse takes place on 20 April. The waxing crescent Moon should not spoil observations of the Lyrid and π Puppid meteor showers a few days later. There are no visible lunar occultations of planets this month (the nearly New Moon occults Jupiter during daylight on 19 April) but the Moon does pass close by several bright stars: Antares on 10 April, the Pleiades on 22 April and finally Pollux on 26 April. The closest apogee of the year takes place two days later.

Mars Gemini

Mars continues to fade in the evening sky, dimming from magnitude +1.0 to +1.3 over the course of the month. In a telescope, it appears slightly gibbous in shape and gets a little smaller each night as Earth leaves it behind. The red planet approaches two named stars in Gemini this month, passing 0.2° north of third-magnitude Mebsuta (ε Geminorum, a G-type supergiant star) on 14 April and a rather more distant 1.9° north of fourth-magnitude Wasat (δ Geminorum, an F-type subgiant star) on the last day of the month. In between these two events, the waxing crescent Moon makes a distant 3.2° pass by the rocky world.

Jupiter Pisces

The largest planet in the solar system undergoes conjunction on 11 April and is largely lost to view this month. It reappears low in the east before sunrise for southern hemisphere observers by the end of the month.

Saturn Aquarius

Visible only in the morning sky, Saturn is best observed from southern latitudes where the ecliptic arches high overhead. The waning crescent Moon makes a distant pass south of the ringed planet on 16 April, approaching no closer than 3.5°.

Uranus Aries

A very young crescent Moon passes 1.7° north of Uranus on 21 April. However, sixth-magnitude object sets during evening twilight and will be difficult to spot; conjunction occurs next month.

Neptune Pisces

Following conjunction last month, Neptune is now a morning sky object. It remains mired in morning twilight as seen from northern latitudes; the southern hemisphere is the place to be to observe the eighth-magnitude planet this month. The waning crescent Moon is found 2.3° south of Neptune on 17 April.