SkyEye

The Calendar

Mercury and Venus team up low in the west on 22 May in what is the evening star's last major event this year. Venus will assume the title of morning star late next month. The rings of Saturn close to their minimum tilt for 2020 early in the month. How bright will comet C/2020 F8 (SWAN) get before perihelion passage late in the month?

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 Aries → Taurus

Mercury Aries → Taurus → Gemini

Mercury closes to 1.3° of Uranus on the first day of the month but with both planets so close to the Sun, this event will not be visible. Mercury reaches superior conjunction on 4 May and actually passes behind the disk of the Sun as seen from Earth. The tiny planet reaches its second perihelion of the year on 10 May and has a close encounter with Venus in the west after sunset on 22 May. Mercury begins the month at a bright magnitude −1.7 but dims to +0.2 by June.

Venus Taurus

The evening star is appearing lower in the west every night, on its way to inferior conjunction next month. It enters retrograde motion on 13 May and appears only 0.9° north of Mercury on 22 May when both planets are near the horizon at sunset. Venus disappears in the glow of the twilit skies by the end of the month.

Earth and Moon

The η Aquariids are somewhat spoiled by moonlight early in the month. Look for these meteors in the hours before dawn. Toward the end of the month, on 27 May, the waxing crescent Moon passes 1.7° north of the open star cluster known as Praesepe or the Beehive.

Mars Capricornus → Aquarius

The waning crescent Moon passes less than 3° south of Mars on 15 May. The red planet is best viewed from the southern hemisphere; the ecliptic through Capricornus and Aquarius is relatively low to the southern horizon as seen from northern temperate latitudes so Mars is a more difficult object to observe from those locations. Mars continues to grow brighter and larger in telescopes as it approaches opposition (and closest approach to Earth) in October.

Jupiter Sagittarius

A superior planet enters into retrograde motion before opposition and Jupiter reaches its stationary point on 14 May. This occurs two days after the Last Quarter Moon passes 2.3° south of the planet. Jupiter continues to brighten as the month progresses, from magnitude −2.3 to −2.6. It is easily visible from southern latitudes where it rises in mid-evening. However, for observers in the northern hemisphere, it is still primarily a morning sky object.

Saturn Capricornus

At −19.9° on 6 May, this is as far north in declination as Saturn gets this year. Two days later the rings present their smallest tilt of the year, with an opening angle of 20.5°. Retrograde motion commences on 11 May and on the following day the waning gibbous Moon passes less than 3° south of the ringed planet. Like Jupiter, Saturn is best viewed from the southern hemisphere where it rises before midnight.

Uranus Aries

Uranus was at conjunction near the end of last month and is lost in the glare of the Sun at the beginning of May. It slowly emerges from the morning twilight by the end of the month.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Neptune is difficult to observe from northern temperate latitudes as Aquarius is low to the horizon. Southern hemisphere observers have much better views as the faint planet is high in the darkening skies.