SkyEye

The Calendar

Mercury attains its largest elongation from the Sun for the year just a day after a particularly close encounter with Jupiter. Earth's first equinox of 2021 occurs this month and later, the morning star vanishes from the dawn sky, only to re-emerge next month low in the west after sunset.

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 Aquarius → Pisces

The solar south pole is most inclined toward the Earth early this month.

Mercury Capricornus → Aquarius

Greatest elongation west of 27.3° occurs on 6 March, the largest elongation of 2021. This is the best morning apparition of Mercury this year for observers in the southern hemisphere and the worst one for those in northern temperate latitudes. The tiny planet begins at magnitude +0.3 and brightens almost an entire magnitude this month. It has two planetary appulses in March, the first with Jupiter on 5 March when the two planets are only 0.3° apart and the second with faint Neptune on 29 March. Mercury also reaches aphelion midmonth, on 14 March.

Venus Aquarius → Pisces → Cetus → Pisces

Planet watchers in the northern hemisphere lost Venus last month and will not see the bright planet again until April when it reappears low in the west. Observers in southern latitudes get a few more days of the morning star at the beginning of the month but the appulse with Neptune on 14 March will be lost in the dawn sky. Venus reaches superior conjunction on 26 March.

Earth and Moon

Earth reaches the first of its two equinoxes on 20 March. The word equinox means 'equal night' so that on this day, the (centre of the) Sun spends an equal amount of time above and below the horizon everywhere on the planet.

Mars Taurus

Mars continues to move slowly across the background skies, fading in brightness as it draws farther from Earth. It is visible in the evening sky and is best viewed from northern latitudes where it doesn't set until after midnight. The waxing crescent Moon comes to within 2° of the red planet on 19 March.

Jupiter Capricornus

Jupiter is visible in the morning sky, now rising well ahead of twilight for southern hemisphere astronomers but still embedded in the glow of the dawn sky for observers farther north. The giant planet is only 0.3° south of Mercury on the fifth day of the month with Jupiter shining at magnitude −2.0 and Mercury much fainter at +0.5. Look for them in the east before sunrise.

Saturn Capricornus

A morning sky object, Saturn is most easily seen from southern latitudes where it rises just after midnight. For observers in the northern hemisphere, the ringed planet is low to the horizon and embedded in morning twilight.

Uranus Aries

Uranus is approaching its April conjunction and is setting earlier every evening. By the end of the month, it disappears below the western horizon around the time of astronomical twilight. Look for the green ice giant early in March when the Moon is below the horizon although it might be interesting to see the waxing crescent Moon just 2.7° away from the faint planet on 17 March. Northern latitudes are favoured.

Neptune Aquarius

Neptune is at conjunction this month and thus unobservable. Planet watchers in the southern hemisphere may be able to glimpse the close approach of Mercury on 29 March just before the onset of morning twilight.