The Night Sky This Month: April 2016

Crescent Moon with Earthshine
Crescent Moon with Earthshine by Alan Dyer [amazingsky.com]

Constellations

The winter constellations are beginning to gradually move off the western horizon to be replaced by their spring counterparts. This month, Orion, Canis Major, Gemini, Taurus and Auriga now linger in the sky for less than an hour after sunset, while rising to prominence in the night sky is the Spring Triangle, marked by the main stars in three separate constellations, namely Regulus in Leo, Spica in Virgo, and Arcturus in Bootes. The pointer stars of the “Big Dipper” are an excellent way to locate these spring constellations, using the mnemonic “arc to Arcturus and spike to Spica”.

Meteor Showers

The Lyrids shower is associated with Thatcher’s Comet, and it will be active from April 16 to 25, whilst peaking around midnight to two hours or so before dawn, on April 21/22. During peaks the maximum rate is about 10 meteors per hour, with the radiant being close to the bright star Vega in the constellation Lyra. However, this year the shower may be difficult to observe since it coincides with a full Moon, but stray meteors may be seen for several days on either side of the peak date.

The Moon

The Moon will be at perigee (closest point to Earth) on the 7th of April, when it will be just 35,7163 km away, and at perigee (furthest point from Earth) on the 21st, when it will be 40,6350 km away. Below are the Moon phases for April.

New Moon: April 7th
First Quarter: April 14th
Full Moon: April 22nd
Last Quarter: April 30th

April also offers excellent opportunities to see Earthshine, or light reflected off the Earth to illuminate parts of the Moon. This occurs during the waning crescent Moon in the first five days of April, and again from the 8th to the 13th of the month during the waxing crescent Moon.

The Planets

Spring TriangleJupiter

Jupiter is visible in Leo almost throughout the whole night during the first half of the month, after which it sets at around 04:00. On morning of the 18th, the waxing gibbous moon will pass a few degrees to the southward of Jupiter, and being the two brightest objects during the month, the pair will form an interesting conjunction.

Mercury

On the 18th of the month, Mercury reaches maximum elongation at 20 degrees east of the Sun. At this time, it will set about two hours after sunset, meaning that for most of the month, the planet should be visible low on the west-north-western horizon as twilight deepens. Toward the month’s end, Mercury will become invisible as it approaches inferior conjunction with the Sun.

Venus

Venus spends this month very close to the Sun, and is thus not a naked-eye object during the whole of April. Venus will be partially occulted by a thin, waning crescent moon (one day before New Moon), during daylight hours between 07:00 and 08:00 on the 6th of the month. However, this is a potentially dangerous event to observe, since the Moon-Venus pair will be only about 16 degrees from the Sun. We do not recommend that anyone attempts to view this grazing occultation without specialized equipment, such as appropriate solar filters on optical equipment.

Mars

Mars is now a conspicuous morning object as it approaches opposition in May, rising as it does before astronomical midnight during April. Look for Mars in the south-east during the middle of the month, when both Mars and the star Antares rise above the horizon to their highest possible culminations, but with Mars being the brighter of the two.

During this time, the planet Saturn joins the pair to form a triangle, but on the 25th of the month, the gibbous waning moon joins the grouping to form a right-angled triangle at about 03:00 in the morning with Mars and Saturn, with Mars at the apex of the right-angle.

Saturn

Saturn is a morning object during April, lying eastward of Mars, but sadly, never more than 16 degrees above the southern horizon. As April starts, Saturn will rise around midnight, rising progressively earlier as the month wears on, rising just after 22:00 at the month’s end. On the morning of the 26th, the waning Moon will be separated from the ringed planet by about 4 degrees towards its upper left, when Mars joins the grouping to form a linear arrangement about 16 degrees above the southern horizon. From left to right, the alignment will be the Moon, Saturn, and then Venus.