See what's up in the night sky for April 2021, including stargazing events and the moon's phases, in this Space.com gallery courtesy of Starry Night Software.
Thursday, April 1 - Evening Zodiacal Light (after dusk)
If you live in a location where the sky is free of light pollution, you might be able to spot the Zodiacal Light, which will most apparent during the two weeks that precede the new moon on Monday, April 12. Starting at the end of evening twilight you’ll have about half an hour to check the west-northwestern sky for a wedge of faint light extending upwards from the horizon and centered on the ecliptic (i.e., below Mars and the Pleiades Cluster). That glow is sunlight scattered from countless small particles of material in the plane of our solar system.
Friday, April 2 - Mars Passes NGC 1746 (evening)
In the western sky on Friday evening, April 2, the orbital motion of reddish Mars (red path with labeled dates:time) will carry it closely past a large open star cluster designated NGC 1746. That cluster sits between the horns of Taurus, the Bull. The planet will be close enough to the star cluster to see them together in binoculars on the surrounding evenings. At closest approach on Friday, Mars will be positioned just to the upper right (or to the celestial north) of the cluster’s edge, allowing the pair to be viewed at the same time in a backyard telescope (red circle). (Note that your telescope might flip and/or mirror-image the binoculars’ orientation shown here.)
Sunday, April 4 - Third Quarter Moon (at 10:02 GMT)
The moon will officially reach its third quarter phase at 6:02 a.m. EDT (or 1:30 GMT) on Sunday, April 4. At third quarter our natural satellite always rises in the middle of the night and remains visible in the southern sky all morning. The moon will appear half-illuminated, on its western side - towards the pre-dawn sun. Third quarter moons are positioned ahead of the Earth in our trip around the Sun. About 3½ hours later, Earth will occupy that same location in space. The ensuing week of moonless evening skies will be ideal for observing deep sky targets.
Tuesday, April 6 - Old Moon below Saturn (pre-dawn)
Look in the southeastern sky before dawn on Tuesday, April 6 for the waning crescent moon positioned several finger widths to the lower right (or 4.5 degrees to the celestial south) of magnitude 0.75 Saturn. After the moon rises at about 4:15 a.m. local time - about two hours before the sun - you can view the moon and the ringed planet together in binoculars (red circle). Since brighter Jupiter will be shining a short distance to their lower left, the grouping will make a nice photo opportunity when composed with some interesting landscape.
Wednesday, April 7 - Crescent Moon and Jupiter (pre-dawn)
The moon’s visit with the bright morning planets will continue on Wednesday morning, April 7; however, the moon won’t clear the southeastern horizon until after 5 a.m. local time. Once it does, it will sit less than a palm’s width below (or 5 degrees to the celestial south of) very bright, magnitude -2.1 Jupiter – close enough to view them together in binoculars (red circle). Include somewhat dimmer Saturn positioned to their upper right if you capture another nice photo.
Friday, April 9 - Ursa Major Galaxies (all night)
The Big Dipper asterism and its home constellation of Ursa Major are very high in the northern sky in late evening during mid-April - ideal for observing the spectacular galaxies they host in strong binoculars or backyard telescopes on the dark nights this weekend. Draw a line connecting the dipper stars Phecda to Dubhe, and extend it by an amount equal to their separation to arrive at the galaxy named Bode’s Nebula, otherwise known as Messier 81. It’s a magnitude 6.9 spiral galaxy oriented not quite face-on to Earth, making it appear relatively large and bright. A smaller, magnitude 8.4 galaxy named the Cigar or Messier 82 is located half a degree to the north. That allows both galaxies to be viewed together in the eyepiece of a telescope at low magnification (inset). Several other fainter galaxies can be found within a few degrees of Bode’s Nebula.
Saturday, April 10 - Whirlpool and Pinwheel Galaxies (all night)
On evenings during April, the Big Dipper is positioned high in the northeastern sky. Under dark sky conditions two impressive galaxies can be seen in binoculars (red circle) and backyard telescopes by using the bright star Alkaid to locate them. That star marks the tip of the dipper’s handle. The Pinwheel Galaxy, or Messier 101, is a spectacular, large, face-on spiral galaxy positioned a palm’s width to the left (or 5.5 degrees to celestial north) of Alkaid, forming an equilateral triangle with Mizar, the double star at the bend of the handle. This relatively close galaxy (21 million light-years away) is nearly as large as the full moon in the sky (inset). Since the galaxy’s light is spread over such a large area, its overall brightness is low. Aim your binoculars several finger’s widths to the upper right of Alkaid to discover the iconic Whirlpool Galaxy, aka Messier 51. This spiral galaxy’s angular size is smaller, but it will look somewhat brighter in your binoculars and telescope (inset). A secondary galaxy core designated NGC5195 alongside M51 is linked by a bridge of material.
Sunday, April 11 - New Moon (at 10:30 p.m. EDT)
The moon will officially reach its new phase on Sunday, April 11 at 10:30 p.m. EDT or 7:30 p.m. PDT. That translates to 02:30 Greenwich Mean Time (GMT) on Monday, April 12. While new, the moon is travelling between Earth and the sun. Since sunlight can only reach the far side of the moon, and the moon is in the same region of the sky as the sun, the moon becomes completely hidden from view from anywhere on Earth for about a day. After the new moon phase Earth’s celestial night-light will return to shine in the western evening sky.
Tuesday, April 13 - Asteroid Juno Stands Still near Star Mu Oph (Midnight to Dawn)
On Tuesday, April 13, the main belt asteroid designated (3) Juno will cease its regular eastward motion across the distant stars of Ophiuchus and begin a westward retrograde loop that will last until early August. On this night, the faint magnitude 10.8 asteroid will rise just before midnight and then remain visible until the pre-dawn while it crosses the sky less than a finger’s width from the medium-bright star Mu Ophiuchi (μ Oph). Use that star to locate and view the asteroid in your telescope (inset).
Thursday, April 15 - Young Moon and the Bull’s Eye (evening)
In the lower third of the western sky after dusk on Thursday, April 15, the crescent of the young moon will shine just a few finger widths to the right (or celestial north) of the bright, orange star Aldebaran, which marks the southerly eye of Taurus, the Bull. Use binoculars (red circle) to see the V-shaped group of dimmer stars in the Hyades Cluster. Those stars, which form the bull’s face, are sprinkled downwards and to the right (or celestial northwest) of Aldebaran. The bull’s northerly eye is marked by the medium-bright star Ain, or Epsilon Tauri, which will be positioned between Aldebaran and the moon.
Friday, April 16 - Moon Passes Mars (evening)
In the western sky after dusk on Friday, April 16, the waxing crescent moon will be positioned a palm’s width below (or 6 degrees to the celestial west) of the reddish dot of Mars. The following evening, the moon’s orbital motion will shift it a similar distance to Mars’ upper left. In the interim, observers in most of central and eastern Africa, the southern parts of the Middle East, India, Southeast Asia, Indonesia, and most of the Philippines can see the moon pass in front of (or occult) Mars.
Saturday, April 17 - Moon near Messier 35 (late evening)
Once the sky has darkened after sunset on Saturday, April 17, train your binoculars (red circle) on the waxing crescent moon and look for a dense clump of dim stars sitting just to the moon’s lower left (or celestial south). That open star cluster in Gemini is known as Messier 35 or the Shoe-Buckle Cluster. A curved line of bright stars named Tejat, Propus, and 1 Geminorum, which form Castor’s foot, can help you find Messier 35 on a subsequent moonless evening.
Tuesday, April 20 - First Quarter Moon (at 6:59 GMT)
When the moon completes the first quarter of its orbit around Earth at 2:59 a.m. EDT (or 6:59 GMT) on Tuesday, April 20, the relative positions of the Earth, sun, and moon will cause us to see it half-illuminated - on its eastern side. At first quarter, the moon always rises around noon and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings surrounding first quarter are the best for seeing the lunar terrain when it is dramatically lit by low-angled sunlight.
Tuesday, April 20 - Moon Passes the Beehive (overnight)
Several days after passing Messier 35, the waxing gibbous moon will encounter another prominent open star cluster named Messier 44, Praesepe, and the Beehive, in Cancer. In the southwestern sky after dusk on Tuesday, April 20, the moon will be shining several finger widths to the upper left (or 3.5 degrees to the celestial northeast) of that cluster. To better see the “bees”, hide the bright moon just beyond the upper edge of your binoculars’ field of view (red circle). Observers in western Africa and Europe, and the UK will see the moon while it is somewhat closer to Messier 44.
Thursday, April 22 - Lyrids Meteor Shower Peak (pre-dawn)
The annual Lyrids meteor shower, derived from particles dropped by comet C/1861 G1 (Thatcher), runs from April 16 to 30, and will peak in intensity at approximately 12:00 GMT on Thursday, April 22. The Lyrids can produce up to 18 meteors per hour at the peak, with occasional fireballs. The most meteors will appear between midnight and dawn on Thursday, with a reasonable number of meteors on the mornings before and after, too. Lyrids meteors will streak away from a point in the sky (the shower’s radiant) near the bright star Vega, which will be high in the eastern sky before dawn. The bright, waxing gibbous moon will reduce the number of Lyrids in 2021 – but it will set just before 4 a.m. local time – providing about an hour of dark sky before dawn.
Thursday, April 22 - Gibbous Moon near Stationary Vesta (evening)
On Thursday, April 22, the main belt asteroid designated (4) Vesta will complete a westward retrograde loop that it began in January (red path with labeled dates:time). After briefly pausing its motion through the stars of central Leo, Vesta will resume an eastward trajectory. This week look for magnitude 6.65 Vesta sitting less than a finger’s width below (or 0.5 degrees south-southeast of) the star 51 Leonis. On Thursday night only, the bright, waxing gibbous moon will pass less than a palm’s width below Vesta.
Saturday, April 24 - Mercury Moves Past Venus (after sunset)
Immediately after sunset on the evenings surrounding Saturday, April 24, look just above the west-northwestern horizon, where speedy Mercury will be climbing past much brighter Venus. On Saturday, Mercury will be positioned a thumb’s width to Venus’ lower right (or 1.25 degrees to the celestial northwest). On Sunday and Monday Mercury will ascend to Venus’ upper right. The best viewing times will be at about 8 p.m. local time. Ensure that the sun has completely disappeared below the horizon before using binoculars (red circle) or telescopes in your search.
Monday, April 26 - Mars Passes Messier 35 (evening)
In the western sky on the evenings surrounding Monday, April 26, the eastward orbital motion of Mars (red line) will carry the planet closely past the prominent open star cluster Messier 35, also known as the Shoe-Buckle Cluster, in Gemini. Mars will be close enough to Messier 35 to share the field of view of binoculars from April 21 to May 1. They’ll appear together in the eyepiece of a backyard telescope at low magnification (red circle) from Sunday through Tuesday. (Note that your telescope may flip and/or invert the binoculars’ orientation shown here.) Messier 35’s proximity to the ecliptic leads to frequent encounters with the moon and planets.
Monday, April 26 - Full Pink Supermoon (April 27 at 3:31 GMT)
The moon will officially reach its full phase at 3:31 GMT on Tuesday, April 27, which corresponds to 11:31 p.m. EDT on Monday, April 26. April’s full moon, commonly called the Pink Moon, Sprouting Grass Moon, Egg Moon, or Fish Moon, always shines in or near the stars of Virgo and Libra. Full moons always rise in the east as the sun sets, and set in the west at sunrise. When full, the moon’s geology is enhanced - especially the contrast between the bright, ancient, cratered highlands and the darker, younger, smoother maria. This full moon will occur less than 12 hours before perigee, the point in the moon’s orbit when it is closest to Earth, generating large tides worldwide and making this the second of four consecutive supermoons in 2021. Supermoons look about 16% brighter and 7% larger than average (red circle).
Friday, April 30 - The Three Leaps of the Gazelle (all night)
Everyone is familiar with the asterism of the Big Dipper within Ursa Major, the Big Bear. That large constellation spans the zenith after dusk in late April. Three Leaps of the Gazelle is another easily seen, but lesser-known pattern in that constellation. Spaced along a line spanning nearly 30 degrees of the sky, three pairs of medium-bright stars resemble a gazelle’s tracks – or perhaps the toes of the bear. In each pairing, the stars are separated by about a thumb’s width (1.5 degrees). The most westerly stars, Kappa and Iota UMa (or Al Kaprah and Talitha), are found by extending a line drawn diagonally through the Big Dipper’s bowl from Megrez to Merak. The central pair, Mu and Lambda UMa (or Tania Borealis and Australis) sit midway between the bright star Dubhe and Algenubi in Leo. The most easterly duo, Xi and Nu UMa (or Alula Borealis and Australis) are close to a line extended south from Dubhe through Merak. The word Alula arises from Arabic for “first leap”, while Tania means “second”, and Talitha means “three”.