It’s a busy week, with the Crescent Moon waxing to its second first Quarter Moon of April. As well, look for the Lunar X and Venus at maximum brightness.
Monday, April 27 evening – Crescent Moon near Messier 35
In the western sky on the evening of Monday, April 27, the waxing Crescent Moon will pass close to three medium-bright stars named Tejat, Propus, and 1 Geminorum, which form the feet of Castor, the more westerly twin of Gemini. At the same time, your binoculars might reveal a tight cluster of stars sitting less than two finger widths to the right (or 1.75 degrees to the celestial northwest) of the Moon. That’s an open star cluster known as Messier 35, M35, or more appropriately, the Shoe-Buckle Cluster. The cluster and the Moon will be close enough to fit together in the field of view of binoculars (red circle) — but the cluster will be more apparent if you keep the bright Moon just outside your binoculars’ field of view.
Monday, April 27 evening – Venus at maximum brightness
On Monday, April 28, the evening planet Venus will achieve its “greatest illuminated extent” for the current lengthy evening apparition. That terminology describes the optimum combination of the approaching planet’s apparent disk size (38 arc-seconds) and its illuminated phase. That evening, Venus will shine at a spectacular magnitude —4.73. Its 27-per-cent illuminated crescent phase (inset) will be apparent in any telescope or spotting scope, good binoculars — or even to very sharp, unaided eyes.
Wednesday, April 29 around 9:45 p.m. EDT – Lunar X
Several times a year, for a few hours near its first quarter phase, a feature on the Moon called the Lunar X becomes visible in strong binoculars and backyard telescopes.
When the rims of the craters Purbach, la Caille, and Blanchinus are illuminated from a particular angle of sunlight, they form a small, but very obvious X-shape. The phenomenon called is pareidolia — the tendency of the human mind to see familiar objects when looking at random patterns.
The Lunar X is located near the terminator, about one third of the way up from the southern pole of the Moon (at 2° East, 24° South). The prominent round crater Werner sits to its lower right.
On Wednesday, April 29, the Lunar X is predicted to peak in intensity at 9:44 p.m. EDT (or 01:44 GMT on Thursday, April 30) — but the phenomenon will be visible for approximately two hours on either side of that time. This event should be visible wherever the Moon is shining in a dark sky during that time window. Simply adjust for your difference from the Eastern Time zone. For the Americas, the Moon will be positioned in the southwestern evening sky.
Thursday, April 30 wee hours – Moon near the Beehive again
Low in the northwestern sky in the wee hours of Thursday, April 30 to see the waxing half-illuminated Moon positioned a palm’s width to the lower right (or six degrees to the celestial west) of the large open star cluster known as the Beehive or Messier 44 in the constellation of Cancer, the Crab. This is the Moon’s second such meeting in April. The Moon passes close to, or through, this cluster frequently because the Beehive is located only one degree north of the ecliptic (green line).
Thursday, April 30 at 20:38 GMT – Second first Quarter Moon of April
When a lunar phase occurs on the first day of a calendar month, it can repeat at month-end – so tonight brings a first quarter phase for the second time this April.
When the Moon reaches its first quarter phase, the relative positions of the Earth, Sun and Moon cause us to see the Moon half illuminated on the western (right-hand) side. Sunlight striking the Moon at a shallow angle produces spectacularly illuminated landscapes along the pole-to-pole terminator that separates the lit and dark hemispheres.
First Quarter Moons rise at noon and set at midnight, so they are visible starting in the afternoon hours. And another bit of trivia: the term first quarter refers not to the Moon’s appearance, but the fact that our natural satellite has now completed one quarter of its orbit around Earth, counting from the last New Moon.
Sunday, May 3 from 6:35 to 10:00 GMT – Callisto’s shadow and the Great Red Spot on Jupiter
From time to time, the small, round, black shadows cast by one or more of Jupiter’s four Galilean moons can be seen in amateur telescopes as they cross the disk of the giant planet. Every second or third day, we can see the Great Red Spot on the planet for several hours. On Sunday, May 3 from 6:35 to 10:00 GMT (or 2:25 to 6 a.m. EDT) observers in the Americas with good quality telescopes can watch Callisto’s shadow cross Jupiter, accompanied by the Great Red Spot.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.