This month the Moon gives us some exciting displays. Mark your calendars for these exciting events!
See the Moon and the Hyades Star Cluster
April 17 – 19: Right after sunset, look low toward the west-northwest for a view of a slender 2-day old crescent Moon, just 5 percent illuminated. And situated about a half-dozen degrees to its upper right is the steady, dazzling light of the planet Venus. Earth’s “sister planet” gets a little higher each week during April. It remains small and roundish in telescopes this month, but from early April until early September, Venus will be at least 10° above the horizon 45 minutes after sunset (though never very high), and during that period we will see its disk grow and enter its crescent phase.
Also on the 17th, low in the west-northwest sky, right after sundown, will be a slender sliver of a crescent Moon just two days past new phase. This was a sky signal by which the ancients set their calendars. But be sure to make a note the following night, April 18, to look for a very pretty sight, when a slightly wider crescent Moon appears to float near the bottom of the beautiful V-shaped Hyades Star Cluster, marking the face of Taurus, the Bull. Initially in the bright evening twilight, only the Moon will be visible, though once the sky has become completely dark soon after 9 p.m., the Hyades stars should be readily evident with the unaided eye.
Interestingly, the bright orange 1st-magnitude star, Aldebaran at the upper left of the V, is not part of the star cluster at all; it’s just an innocent bystander. The Hyades are 140 light years from us, but Aldebaran is much closer at 67 light years. Yet by happenstance, it helps to furnish along with the members of the Hyades cluster, an almost perfect letter V in our sky.
An Earthshine Opportunity!
Binoculars will greatly enhance the view, not only of the Hyades’ individual stars, but also of the phenomenon known as Earthshine; the waxing crescent Moon appearing as a thin arc of yellowish-white light enclosing a ghostly bluish-gray ball. Actually, for at least several nights, up to nearly a week after the new Moon, sunlight reflected from Earth illuminates the night side of the Moon, making its whole disk visible. Here is one of nature’s beautiful sights and fits the old saying, “the old Moon in the new Moon’s arms.”
The Moon has always been a prime target for telescope observers everywhere and shows amazing detail in even the smallest telescope. Even binoculars will show the mare, or “seas,” mountain ranges, and ringed plains, as well as the great craters, while with a telescope of only 3-inch aperture you can see practically everything as clear as the very best Earth-based photos. Most observers agree that the very best time to view the Moon is in the two- or three-day interval following first quarter. The Moon is then in a good position for evening study with most of its major features visible, while not overly bright (as is the case at full phase) to cause a loss of detail through glare. The best views are along the sharp sunrise line separating darkness from light, called the terminator. Through a telescope, features near the terminator stand out in bold relief; shadows are strong and details are more easily seen.
The Moon’s Greatest Showpiece: Copernicus
April 25: Sometimes you can even notice bright specks of light where high mountains catch the light of the rising Sun before it has reached the plains below. On the evening of April 25th, there will be one prominent crater visible immediately to the right of the terminator. That’s Copernicus, easily the finest example of an impact crater on the visible side of the Moon’s surface, and one of its greatest showpieces. Crowned “the Monarch of the Moon” by T.G. Elger, noted British lunar observer, few would argue against this title.
When an early robotic Lunar Surveyor spacecraft landed near Copernicus in 1966 and photographed in black-and-white the crater’s rim and towering walls, some referred to it as the “Photograph of the Century.” Of course, that title would be quickly forgotten only a few years later when astronauts landed on the lunar surface and photographed some pretty spectacular images of their own – in color.