Non-Profit Internet Source for News, Events, History, & Culture of Northern Frederick & Carroll County Md./Southern Adams County Pa.

 

The Night Sky of April

Dr. Wayne Wooten
Professor of Astronomy

For April 2022, the first quarter moon is on April 8th. The Full Moon, the Paschal Moon, is on April 16th, and sets the next day as Easter Sunday. This is the first full moon after the Vernal Equinox. The Last Quarter Moon is on April 23rd. In the dawn sky, the waning crescent moon makes a triangle below Saturn (to right) and Mars (right) on April 25th, then lies just below brilliant Venus and slightly fainter Jupiter in the South East about 45 minutes before sunrise on April 27, the second, third, and fourth brightest objects in the sky in the same binocular field of view! What a photo op! The New Moon is on April 30th.

Mercury is visible just below the Pleiades cluster in the NW starting the third week of April, and remains visible after sunset for the rest of the month. Venus is in the dawn sky, and is overtaking fainter Jupiter this month, passing within a moon’s diameter (.5 degrees) on April 30th, a fine sight with naked eyes, binocs, and low power telescopes! Note the four moons of Jupiter and the gibbous phase of Venus now. Mars lies in Aquarius in the dawn, and Saturn lies about 14 degrees west of Mars. On April 25th, Mars lies exactly half way between Saturn to the right and brilliant Venus to the lower right. The planets will finally start coming back into the evening skies by July.

Yellow Capella, a giant star the same temperature and color as our much smaller Sun, dominates the northwestern sky. It is part of the pentagon on stars making up Auriga, the Charioteer (think Ben Hur). Several nice binocular Messier open clusters are found in the winter milky way here. East of Auriga, the twins, Castor and Pollux highlight the Gemini. South of Gemini, Orion is the most familiar winter constellation, dominating the southern sky at dusk.

The reddish supergiant Betelguese marks his eastern shoulder, while blue-white supergiant Rigel stands opposite on his west knee. Just south of the belt, hanging like a sword downward, is M-42, the Great Nebula of Orion, an outstanding binocular and telescopic stellar nursery. The bright diamond of four stars that light it up are the trapezium cluster, one of the finest sights in a telescope. In the east are the hunter’s two faithful companions, Canis major and minor. Procyon is the bright star in the little dog, and rises minutes before Sirius, the brightest star in the sky. At 8 light years distance, Sirius is the closest star we can easily see with the naked eye.

To the northeast, look for the Big Dipper rising, with the top two stars of the bowl, the pointers, giving you a line to find Polaris, the Pole Star. Look for Mizar-Alcor, a nice naked eye double star, in the bend of the big dipper’s handle. But our feature photo for April lies just SE of the bottom pointer. It’s the bluish circular Owl Nebula (M-97, note the two eyes!) and the spiral galaxy, M-108 (the Surfboard); both these are visible with a 4" telescope.

For the moment, consider the depth of field here. Visually, which seems the closest, and how do we know? Because they show larger shapes, I think most would consider the round Owl and oval Surfboard closer than the points of light. The fainter stars we assume are more distant, and the brighter the closer. Both of these blurs are Messier objects, originally mistaken for comets by Charles Messier, but when they failed to move in orbit of the Sun, he cataloged them as things comet hunters should skip (Messier built his home on proceeds of awards by the King of France for his 21 cometary discoveries).

The round shape of the Owl caused the discoverer of green ball Uranus, William Herschel, to call it and similar round balls of glowing gas "planetary nebulae". Again their failure to move like planets revealed they were far more distant, outside the solar system. We know in fact it is more distant than many of the stars here, about 2,000 light years distant, and about a light year across. Its central star is collapsing to a white dwarf, about 20X hotter than our Sun, and 100X brighter. Our own solar system will probably pass through this stage in another 6 billion years, not a bad tomb stone.

The oval blur at left is like our Milky Way, a barred spiral, seen almost edge on, and similar in size, mass, and luminosity to our own Galaxy. At 14 million light years distance, it is also a member of the Ursa major galaxy cluster, like M-81 and M-82 featured last month. Our own Galaxy is a member of a similar cluster, the Local Group, extending outward about three million light years, and including the famed Andromeda Galaxy, M-31, the Large and Small Magellanic Clouds of the southern sky, and about 100 other much smaller, fainter dwarf elliptical and irregular companions. More are to be found with better scopes.

Take the pointers at the front of the dipper’s bowl south instead to the head of Leo, looking much like the profile of the famed Sphinx. The bright star at the Lion’s heart is Regulus, the "regal star". Now take the curved handle of the Big Dipper, and follow the arc SE to bright orange Arcturus, the brightest star of the spring sky. Recent studies of its motion link it to the Sagittarius Dwarf Galaxy, a companion of our Milky Way being tidally disrupted and spilling its stars above and below the plane of the Milky Way, much like dust falling away from a decomposing comet nucleus. So this brightest star of Bootes the Bear Driver is apparently a refugee from another galaxy, but also a member of our Local Group of Galaxies above.

Out at the edge of our Galaxy are hundreds of globular star clusters, and one of the finest lies just east of Arcturus. It is the third entry in Messier’s listing of smudges in the sky that did not move and thus were not his beloved comets. M-3 is visible as a compact blur in binoculars, and resolves itself into thousands of stars at about 100X in scopes six inches or larger. Many more globulars will join it in the eastern sky in the next few hours, with over 100 in range of amateur scopes.

Now spike south to Spica, the blue-white gem in Virgo rising in the SE. Virgo is home to many galaxies, as we look away from the obscuring gas and dust in the plane of the Milky Way into deep space. To the southwest of Spica is the four sided Crow, Corvus. To the ancient Greeks, Spica was associated with Persephone, daughter of Ceres, goddess of the harvest. She was abducted by her suitor Pluto, carried down to Hades (going to Hell for a honeymoon!) and when Jupiter worked out a compromise between the newlyweds and the angry mother-in-law, the agreement dictated Persephone come back to the earth’s surface for six months of the year, and Mama Ceres was again placated, and the crops could grow again. As you see Spica rising in the SE, it is time to "plant your peas", and six months from now, when Spica again disappears in the sun’s glare in the SW, you need to "get your corn in the crib"….so was set our calendar of planting and harvesting in antiquity.

Read past issues of the Sky at Night