The April Sky

Paul Curtin

Special Alert

The asteroid 2006 VV2 comes closer to earth than any other known asteroid until May 2036. 2006 VV2 will pass east of the galaxies M82, then M81 on 29 March, then 15 degrees east of beta Leo Minoris on 30 March. The asteroid, at 10th magnitude, will be visible in mid-sized telescopes.


Noteworthy Events this Month

For observers in the far north, Saturn will be occulted on 25 April.

Northwest North America will have the opportunity to watch the Moon occult Regulus on 26 April.

The April Sky

Spring in the Northern Hemisphere finds our gaze fixed far from the arms of our galaxy. This means that, apart from some errant globular clusters and planetary nebulae, we are presented with a staggering number of galaxies, some bright, most very faint, all worth seeking if only to test your technique and your local sky conditions.

Start with the unmistakable “Big Dipper.” The five interior stars are members of the Ursa Major Moving Group (which also includes Sirius, beta Eridani, and delta Aquarii). Zeta and xi are double stars. Ursa Major contains a huge number of galaxies, some rather difficult to locate. The brighter include M81, M82, M108, M109, and M101 (the Pinwheel Galaxy). Noteworthy also is the planetary M97, the Owl Nebula.

South of the dipper’s handle is Canes Venatici. Alpha, “Cor Caroli”, is double. Look for the galaxies M51 (“Whirlpool”), M63 (“Sunflower”), M106, M94, and NGC 4490 (“Cocoon”). Closer to home is M3, a fine globular cluster.

In dark skies the region west of Arcturus, east Leo’s triangle, shimmers with the faint but extended open cluster Melotte 111. This cluster makes up the main part of Coma Berenices. After viewing this nice binocular object, look for the galaxies M98, M99, M100, M85, M88, M91, M64 (“Black-Eye”), and M53.

The western section of Virgo is a large Y-shaped form with bright Spica (alpha Virginis) at its base. One would need to consult a special chart of the Virgo Cluster of Galaxies to truly appreciate the immensity of this celestial object. See Jones or Kepple and Sanner for finder charts. Among a host of galaxies, M104 (“Sombrero”), M90 and M89 stand out.

Corvus and Crater hover north of Hydra. Corvus is a small box-shaped constellation. It contains some double stars and a small number of galaxies. Crater, a celestial goblet, has few deep-sky objects of note. Gamma is a fine double. We met Hydra last month, the central section contains some multiple stars and faint galaxies. With binoculars, sweep west to east and follow some of the attractive star strings that seem like tiny sprites in the wake of the water snake.

Unlike the dark but galaxy rich skies in the north, the southern sky is dominated by our own Milky Way. Crux is a show piece item. Amidst the open clusters, notably the “Jewel Box” NGC 4755, is the dark nebula known as the “Coalsack.” South of Crux is Musca, rich in a dazzling array of Milky Way objects, its southern edge blends in with the dark, star-poor regions of Chameleon.

The Planets in April

Mercury can best be viewed by southern observers in the morning sky.

Venus is an impressive evening object. Look for it near the crescent Moon on 19 April.

Mars is in the morning sky.

Jupiter rises late in the evening and can be viewed best in the morning sky.

Saturn is the highlight of the evening sky. Consult Kelly for satellite positions.

Bibliography

Burnham, Robert Jr., Burnham's Celestial Handbook, New York: Dover, 1978.

Kelly, P. (ed.), Observers Handbook 2007, Toronto: University of Toronto Press, 2006.

Kepple, G. R., Sanner, G. W., The Night Sky Observers Guide, Richmond, Virginia: Willman-Bell, 1999.

Tirion, W., Rappaport, B., Remaklus, W., Uranometria Deep Sky Atlas, Richmond, Virginia: Willman-Bell, 2000.

Webb, T. W., Celestial Objects for Common Telescopes, New York: Dover, 1962