09 April 2004

Eye on the Sky

Paul Curtin

A Reminder: If you are interested in observing the transit of Venus this June, you should start a regular observing plan now in order to avoid technical surprises on the big day. Also remember to check local times for this event, as much of North America will have a tiny window at sunrise. Choose your observing site carefully!

The April Sky: Realm of galaxies

Having examined the open clusters of Canis Major, Gemini and Cancer, we now turn our gaze far beyond the Milky Way to the galaxies and systems of galaxies of the spring sky. Leo is composed of a sickle facing westward followed by a right triangle. East of this is Coma Berenices, an open cluster so near to us that it appears as a small constellation. Follow the handle of the Big Dipper through dazzling Arcturus in Bootes and further to Spica in Virgo. North and west of Spica one observes a faint but distinct string of stars forming a large Y shaped asterism. Within the arms of the Y lies the heart of the Virgo cluster. A very clear, dark night and the largest telescope available are needed to fully appreciate this region of the sky.

The Virgo cluster of galaxies stretches across a large area in Leo, Virgo and Coma Berenices. This large system includes our own Local Group. Begin by sweeping slowly in the area just east of Regulus, then continue on to the regions west and northwest of Spica. Finally, sweep Coma first with binoculars and then with the telescope. Bear in mind that some of the galaxies visible belong to the Virgo group while others make up the Coma Berenices group.

A survey of Ursa Major likewise reveals galaxies in the Virgo group and others, especially near the bowl of the Big Dipper, associated with the Ursa Major group. Start with a wide view and check for fuzzy patches. When you locate a candidate, try a higher power to see if any structural characteristics can be distinguished. Keep track of the sky conditions, magnification and equipment details, and try your hand at drawing groups and individual galaxies. Those wishing to pursue this line of observation should refer to Kepple for detailed charts and Jones, volumes 4 and 5, for techniques and long term observing programs.

Southern observers have a great month for observing dark lanes within the very bright section of the Milky Way passing through Carina, Vela and Centaurus. Whereas northern observers have the monopoly on galaxies this month, the southern sky abounds in open and globular clusters.

Observers from Southern Africa to Antarctica will get to observe a partial solar eclipse on April 19. See Gupta for times and other details.

The planets this month

Mercury is lost in the Solar glare for most of April. Venus is the extremely bright object in the West after sunset. Look for it just South of the Pleiades early in the month. It displays more of a crescent as the month progresses, reaching maximum in May.

Mars, now but a ruddy shadow of its former glory, is in Taurus and sets before midnight. On April 7th it comes close to Aldeberan, the brightest star in Taurus. This will be a great opportunity to compare the red hues of these objects.

Jupiter is in Leo and continues to be well placed for telescopic observation. It will remain very bright throughout the Spring.

Saturn is in Gemini, and is also very well placed for observation.

Bibliography

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

Gupta, R. (ed.) Observers Handbook 2004. Toronto: University of Toronto Press, 2003.

Jones, K. G. (ed.) Webb Society Deep-Sky Observers Handbook. Enslow Publishers, 1982.

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

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