Spring 1999 The Spring Sky |
| Fixed Stars
Two fainter clusters, both also in the spring sky, illustrate this. The Coma Cluster, located in an empty part of the sky very near the north galactic pole and about 5 degrees west of beta Com is a compact cluster whose core is dominated by elliptical galaxies (the brightest of which are magnitude 12, and thus hard to find). The Hercules Cluster, which is even more distant and fainter, is in the south-eastern sky in the evening, about 7 degrees south-west of Kornephoros (beta Her). It is much less compact and is composed almost entirely of spirals. These differences have led to much speculation in the past. They now seem to be giving us important information about the ways different types of galaxies evolve. Planets Mercury will not be observable by northern observers until June, when it will be favorably located in the north-western evening sky. It will reach maximum elongation at the end of the month.Venus will spend the spring quarter in the evening sky, where it will be particularly well located for northern observers. It will reach maximum elongation in the middle of June. The distance above the horizon is greatest before that time, but the disk will become larger and the crescent shape more pronounced as it approaches inferior conjunction later in the year. Mars reaches opposition on April 24. This is not a particularly favorable opposition, the planet being at more than its average distance from the earth. Mars then moves into the evening sky and ends its retrograde motion in the beginning of June. Jupiter is in conjunction with the sun on April 1 and remains unobservable from the northern hemisphere until the middle of May, when it will appear in the morning sky. Saturn reaches conjunction with the sun on April 27, and is thus visible only with difficulty in the evening twilight at the beginning of the month and in the morning sky after the middle of June. Those who still like to think of Pluto as a planet [see the Winter 1998 Newsletter, p. 7 –Ed.] will want to note that it is in opposition on May 31. Meteor ShowersNo meteor showers of note are expected during the spring. The Lyrids will be visible for a few days around April 22 and the eta-Aquarids for about 2 weeks around May 5. The latter will be visible only in the morning and will be competing with a bright moon, nearing last quarter. EclipsesThere will be no eclipses during the spring quarter, but we hope that as many readers as possible have made plans to see the total solar eclipse on August 11, which will pass over the Black Sea and Turkey. In fact, MIRA will be sending a benefit tour to Turkey to see this eclipse. |
With the Milky Way largely below the horizon during the spring, it is time
once again to get out our largest telescopes and look at the galaxies. The most prominent
concentration is the Virgo Cluster, to be found somewhat south of the zenith in the
evening sky. It is about halfway between Arcturus and Regulus and about 10
degrees east of Denebola. There are 15 Messier galaxies in or close to the Virgo
Cluster, but none is visually spectacular. The brightest is the outlying elliptical galaxy
M49, but almost as bright and much more interesting is the central giant elliptical M87.
As is the case with many clusters, the core of the Virgo Cluster is dominated by a single
giant elliptical, which is also an active galaxy. Indeed, M87 is one of the strongest
radio sources in the sky (Virgo A) and shows a jet in both optical and radio
radiation, indicating ejection of matter at a high velocity. This could be due to the
capture of surrounding galaxies, mostly small spirals, whose gas is fed into the center
where it is captured by a massive black hole, causing the observed activity. This would
explain the absence of spiral galaxies from the centers of compact clusters. 