was delineated by Johannes Hevelius to represent Asterion and Chara, the two dogs of Boötes as he hunted the northern skies for the bears, Ursa Major and Ursa Minor. You can find these hounds by looking to the right of Boötes and south of the tail of the Great Bear. But you will have to look closely, for the brightest star of the 23 that Hevelius described is but magnitude 2.9. This is Cor Carolia fine double star. If, on a mid-May evening at about 9:30 or ten o'clock, you were to drop a plumb bob from Cor Caroli, it would come to Earth somewhere in the vicinity of Sonoma or Napa, in Northern California. It was Edmond Halley who named Cor Caroli in honor of King Charles II of England.
There are only two other stars bright enough to merit names of their own. Chara is Beta-Canum Venaticorum; and there is a star of magnitude 5.5 that has been called La Superba, a peculiar type of star with superbly flashing brilliancy of its prismatic rays. It is a brilliant red star whose light varies over a period of half a year between magnitude 5.2 and 6.6.
But what the Hunting Dogs lack in bright stars, they make up for with a wealth of galaxies. Five Messier objects are among the hundred deep-sky objects that may be found with even a small telescope. M51 is the Whirlpool Galaxy (NGC 5194), one of two connected galaxiesa pretty face-on spiral galaxy joined at the end of one of its spiral arms to the irregular galaxy NGC 5195. A 10- or 12-inch telescope and a dark sky are needed to discern the spiral arms, while smaller telescopes or large binoculars should reveal two fuzzy dots.
The Hubble Space Telescope has snapped a view of several star generations in the central region of the Whirlpool Galaxy (M51), a spiral region 23 million light-years from Earth in the constellation Canes Venatici. The galaxys massive center, the bright ball of light in the center of the photograph, is about 80 light-years across and has a brightness of about 100 million Suns. Astronomers estimate that it is about 400 million years old and has a mass 40 million times that of our Sun. The concentration of stars is about 5,000 times higher than in our solar neighborhood, the Milky Way. The dark Y across the center is a sign of dust absorption. The bright dot in the middle of the Y has a brightness of about one million suns, but a size of less than five light-years. Its power and its tiny size suggest that we have located the elusive central black hole that produces powerful radio jets. Surrounding the center is a much older stellar population that covers a region of about 1,500 light-years in diameter and is at least 8 billion years old, possibly as old as the Universe itself, about 13 billion years. Further away, there is a necklace of very young star-forming regions, clusters of infant stars, younger than 10 million years, which are about 700 light-years away from the center. Normally, young stars are found thousands of light-years away. Astronomers believe that stars in the central region were formed when a dwarf companion galaxywhich is not in the photographpassed close to it, about 400 million years ago, stirring up dust and material for new star birth.
The spiral nature of this
galaxy was the first such to be discovered. In 1845, Lord William
Parsons, the Irish Earl of Rosse, made the observation with his
reflecting telescope that had a mirror diameter of six feet. As
was William Herschel, Lord Rosse was a British amateur astronomer;
but unlike Herschel, he was a wealthy landowner with the means
to devote his time and money to his interests. The instruments
that Lord Rosse designed and built were enormous machines supported
by derricks and chains.
The large globular cluster, M3 (NGC 5272), shows as a pretty ball of sparkling points in this CCD photo by Conrad Jung, taken with his 6-inch Maksutov.
M63, M94 and M106 are also
spiral galaxies; and M3 is a bright globular cluster of stars
200 light years across and 35,000 light years distant. It is located
almost on a straight line and a little over half way between Cor
Caroli and Arcturus.