Hydra is the longest and largest constellation at 1303 square degrees. It spans over 6 hours of right ascension or approximately 1/4 the circumference of the sky and is visible in the winter and spring in the northern hemisphere.
The widely scattered stars of Collinder 285 (the Ursa Major Moving Cluster) cover a considerable portion of the heavens but I have never seen its component stars, which are found in constellations such as Ursa Major, Draco, Corona Borealis, Leo Minor, and Canis Major, listed on any star chart as an aggregate. An even larger object is Gould's Belt, a ring of very luminous B-type stars inclined by about 20 degrees in relation to the galactic plane at the Sun's location and centered roughly on its position in the galaxy. Again something that I have never seen charted in a star atlas as a single entity.
The only non-Milky Way grouping that I know of that encompasses the entire sky is the zodiac, the band of the 12 traditonal constellations that astrologers use as "signs" to spin their fantasies. The ecliptic, the apparent path of the Sun and the planets through the celestial sphere, runs through the zodiacal constellations. BTW, there are actually as many as 20 constellations, using the astronomical definition, involved in the zodiac if the 3 outer gas giants unknown to ancient astrologers are included. The celestial equator and the colures also encompass the entire sky but these are intellectual constructs too.
The extremely faint ring of interplanetary dust known as the zodiacal band, which includes the relatively easy to see zodiacal light and the far more difficult gegenschein or counterglow, is visible only at the world's best dark sky sites.
Dave Mitsky
__________________
Chance favors the prepared mind.
De gustibus non est disputandum.
Never attribute to malice that which can be adequately explained by stupidity.
|