Post by glactus on Feb 17, 2008 5:06:25 GMT
Ursa Major is a constellation visible throughout the year in most of the northern hemisphere. Its name means Great Bear in Latin, and is associated with the legends of Callisto and Cynosura. This stunnimg constellation boasts at least 50 galaxies to view for the amateur astronomer including 7 Messier objects.
The seven brightest stars, located in the Bear's hindquarters and tail, form the well-known Big Dipper asterism. In Britain, this asterism is known as the Plough.
Notable stars:
47 Ursae Majoris
47 Ursae Majoris is a yellow dwarf star similar to our Sun and located at a distance of approximately 46 light-years. This star is known to have two extrasolar planets orbiting it and is ranked 72nd in the list of top 100 target stars for the NASA Terrestrial Planet Finder mission. Absolute magnitude is 4.25.
W Ursae Majoris
W Ursae Majoris, a variable star, is an eclipsing contact binary whose two component stars share a common outer layer, and is the prototype of a class of contact binary variables known as W Ursae Majoris variables. The contact nature makes it impossible to tell when an eclipse of one component by the other starts or ends precisely. During an eclipse its apparent magnitude ranges between 7.75 and 8.48 over a period of 8 hours. Distance from Earth is 162 light years.
Mizar
Mizar is the star that is the second star from the end of the Big Dipper's handle. The name comes from the Arabic meaning a waistband or girdle. Mizar has apparent magnitude 2.27 and is of spectral class A1 V. Distance from Earth is 78 light years.
Alcor
With good eyesight one can make out a faint companion just to the east of Mizar called Alcor or 80 Ursae Majoris. Alcor has magnitude 3.99 and spectral class A5 V. The two are often called the horse and rider and lie more than a quarter of a light year apart. Although proper motions show they move together, it is still not known whether they form a true binary star system.
Notable objects:
Messier M 81
Messier M81, also known as NGC 3031 or Bode's Galaxy, is a spiral structure about 12 million light-years away from Earth. M81 is one of the most striking examples of a grand design spiral galaxy, with near perfect arms spiraling into the very center. Because of its close proximity to Earth, its large size, and its active galactic nucleus which may harbor a supermassive black hole, Messier 81 is a popular galaxy to study in professional astronomy research. The galaxy's large size and relatively high apparent magnitude also make it a popular target for amateur astronomy observations. Magnitude is 6.9.
Messier M 82
Messier 82, also known as NGC 3034 or the Cigar Galaxy, is a starburst galaxy laying at a distance of about 12 million light-years. Forming a striking pair in small telescopes with nearby M81, M82 is being physically affected by its bigger neighbor. Tidal forces caused by gravity have deformed this galaxy, a process that started about 100 million years ago. This interaction has caused star formation to increase 10 fold compared to "normal" galaxies. Astronomers have postulated that the fluctuating emission which comes from the core of M 82 is the first known intermediate-mass black hole, of roughly 200 to 5000 solar masses. Magnitude is 9.3.
Messier M 101 - The Pinwheel Galaxy
The Pinwheel Galaxy, also known as Messier 101 or NGC 5457, is a face-on spiral galaxy which lies at a distance of about 27 million light-years. It was discovered by Pierre Mechain on March 27, 1781, and Charles Messier verified its position and added it to the Messier Catalogue as one of the final entries. On February 28, 2006, NASA and the ESA released this very detailed image of the Pinwheel Galaxy from 51 individual exposures, plus some extra ground-based photos. Apparent magnitude is 8.3.
Messier M 97 - The Owl Nebula
The Owl Nebula, also known as Messier Object 97 or NGC 3587, is a planetary nebula discovered by Pierre Mechain in 1781. M97 is regarded as one of the more complex of the planetaries and formed roughly 6,000 years ago. The nebula gets it name due to the appearance of owl-like "eyes" when viewed through a 200 mm (8 inch) telescope under dark sky conditions with the aid of a so-called "nebula filter." The "eyes" are also easily visible through photographs taken of the nebula. Distance from Earth is 2,600 light years, and magnitude 9.9.
M 82
credits:
Ursa Major map: Wikipedia
en.wikipedia.org/wiki/Ursa_Major
image: Messier M81:wikipwedia: HST/NASA/ESA.
en.wikipedia.org/wiki/Image:M81hub.jpg
image: Messier M 82:A combined Hubble/Spitzer/Chandra image: NASA/JPL-Caltech/STScI/CXC/UofA/ESA/AURA/JHU. Wikipedia en.wikipedia.org/wiki/Messier_82
image: Messier M101: The Pinwheel Galaxy:
NASA/ESA.wikipedia
en.wikipedia.org/wiki/Pinwheel_Galaxy
image: Messier M 97 - The Owl Nebula:
cseligman: AURA, NSF, NOAO
cseligman.com/text/stars/messiernebulae.htm