Ursa Major
Overview
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
visible throughout the year in most of the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
. It can best be seen in April. It is dominated by the widely recognized asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
known as the Big Dipper
Big Dipper
The Plough, also known as the Big Dipper or the Saptarishi , is an asterism of seven stars that has been recognized as a distinct grouping in many cultures from time immemorial...
or Plough, which is a useful pointer toward north
North
North is a noun, adjective, or adverb indicating direction or geography.North is one of the four cardinal directions or compass points. It is the opposite of south and is perpendicular to east and west.By convention, the top side of a map is north....
, and which has mythological significance in numerous world cultures.
The seven brightest star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s of Ursa Major form the asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
known as the Big Dipper
Big Dipper
The Plough, also known as the Big Dipper or the Saptarishi , is an asterism of seven stars that has been recognized as a distinct grouping in many cultures from time immemorial...
in the United States and Canada, or the Plough in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
.
Another asterism is recognized in Arab culture, a series of three pairs of stars:
- νNu Ursae MajorisNu Ursae Majoris is a binary star in the constellation Ursa Major. It is approximately 400 light years from the Earth.The primary component, Nu Ursae Majoris A, is an orange K-type giant with an apparent magnitude of 3.5m...
and ξXi Ursae MajorisXi Ursae Majoris is a star system in the constellation Ursa Major. On May 2, 1780, Sir William Herschel discovered that this was a binary star system, making it the first such system ever discovered...
Ursae Majoris, Alula Borealis and Australis, the "first leap"; - λLambda Ursae MajorisLambda Ursae Majoris is a star in the constellation Ursa Major. It also has the proper names Tania Borealis meaning "the Northern of Tania." The word Tania comes from the Arabic phrase al-Thāniyah meaning "the Second " , and Alkafzah...
and μMu Ursae MajorisMu Ursae Majoris is a star in the constellation Ursa Major. It also has the proper names Tania Australis meaning "the Southern of Tania." The word Tania comes from the Arabic phrase al-Thāniyah meaning "the Second " , Alkafzah...
Ursae Majoris, Tania Borealis and Australis, the "second leap"; - ιIota Ursae MajorisIota Ursae Majoris is a star system in the constellation Ursa Major. It is approximately 47.7 light years from Earth. It has the traditional names Talitha, Talitha Borealis and Alphikra Borealis, and was also named Dnoces after Edward H. White II, an Apollo 1 astronaut...
and κKappa Ursae MajorisKappa Ursae Majoris is a binary star in the constellation Ursa Major. It is approximately 423 light years from Earth and has the traditional names Talitha Australis, Al Kaprah, and Alphikra Australis....
Ursae Majoris, Talitha Borealis and Australis, the "third leap".
These stars are found along the southwest border of the constellation.
Except for Dubhe and Alkaid, the stars of the Big Dipper all have proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
s heading towards a common point in Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
.
Unanswered Questions