W Ursae Majoris
Encyclopedia
W Ursae Majoris (W UMa) is a variable star
in the constellation
Ursa Major
. It 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 variable
s. Unlike with normal eclipsing binaries, 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. Because the two components share their outer layers, they have the same stellar classification
, and are classified as yellow F-type main sequence dwarfs
.
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
in the constellation
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....
Ursa Major
Ursa Major
Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
. It is an eclipsing contact binary
Contact binary
In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontact binary...
whose two component stars share a common outer layer, and is the prototype of a class of contact binary
Contact binary
In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontact binary...
variables known as W Ursae Majoris variable
W Ursae Majoris variable
A W Ursae Majoris variable is a type of eclipsing binary variable star. These stars are close binaries, whose surfaces are in contact with one another. They are termed contact binaries because the two stars touch and they essentially share material in their outer layers. Through the neck between...
s. Unlike with normal eclipsing binaries, 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
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
ranges between 7.75 and 8.48 over a period of 8 hours. Because the two components share their outer layers, they have the same stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
, and are classified as yellow F-type main sequence dwarfs
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
.