S Orionis
Encyclopedia
S Orionis is a red giant
star in the constellation
Orion
. It is a Mira variable
that pulsates with a 420–day cycle, and varies in radius from 1.9 to 2.3 astronomical unit
s.
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
star 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....
Orion
Orion (constellation)
Orion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...
. It is a Mira variable
Mira variable
Mira variables , named after the star Mira, are a class of pulsating variable stars characterized by very red colors, pulsation periods longer than 100 days, and light amplitudes greater than one magnitude in infrared and 2.5 magnitude in visual...
that pulsates with a 420–day cycle, and varies in radius from 1.9 to 2.3 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s.