Andromeda I
Encyclopedia
Andromeda I is a dwarf spheroidal galaxy
(dSph) about 2.40 million light-year
s away in the constellation
Andromeda
. Andromeda I is part of the Local group of galaxies and a satellite galaxy
of the Andromeda Galaxy
(M31). It is roughly 3.5 degrees south and slightly east of M31. As of 2005, it is the closest known dSph companion to M31 at an estimated projected distance of ~40 kpc.
Andromeda I was discovered by Sidney van den Bergh
in 1970 with the Mount Palomar Observatory 48-inch telescope
. Further study of Andromeda I was done by the WFPC2 camera
of the Hubble Space Telescope
. This found that the horizontal branch
stars, like other dwarf spheroidal galaxies were predominantly red. From this, and the abundance of blue horizontal branch
stars, along with 99 RR Lyrae
stars detected in 2005, lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr
. The Hubble telescope also found a globular cluster
in Andromeda I, being the least luminous galaxy where such a cluster was found.
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
(dSph) about 2.40 million light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away 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....
Andromeda
Andromeda (constellation)
Andromeda is a constellation in the northern sky. It is named after Andromeda, the princess in the Greek legend of Perseus who was chained to a rock to be eaten by the sea monster Cetus...
. Andromeda I is part of the Local group of galaxies and a satellite galaxy
Satellite galaxy
A satellite galaxy orbits a larger galaxy due to gravitational attraction. Although a galaxy is made of a large number of objects which are not connected to each other, it has a center of mass, which represents a weighted average of the positions of each component object...
of the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
(M31). It is roughly 3.5 degrees south and slightly east of M31. As of 2005, it is the closest known dSph companion to M31 at an estimated projected distance of ~40 kpc.
Andromeda I was discovered by Sidney van den Bergh
Sidney van den Bergh
Sidney Van den Bergh, OC, FRS is a retired Canadian astronomer.Born in the Netherlands, son of businessman and politician Sidney James van den Bergh and grandson of Unilever co-founder Samuel van den Bergh, he showed an interest in science from an early age, learning to read with books on astronomy...
in 1970 with the Mount Palomar Observatory 48-inch telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
. Further study of Andromeda I was done by the WFPC2 camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
of the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
. This found that the horizontal branch
Horizontal branch
The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
stars, like other dwarf spheroidal galaxies were predominantly red. From this, and the abundance of blue horizontal branch
Horizontal branch
The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
stars, along with 99 RR Lyrae
RR Lyrae
RR Lyrae is a variable star in the Lyra constellation. It is the prototype of the RR Lyrae variable class of stars. It has a period of about 13 hours, and oscillates between apparent magnitudes 7 and 8. Its variable nature was discovered by the Scottish astronomer Williamina Fleming at Harvard...
stars detected in 2005, lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr
Byr
Byr was formerly used in English-language geology and astronomy as a unit of one billion years. The "B" is an abbreviation for "billion" , with "yr" simply an abbreviation for "year". Today, the term gigaannum is also used, but Gy or Gyr are still sometimes used in English-language works...
. The Hubble telescope also found a globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
in Andromeda I, being the least luminous galaxy where such a cluster was found.