Leo I is a dwarf spheroidal galaxy in the constellation Leo. At about 800,000 light years distant, it is a member of the Local Group of galaxies and is thought to be one of the most distant satellites of the Milky Way galaxy. It was discovered in 1950 by Wilson on photographic plates of the National Geographic Society - Palomar Observatory Sky Survey, which were taken with the 48-inch Schmidt camera at Palomar Observatory. ^{[1] [2]} In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... Right ascension (RA; symbol α: Greek letter alpha) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. ... In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. ... To help compare different orders of magnitude, this page lists distances starting at 1021 m (1 Zm or 110,000 light years). ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to that of the Sun (left). ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... It has been suggested that milliarcsecond be merged into this article or section. ... Orion is a remarkable constellation, visible from most places on the globe at one time or another during the year. ... Leo (Latin for lion, symbol , Unicode ♌) is a constellation of the zodiac. ... RADIUS (Remote Authentication Dial In User Service) is an AAA (authentication, authorization and accounting) protocol for applications such as network access or IP mobility. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us. ... Dwarf spheroidal galaxy (dSph) is a term in astronomy applied to the nine low luminosity dwarf elliptical galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31. ... Orion is a remarkable constellation, visible from most places on the globe at one time or another during the year. ... Leo (Latin for lion, symbol , Unicode ♌) is a constellation of the zodiac. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... Map of the local group The Local Group is the group of galaxies that includes our galaxy, the Milky Way. ... Note: This article contains special characters. ... Albert George Wilson (July 28, 1918 – ?) was an American astronomer. ... Photographic plates were one of the earliest forms of photographic film, in which a light-sensitive emulsion of silver salts was applied to a glass plate. ... The National Geographic Society - Palomar Observatory Sky Survey (NGS-POSS) is a major photographic survey of the night sky completed at Palomar Observatory in 1958. ... 2m Schmidt Camera (Alfred-Jensch-Telescope Tautenburg, Thuringia, Germany A Schmidt camera is an astronomical camera designed to provide wide fields of view with limited aberrations. ... Palomar Observatory is a privately-owned observatory located in San Diego County, California, 90 miles (145 km) southeast of Mount Wilson Observatory, on Palomar Mountain. ...

The measurement of radial velocities of some bright red giants in Leo I have made possible to measure its mass. It was found to be at least (2.0 ± 1.0) × 10⁷ M_Sun. The results are not conclusive, and do not deny or confirm the existence of a large dark matter halo around the galaxy. However, it seems to be certain that the galaxy does not rotate. ^[2] Radial velocity is the velocity of an object in the direction of the line of sight. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... The Sun is the star at the center of Earths solar system. ... In cosmology, dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. ...

It has been suggested that Leo I is a tidal debris stream in the outer halo of the Milky Way. This hypothesis has not been confirmed, however. ^[2] The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ...

Typical to a dwarf galaxy, the metallicity of Leo I is very low, only one percent that of the Sun. It seems that the galaxy experienced a major increase in its star formation rate between 6 Ga and 2 Ga (billion years ago). Some low-level activity may have continued until 200-500 Ma. Therefore it may be the youngest dwarf spheroidal satellite galaxy of the Milky Way. In addition, the galaxy may be embedded in a cloud of ionized gas with a mass similar to that of the whole galaxy. ^[2] In astronomy, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. ... The Sun is the star at the center of Earths solar system. ... Annum is a Latin noun meaning year. ...

No globular clusters have been found in the galaxy. ^[2] A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ...

Leo I is located only 12 arc minutes from Regulus, the brightest star in the constellation. For that reason, the galaxy is sometimes called the Regulus Dwarf. Scattered light from the star makes studying the galaxy more difficult, and it was not unti the 1990s that it was detected visually. ^{[1] [2]} It has been suggested that milliarcsecond be merged into this article or section. ... Regulus (α Leo / α Leonis / Alpha Leonis) is the brightest star in the constellation Leo and one of the brightest stars in the nighttime sky. ...

References

1. ^ ^a b "Leo I." SEDS Messier Database. URL accessed on 2006-05-15.
2. ^ ^{a b c d e f} Van den Bergh, Sidney (2000). Galaxies of the Local Group, 1st edition, 243 – 245, Cambridge University Press. ISBN 0521651816.

2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... May 15 is the 135th day of the year in the Gregorian Calendar (136th in leap years). ...

External links

• Astronomy Picture of the Day - Leo I
• SEDS page on Leo I