Leo I is a dwarf spheroidal galaxy discovered in 1950 by Albert George Wilson on photographic plates of the National Geographic Society – Palomar Observatory Sky Survey. 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. The galaxy is located only 12 arc minutes from Regulus, the brightest star in the constellation Leo, which makes it challenging to observe due to scattered light. Despite its small size, Leo I has been the subject of extensive research, providing valuable insights into galaxy formation and evolution.
Names and Catalog numbers
- Regulus Dwarf
- UGC 5470
- PGC 29488
Position and the cosmic neighborhood
Leo I is situated in the constellation Leo, positioned just 12 arc minutes north of the bright star Regulus (α Leonis). This proximity to Regulus makes Leo I an excellent test object for sky transparency and telescope contrast performance. The galaxy is part of the Local Group and is considered a distant companion of our Milky Way. Its location in the spring sky makes it a popular target for galaxy observers during the “galaxy season.”
Nice to Know
- Leo I experienced a major increase in its star formation rate between 6 billion and 2 billion years ago, accounting for 70% to 80% of its stellar population.
- The galaxy has an unusually low metallicity, only about 1% that of the Sun, indicating its stars are very old.
- Leo I may be embedded in a cloud of ionized gas with a mass similar to that of the whole galaxy.
- Some studies suggest the presence of a black hole of three million solar masses in the center of Leo I, which would be significant as it would be the first time this has been observed in a dwarf spheroidal galaxy.
Brightness, distance and size
Leo I has a visual magnitude of 11.1, making it a challenging but achievable target for amateur astronomers with medium-sized telescopes. Located approximately 820,000 light-years from Earth, it is one of the most distant satellite galaxies of the Milky Way. The galaxy spans about 9.9 by 7.5 arcminutes in the night sky, which translates to a physical size of roughly 2,000 light-years across. Despite its relatively small size compared to larger galaxies, Leo I’s apparent size in the sky makes it an interesting target for astrophotography, especially when capturing its context within the Leo constellation.
