ESO Astronomical Glossary - L
Large Magellanic Cloud
The Large Magellanic Cloud (LMC) is a dwarf galaxy, spiral in shape, that orbits the Milky Way galaxy at a distance of around 160,000 light years. The LMC and its twin, the Small Magellanic Cloud, are two of our most prominent galactic neighbours.
La Silla is the site of ESO's first observatory in Chile, inaugurated in 1969. It is located 160 km North of the town of La Serena at an altitude of 2,400 m. Today six telescopes are in operation at the observatory, including the New Technology Telescope (NTT), in which the technique of active optics was first pioneered, and the 3.6 m Telescope operating the ultra-precise planet-finding instrument HARPS.
A light year, often abbreviated 'ly', is a unit to measure distance and corresponds to the distance light travels in a vacuum in one year, equivalent to approximately 9.46053 x 1012 kilometers (9.5 thousand billion km).
The Local Group is the small cluster of galaxies that our Milky Way galaxy belongs to. Measuring about 10 million light years across, it is dominated by the Milky Way and Andromeda galaxies. It also contains more than 30 dwarf galaxies.
Luminosity is the total brightness of a star or other astronomical object. It is expressed in Watts (symbol 'W') and represents the total amount of energy that the object radiates each second over all wavelength regions of the electromagnetic spectrum. Luminosity is a physical property of the object and does not depend on the distance it is being observed from.