NGC 6791
Encyclopedia
NGC 6791 is an open star cluster
in the Lyra constellation. It was discovered by Friedrich August Theodor Winnecke
in 1853. At roughly 8 billion years old, and with an Iron
to Hydrogen
abundance
ratio that is more than twice that of the Sun
, it is one of the oldest and most metal-rich
clusters in the Milky Way
. This is contrary to the typical rule-of-thumb where older means more metal-poor. Compounded with the fact that it has an unusually high population of stars, NGC 6791 is among the most studied clusters in the sky.
In March 2009 NASA launched the Kepler Mission spacecraft. This spacecraft is a dedicated mission to discover extrasolar planets by the transit method from solar orbit. In April 2009 the project released the first light images from the spacecraft and NGC 6791 was one of two objects highlighted.
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
in the Lyra constellation. It was discovered by Friedrich August Theodor Winnecke
Friedrich August Theodor Winnecke
Friedrich August Theodor Winnecke was a German astronomer.He worked at Pulkovo Observatory from 1858 to 1865, but returned to Germany and served as professor of astronomy at Strasbourg from 1872 to 1881.He discovered or co-discovered a large number of comets, including the periodic comet...
in 1853. At roughly 8 billion years old, and with an Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
to Hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
abundance
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...
ratio that is more than twice that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, it is one of the oldest and most metal-rich
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
clusters in the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. This is contrary to the typical rule-of-thumb where older means more metal-poor. Compounded with the fact that it has an unusually high population of stars, NGC 6791 is among the most studied clusters in the sky.
Age studies
Among the dimmest stars in the cluster are groups of white dwarfs that are 6 billion years old and another group that appear to be 4 billion years old. The ages are out of sync with those of the cluster's normal stars, which are 8 billion years old. This seeming contradiction in age for this cluster has been studied and a solution proposed with age of about 8 billion years.The Kepler Mission