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Discovery of the First T Tauri Star
John Russell Hind was an astronomer with Greenwich Observatory and, later, Bishop's Observatory. He discovered the body, which he called a "small, nebulous looking object" --- the object that was later named T Tauri --- on Oct. 11, 1852. Further study showed that the object was not a nebula, but was in fact a variable star. The star took its name from its relative position in the Taurus constellation and the initial T, which indicates it is the third variable star in Taurus.
T Tauri Classification
Stars designated as T Tauri stars are low in mass, weighing from .5 to 2.0 solar masses, or from one-half to two times the mass of Earth's sun. They are called variable stars because their brightness ebbs and flows. Sometimes the dust and gas form into an object known as an accretion disk, which may evolve into a planetary system. T Tauri stars are less than 10 million years old. The two subtypes of T Tauri stars are classical and weak T Tauri stars.
Classical T Tauri Stars
A classical T Tauri star may be distinguished by the presence of a thick disk of gas and dust. This disk, called a protoplanetary disk by some astronomers, may eventually form into planets that revolve around the star. Classical T Tauri stars are very young stars --- younger than 3 million years.
Weak T Tauri Stars
The weak T Tauri stars are the adolescents of the class, at around 10 million years old. This subtype of T Tauri stars is also distinguished by the lack of a protoplanetary disk. As of this writing, astronomers do not know where the disks belonging to weak T Tauri stars go or how they dissipate; they can only say for certain that at one time, all T Tauri stars have such disks.