In October 1852, J. R. Hind `noticed a very small nebulous looking
object' roughly 18 arcsec west of a tenth magnitude star in Taurus.
Over the next 15 years, the nebula slowly faded in brightness and
in 1868 vanished completely from the view of the largest telescopes.
O. Struve then found a new, smaller and fainter, nebulosity roughly
4 arcmin west of Hind's nebula. While trying to recover these nebulae,
S. Burnham discovered a small elliptical nebula surrounding T Tau.
Spectra of Hind's nebula revealed a single emission line from either
Hydrogen or Oxygen, demonstrating that the nebula was gaseous as in
novae and planetary nebulae. At about the same time, G. Knott reported
factor of 40 variations in the brightness of the `ruddy' star associated
with these nebulae, T Tauri.
In the 1940's, A. Joy compiled the first lists of `T Tauri stars,'
irregular variable stars associated with dark or bright nebulosity, with
F5-G5 spectral types and low luminosity .
Intense searches for other T Tauri stars revealed many stars
associated with dark clouds and bright nebulae, including a class
with A-type spectra. Most of these stars were in loose groups, the
T associations, or in dense clusters, the O associations. All O stars
have short lifetimes. Thus, both types of associations must be
composed of young stars, with ages of 10 Myr or less. This realization
-- now 50 years old -- initiated the study of star formation in dark clouds.
Next: structure of the Taurus-Auriga dark clouds