A cometary globule is a reflection nebula with a dusty head and a fan-shaped tail that bears a superficial resemblance to a comet. Cometary globules are often the birthplaces of stars, and many show very young stars in their heads. Classical examples of the heads of cometary nebulae are R Monocerotis in Hubble's Variable Nebula, R Coronae Australis, and RY Tauri. All have A0 to G0 type spectra that resemble the spectrum of a T Tauri star, and show brightness variations from year to year.