Close-up on CED 173, the Tulip Nebula

The Tulip Nebula (also known as Sh2-101) is a visible emission nebula in the constellation Cygnus.

It is located in the central-southern part of the constellation, at the center of a very bright stretch of the Milky Way rich in star fields; It is located about 45' northeast of the star η Cygni and extends about twenty primes in a NE-SW direction. It has an elongated and irregular shape; The best time to observe it in the evening sky is between the months of June and November.

It is a large H II region located on the initial stretch of the Orion Arm about 2700 parsecs (8750 light-years) away from the solar system, beyond the large Cygnus X nebula complex, from which it would be no more than 500 parsecs. This distance coincides with that estimated for the OB Cygnus OB3 association, which contains about thirty massive stars of the first spectral classes with an age of about 8.3 million years. The source of ionizing radiation in the nebula's gases is believed to be the star HD 227018, a blue giant of class O6.5III with an apparent magnitude of 9.01. According to the Avedisova catalogue, the nebula hosts some active star formation phenomena, as evidenced by the presence of four sources of infrared radiation reported in the IRAS catalogue: IRAS 19581+3504, IRAS 19579+3509, IRAS 19584+3506 and IRAS 19584+3515, as well as some radio wave sources.