Messier 21 - Open Cluster in Sagittarius
Messier 21 is a Open Cluster in the Sagittarius constellation. Messier 21 is situated close to the celestial equator and, as such, it is at least partly visible from both hemispheres in certain times of the year.
Photometric information of Messier 21
The following table lists the magnitude of Messier 21 in different bands of the electomagnetic spectrum (when available), from the B band (445nm wavelength, corresponding to the Blue color), to the V band ( 551nm wavelength, corresponding to Green/Yellow color), to the J, H, K bands (corresponding to 1220nm, 1630nm, 2190nm wavelengths respectively, which are colors not visible to the human eye).
For more information about photometry in astronomy, check the photometric system article on Wikipedia.
Apparent size of Messier 21The following table reports Messier 21 apparent angular size. The green area displayed on top of the DSS2 image of Messier 21 is a visual representation of it.
Digitized Sky Survey image of Messier 21
The image below is a photograph of Messier 21 from the Digitized Sky Survey 2 (DSS2 - see the credits section) taken in the red channel. The area of sky represented in the image is 0.5x0.5 degrees (30x30 arcmins).
Celestial coordinates and finder chart of Messier 21
Celestial coordinates for the J2000 equinox of Messier 21 are provided in the following table:
The simplified sky charts below show the position of Messier 21 in the sky. The first chart has a field of view of 60° while the second one has a field of view of 10°.