ϑ Ophiuchi

Theta Ophiuchi is Ophiuchus' right foot, as well as being a blue-white subgiant.

Theta is very far to the south; ten degrees south of eta Ophiuchi and three binocular fields east of Antares: binoculars.

One Messier is in this field of view as well as two binaries.

M19 is described in many catalogues as an ‘oblate’ globular, that is, somewhat egg-shaped, a feature easily seen with binoculars. There are apparently about twice as many stars along its major axis as there are on its minor axis.

With an apparent magnitude of 6.8 it is a tiny bright spot composed of 14th magnitude stars. The cluster is easily resolved with higher magnification.

Omicron Ophiuchi is a telescopic binary (H III 25): 5.2, 6.6; 354º, 10.0".

36 Ophiuchi is a multiple system (Sh 243) with some very wide components:
      AB (yellow and red): 5.1, 5.1; 142º, 4.9", orbit of 548.7 years.
      AC: 5.1, 6.5, 74º, 731.6".
      AD: 5.1, 7.8; 338º, 276.5".


Finally, on to the last Messier in Ophiuchus, nearly in Scorpius; with theta Ophiuchi centred move one binocular field southwest; near the southwestern edge will be found M62. M19 is still visible far to the north.

M62 has a much later catalogue number from the other clusters found in Ophiuchus only because Messier took his time cataloguing this one—discovered in 1771 but only measured in 1779. With an apparent magnitude of a bright 6.5, and surrounded by a rich field of stars, it has the appearance of a comet. This irregular shape is due to its proximity with the Galactic Centre, as tidal forces are distorting the cluster; the core, instead of being in its centre, is well seen near one of its edges.

The cluster has a high number of variable stars, at least 89, and the density of its core leads some authorities to suggest it may have undegone a core collapse.

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