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| NGC 6544 | |
|---|---|
 NGC 6544 imaged by theHubble Space Telescope | |
| Observation data (J2000epoch) | |
| Constellation | Sagittarius |
| Right ascension | 18h 07m 21s |
| Declination | −24° 59′ 50″ |
| Distance | 9450 light years |
| Apparent magnitude(V) | 9 |
| Apparent dimensions(V) | 1' |
| Physical characteristics | |
| Other designations | Cr 366, GCl 87[1] |
| See also:Globular cluster,List of globular clusters | |
NGC 6544 is a smallglobular cluster visible in the constellationSagittarius. It is magnitude 7.5, diameter 1 arcminute. It is less than 1 degree southeast ofMessier 8, the Lagoon Nebula.
NGC 6544 is located in the western part of the constellation, on the edge of a rich star field; its location is easily recoverable as it is located just 50' towards the southeast compared to the famousLagoon Nebula. It can also be seen with 10×50mmbinoculars as a small white spot like a misty star; with atelescope of 120mm and 100× magnification a few small stars may be resolved. Telescopes from 200mm up allow resolving of dozens of dim stars.
Because itsdeclination is rather southern, this cluster can be mainly observed by observers located in theSouthern Hemisphere, although it is still observable even up to medium temperate latitudes. The best time for observation in the evening sky is between June and October.
NGC 6544 was observed for the first time byWilliam Herschel in 1784,[2] who looked at it through his 18.4 inch reflector; he described it as a fairly bright and large object, circular and resolvable into stars; theNew General Catalogue provides a similar description.
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NGC 6544 is a globular cluster of medium density, estimated value of 5 on a scale between 1 and 12[clarification needed]. Its distance is estimated at 2900parsecs (9450light years) from theSun, which in its position corresponds to a distance of 6100 parsecs from the center of theMilky Way and only 100 parsecs from thegalactic plane, making it one of the closest globular clusters to the galactic plane known. Its small angular size, equal to just under 4' for the main body volume and corresponding to just 3.2 parsecs, makes it also one of the smaller globular clusters known.
NGC 6544 has aprograde orbit around the Milky Way, but its orbit is otherwise unusual, and it has a highproper motion. It is unclear whether it formed with the Milky Way or came from elsewhere. In 2021, a low-luminosity globular cluster, namedVVV CL160, was discovered with a similar location, metallicity, and trajectory. It may be associated with NGC 6544.[3]
In 1999 amillisecond pulsar in abinary system was discovered within the cluster and cataloged as PSR J1807-2459.[4] There are a few notablevariable stars that part of NGC 6544; a 1993 study focused on the region around NGC 6544 has identified some variable stars, of which only one is found to belong in storage: it is aRR Lyrae variable with a period of 0.57 days.
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