NGC 6642
| Kugelsternhaufen NGC 6642 | |
|---|---|
 (c) ESA/Hubble & NASA, CC BY 4.0 | |
| Aufnahme des Zentrums durch das Hubble-Weltraumteleskop | |
| AladinLite | |
| Sternbild | Schütze |
| Position Äquinoktium: J2000.0, Epoche: J2000.0 | |
| Rektaszension | 18h 31m 54,2s [1] |
| Deklination | -23° 28′ 34″ [1] |
| Erscheinungsbild | |
| Konzentrationsklasse | IV [2] |
| Helligkeit (visuell) | 8,9 mag [2] |
| Helligkeit (B-Band) | 11,3 mag |
| Winkelausdehnung | 5,8' [2] |
| Farbexzess E(B-V) (Rötung) | 0,42 ± 0,03 |
| Physikalische Daten | |
| Zugehörigkeit | Milchstraße, Bulge |
| Integrierter Spektraltyp | F8 |
| Rotverschiebung | −0,000191 ± 0,000018 |
| Radialgeschwindigkeit | (−57,2 ± 5,4) km/s |
| Entfernung | (23.000 ± 2.000) Lj |
| Kernradius | 6,2″ |
| Gezeitenradius | 10′ |
| Konzentration lg(rt/rc) | ca. 2,0 |
| Geschichte | |
| Entdeckung | Wilhelm Herschel |
| Entdeckungsdatum | 7. August 1784 |
| Katalogbezeichnungen | |
| NGC 6642 • C 1828-235 • GCl 97 • ESO 522-SC32 • Mel 203 • GC 4414 • Cr 381, Bennett 112a, II 205, h 2012, h 3749 | |
NGC 6642 ist ein Kugelsternhaufen im Sternbild Sagittarius auf der Ekliptik. Er hat eine scheinbare Helligkeit von 10,4 mag und einen Winkeldurchmesser von 48″. Der Haufen ist etwa 25.000 Lichtjahre von der Sonne entfernt in Richtung des Zentralbereichs der Milchstraße. Er befindet sich etwa 1 Grad nordwestlich von M 22.[3]
Das Objekt wurde am 7. August 1784 von Wilhelm Herschel entdeckt.[4]
Weblinks
- Standing out from the crowd
- astronews.com: Bild des Tages 12. Dezember 2011
Einzelnachweise
Auf dieser Seite verwendete Medien
(c) ESA/Hubble & NASA, CC BY 4.0
The compact nature of globular clusters is a double-edged sword. On the one hand, having so many stars of a similar age in one bundle gives astronomers insights into the chemical makeup of our galaxy in its early history. But, at the same time, the high density of stars in the cores of globulars also makes it difficult for astronomers to resolve individual stars.
The core of NGC 6642, shown here in this Hubble Space Telescope image, is particularly dense, making this globular a difficult observational target for most telescopes. Furthermore, it occupies a very central position in our galaxy, which means that images inadvertently capture many stars that don’t belong to the cluster — these “field stars” just get in the way.
However, using Hubble’s powerful Advanced Camera for Surveys (ACS), astronomers can identify and remove such distracting field stars, and resolve the cluster’s dense core in unprecedented detail. Using Hubble’s ACS, astronomers have already made many interesting finds about NGC 6642. For example, many “blue stragglers” (stars which seemingly lag behind in their rate of aging) have been spotted in this globular, and it is known to be lacking in low-mass stars.
This picture was created from visible and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys. The field of view is approximately 1.6 by 1.6 arcminutes.