NGC 5897

GCL 33, H VI-8

Globular Cluster

Libra

R.A. 15h17m24.0s

Dec. -21°00'36"

Magnitude: 8.40

Size: 11.0'

Class XI


Given there is no astronomical dark here at 52N now until sometime in August there
are few classes of objects worth going out to have a look at, however globular clusters
are one of them and my choice this week is the globular cluster NGC 5897 in Libra.
Discovered by William Herschel in 1785 NGC 5897 is a quite remote globular lying
about 12550 pc from us ad if at that distance is perhaps 170 light years in diameter.
It is perhaps 7400 pc from the galactic centre. Herschel classified it as part of his
group VI objects so it was a fairly faint compressed group to him. I am always
surprised given how many globular clusters he found that he did not have a separate
group for them as he did for planetary nebulae. It has a concentration class of XI, so
almost as diffuse as it gets. The cluster is classed as metal poor, hence old, although it
would appear to have some younger stars which suggest as second bout of star forming
later on. The two star formation events may have only been separated by a few hundred
million years. The metallicity would suggest an age of perhaps 13 billion years.

ngc5897_pan.jpg

NGG 5897 from PanSTARRS

Interestingly this low metallicity renders the periods of the clusters RR Lyra variables
longer than normal. NGC 5897 is also home to a small number of blue straggler stars.
It is classified as a halo cluster. NGC 5897 is quite large and diffuse so only its core may
be seen from less than optimal locations. It can however been seen with relatively small
telescopes, although may not be resolved with those. The low central concentration and
large radius suggests that NGC 5897 may not have made too many passes through the
galactic plane as it has not suffered from significant tidal evaporation. Perhaps
unsurprisingly NGC 5897 despite its faintness makes many best of observing lists. As it
also lies close to the ecliptic it is occasionally photobombed by planets.

1280px-NGC5897-NRGBhi.jpg

NGC 5897 from Hubble