Caldwell 89

This distant cluster is visible in binoculars as a blurry patch, and small telescopes can resolve some of its stars.

Distance

3,500 light-years

Apparent Magnitude

5.4

constellation

Norma

object type

Open Cluster

Caldwell 89
This collection of stars captured in infrared light by Hubble’s Wide Field Camera 3 is part of Caldwell 89, also known as NGC 6087. This open cluster consists of approximately 40 stars, the brightest of which (near the center here) is the variable star S Normae.
NASA, ESA, and A. Riess (Johns Hopkins University); Processing: Gladys Kober (NASA/Catholic University of America)

This shining collection of stars captured in infrared light by Hubble’s Wide Field Camera 3 is part of Caldwell 89, also known as NGC 6087. This open cluster consists of approximately 40 stars, the brightest of which (near the center here) is the variable star S Normae.

Caldwell 89
The Digitized Sky Survey (DSS) image in the lower left shows the star cluster Caldwell 89 (NGC 6087) as seen from the ground. The small square in that image shows the field observed by Hubble’s Wide Field Camera 3 (WFC3), which features the relatively bright star S Normae.
Ground-based image: Digitized Sky Survey; Hubble image: NASA, ESA, and A. Riess (Johns Hopkins University); Processing: Gladys Kober (NASA/Catholic University of America)

Cepheid variable stars like S Normae change brightness at a regular and predictable rate. There is also a relationship between a Cepheid’s pulsation rate and its intrinsic brightness. A Cepheid’s pulsation rate tells us how bright it truly is, so how bright it appears to us tells us how far away it is. (The farther a Cepheid is, the dimmer it appears.) This makes Cepheids important “standard candles” for measuring distances in the universe. Hubble’s observations of Caldwell 89 were made to improve the calibration of S Normae as a standard candle.

Caldwell 89 has an apparent magnitude of 5.4 and is located 3,500 light-years away in the constellation Norma. S Normae fluctuates between apparent magnitudes of 6.12 to 6.77 over an approximately 10-day period. The cluster visible in binoculars, and a small telescope can resolve some of its stars. Caldwell 89 is best observed in the Southern Hemisphere’s winter (or in summer for Northern Hemisphere observers close to the equator). It is not far from Caldwell 95 (NGC 6025), another open star cluster that’s about the same size and brightness.

A simple map of the sky shows outlines of constellations, labeled stars, and the location of Caldwell 89
This star chart for Caldwell 89 represents the view from mid-southern latitudes for the given month and time.
Image courtesy of Stellarium

Glossary

Apparent Magnitude - The brightness of an astronomical object as seen from Earth, influenced by the object's distance from Earth, its absolute magnitude, and even gas and dust that lie between the object and Earth.

Cepheid Variable Star - A star that pulses regularly, resulting in observable changes in its brightness; the star’s pulsation rate is related to the star's intrinsic brightness, which makes Cepheids important tools for measuring distances in the universe.

Open Cluster - A group of stars loosely bound by gravity, destined to be short lived because the gravitational interactions between members are weak enough that stars can be drawn away from the cluster by stronger gravitational forces.

Standard Candle - An astronomical object with a known absolute magnitude, allowing astronomers to precisely calculate its distance from Earth by measuring its apparent brightness.

Explore Hubble's Caldwell Catalog

The following pages contain some of Hubble’s best images of Caldwell objects.

Stars with four diffraction spikes dot the scene against a black backdrop.

Caldwell 1

Also known as NGC 188, this group of stars formed from a large cloud of gas making the stars roughly…

Red cloud of dust with a bright white star in the center of it. Lots of reddish and orangish stars in the background.

Caldwell 2

This shell of gas is expanding outward, away from the dying star within.

Large grouping of bright white, blue and red stars. Lightly colored blue dust surrounds the stars.

Caldwell 3

This barred spiral galaxy was first spotted by British astronomer William Herschel in April 1793 in the constellation Draco.