Caldwell 17

Also known as NGC 147, Caldwell 17 is a dwarf galaxy in our local group of galaxies.

Distance

2.5 million light-years

Apparent Magnitude

9.5

constellation

Cassiopeia 

object type

Dwarf Galaxy

Caldwell 17
Also known as NGC 147, Caldwell 17 is a dwarf galaxy in our local group of galaxies.
NASA, ESA, and A. Ferguson (University of Edinburgh, Institute for Astronomy); Processing: Gladys Kober (NASA/Catholic University of America)

Caldwell 17, also known as NGC 147, is a dwarf galaxy located roughly 2.5 million light-years from Earth. It is a member of the Local Group of galaxies, which is dominated by our Milky Way and the Andromeda galaxy. Caldwell 17, like its neighbor Caldwell 18, is a distant satellite of the Andromeda galaxy. Just as the planets in the solar system are gravitationally bound to the Sun, so are these smaller galaxies bound to their much more massive galactic host. While many classes of galaxies can exist as satellites, dwarf spheroidal galaxies (small, dim, spherical-shaped galaxies) like Caldwell 17 have been observed in this role more frequently than any other type of galaxy.

Dwarf satellite galaxies tend to appear very diffuse and dim, so they can be difficult to spot (especially in light-polluted or hazy skies). Caldwell 17 is no exception. It has an apparent magnitude of 9.5, and observers will need a small telescope set up in a dark location to detect the faint galaxy. Caldwell 17 is located in the southern edge of the constellation Cassiopeia, between the constellation’s “W” pattern and the Andromeda galaxy. (The neighboring Caldwell 18 is brighter and less diffuse, so it is easier to see.) The best time of year to spot Caldwell 17 from the Northern Hemisphere is the autumn. It can also be seen in northern latitudes of the Southern Hemisphere in the spring. The galaxy was discovered by the English astronomer John Herschel in September of 1829.

This image of Caldwell 17 is a composite of observations made in visible and infrared light by Hubble’s Wide Field Camera 3. The image captures an area near the core of the galaxy, which is notable for its elderly stellar population. Astronomers used Hubble’s observations to investigate the properties of Caldwell 17’s many globular star clusters.

In the upper right, a ground-based image from the Digitized Sky Survey (DSS) shows Caldwell 17 (NGC 147).
In the upper right, a ground-based image from the Digitized Sky Survey (DSS) shows Caldwell 17 (NGC 147). A white outline near the galaxy’s core defines the area covered in Hubble’s Wide Field Camera 3 (WFC3) image at lower left.
Ground-based image: Digitized Sky Survey; Hubble image: NASA, ESA, and A. Ferguson (University of Edinburgh, Institute for Astronomy); Processing: Gladys Kober (NASA/Catholic University of America)
In the upper right, a ground-based image from the Digitized Sky Survey (DSS) shows Caldwell 17 (NGC 147).
In the upper right, a ground-based image from the Digitized Sky Survey (DSS) shows Caldwell 17 (NGC 147). A white outline near the galaxy’s core shows an area at the center of the galaxy imaged in visible and infrared light by Hubble’s Wide Field and Planetary Camera 2 (WFPC2), shown at lower left.
Ground-based image: Digitized Sky Survey; Hubble image: NASA, ESA, and J. Trauger (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)
Caldwell 17 - 3
In the ground-based Digitized Sky Survey (DSS) image at upper right, a blue outline shows another area of Caldwell 17 (NGC 147) imaged by Hubble’s Wide Field and Planetary Camera 2 (WFPC2) in visible and infrared light. In that Hubble image, shown at lower left, a red square is centered on a globular star cluster in Caldwell 17 that was later imaged by Hubble’s Wide Field Camera 3 (WFC3), also in visible and infrared light (lower right).
Ground-based image: Digitized Sky Survey; Hubble WFPC2 image: NASA, ESA, and J. Trauger (Jet Propulsion Laboratory); Hubble WFC3 image: NASA, ESA, and H. Bond (Pennsylvania State University); Processing: Gladys Kober (NASA/Catholic University of America)
Star chart for Caldwell 17
This star chart for Caldwell 17 represents the view from mid-northern 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.

Dwarf Galaxy - A small, faint galaxy with only millions to a few billion stars.

Globular Cluster - A spherical group of stars that are gravitationally bound to each other, with most of the stars concentrated at the cluster’s center.

Satellite Galaxy - A galaxy that is gravitationally bound to a larger galaxy, much like how the planets in our solar system are gravitationally bound to the Sun.

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.