Hubble's Messier Catalog

Overview

The Messier catalog, begun by astronomer Charles Messier in the 18th Century and revised over the years, includes some of the most fascinating astronomical objects that can be observed from Earth’s Northern Hemisphere. Among them are deep-sky objects that can be viewed in stunning detail using larger telescopes but are also bright enough to be seen through a small telescope. This characteristic makes Messier objects extremely popular targets for amateur astronomers possessing all levels of experience and equipment. They are so popular, in fact, that they have inspired a special award from the Astronomical League (an organization for amateur astronomers) given to observers who are able to spot each of these objects. Those who succeed receive a certificate and are given the distinction of being in the Messier Club.

As of June 2018, Hubble has observed 96 of the 110 objects in Charles Messier's catalog. Of those observations, 89 were processed into the images below. Some of Hubble's photographs offer views of a given object in its entirety, but many focus on specific areas of interest. While Hubble is able to magnify objects very effectively, it has a relatively small field of view. This means, in some cases, Hubble would need to take many exposures to capture an entire object. Although this is not always an efficient use of its time, as is the case for the widely spaced “open” star clusters in the Messier catalog, many exposures are taken when the scientific value justifies the time spent. One of these objects is the Andromeda galaxy (designated M31 in Messier’s catalog). In order to create a mosaic image of Andromeda, Hubble took thousands exposures of the galaxy over more than ten years

Unlike a digital camera that takes a single photograph in red, green, and blue light to create a single full-color image, Hubble takes monochrome images at specific wavelengths of light. These specific wavelengths reveal characteristics of an object that are of scientific interest, such as the presence of a particular chemical element. Astronomers and image processors combine multiple observations at different wavelengths to form a single image that reveals all of these characteristics at once but doesn’t necessarily contain the full spectrum of visible light. In those cases, image processors assign colors to each wavelength according to their chromatic order that highlights the object's different characteristics, offering us a deeper understanding of its properties.

Additionally, Hubble is equipped to take infrared and ultraviolet images, which can reveal information that astronomers cannot obtain using only visible light. Because the human eye is not sensitive to infrared and ultraviolet light, these observations are processed in a way that makes them meaningful to observers. This is done by assigning colors that humans can perceive to the wavelengths that they cannot.

Whether their tool of choice is a sophisticated ground-based telescope, a decent pair of binoculars, or simply their naked eyes, observers hunting for Messier objects can use the data gathered from Hubble’s spectacular images to deepen their understanding of these 110 highlights of the night sky as they carry on the tradition of amateur astronomy.

The following pages contain some of the best images from Hubble’s Messier catalog taken thus far.