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Messier 100

This grand-design spiral galaxy offers a majestic view through larger backyard telescopes.

Distance

56 million light-years

Apparent Magnitude

10.1

constellation

Coma Berenices

object type

Spiral Galaxy

M100 as seen by Hubble
NASA, ESA, and Judy Schmidt

​Messier 100 (M100) is a stunning example of a grand-design spiral galaxy. This detailed Hubble image reveals individual stars within the galaxy’s prominent spiral arms. These dusty structures swirl around the galaxy’s nucleus and are marked by a flurry of star formation. M100’s characteristic arms also host several small black holes, including the youngest one ever observed in our cosmic neighborhood.

The galaxy was discovered in 1781 by the French astronomer Pierre Méchain, Charles Messier’s fellow comet hunter who discovered eight comets in his lifetime. M100 is located 56 million light-years away from Earth and appears dim in the night sky. Its apparent magnitude of 10.1 means that, while it can be seen through small telescopes, it will appear only as a faint patch of light. Larger telescopes can resolve more details of this galaxy. M100 is located in the constellation Coma Berenices and is best observed during May.

The Spiral Galaxy M100
The image's stair-step appearance results from the design of the camera used to take the exposures. The camera consisted of four light detectors, one of which provided a higher resolution but had a smaller field of view than the other three. Because the detector with the higher resolution does not cover as much area as the others, black regions remain when the images from all four detectors are combined into one picture. The image was taken on December 31, 1993 with Hubble's Wide Field Planetary Camera 2 (WFPC 2). This color picture is a composite of several images taken in different colors of light. Blue corresponds to regions containing hot newborn stars.
NASA, ESA, J. Trauger, JPL

This image above of M100 resolves individual stars within the majestic spiral arms. (These stars typically appeared blurred together when viewed with ground-based telescopes.) Hubble has the ability to resolve individual stars in other galaxies and measure accurately the light from very faint stars. This makes space telescope invaluable for identifying a rare class of pulsating stars, called Cepheid Variable stars embedded within M100's spiral arms. Cepheids are reliable cosmic distance mileposts. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years.

region of M100 highlighting a Cepheid variable star
This Hubble image of a region of M100 shows a type of pulsating star called a Cepheid variable. These stars are reliable distance indicators to galaxies. The top three frames, taken on three different dates in May 1994, reveal that the star (in the center of each box) changes brightness. Cepheids go through these changes rhythmically over a few weeks. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the star’s intrinsic brightness. Astronomers can use this brightness to precisely determine the galaxy’s distance.
Wendy L. Freedman, Observatories of the Carnegie Institution of Washington and NASA

M100 is a rotating system of gas and stars, similar to our own galaxy, the Milky Way. Hubble routinely can view M100 with a level of clarity and sensitivity previously possible only for the very few nearby galaxies that compose our Local Group of galaxies. M100 is a member of the huge Virgo cluster of an estimated 2,500 galaxies. The galaxy can be seen by amateur astronomers as a faint, pinwheel-shaped object in the spring constellation Coma Berenices.

three images of the same galaxy, different resolutions
These three images show the central region of spiral galaxy M100, taken with three generations of cameras aboard Hubble, and document the improving capability of the observatory. The image on the left was taken with the Wide Field and Planetary Camera 1 (WFPC1) in 1993. The photo is blurry due to a flaw (called spherical aberration) in Hubble's primary mirror. Celestial images could not be brought into a single focus. The middle image was taken in late 1993 with the Wide Field and Planetary Camera 2 (WFPC2), installed during the Dec. 2 – 13, 1993, space shuttle servicing mission (SM1, STS-61). The camera contained corrective optics to compensate for the mirror flaw, and so the galaxy snapped into sharp focus when photographed. The image on the right was taken with a newer instrument, the Wide Field Camera 3 (WFC3), installed on Hubble during the space shuttle servicing mission in May 2009.
NASA, ESA, STScI and Judy Schmidt

For more information about Hubble’s observations of M100, see:

locator star chart for M100
This star chart for M100 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium

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