M100 - Mirror Galaxy
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Messier 100, also known as the Mirror Galaxy, is a spiral galaxy with clearly defined arms, located in the constellation Coma Berenices. The object was discovered on March 15, 1781, by the French astronomer Pierre Méchain, and barely a month later, on April 13, 1781, it was entered as the one-hundredth object in Charles Messier’s famous catalog.
M100 is among the most impressive and luminous members of the Virgo Cluster, a concentration of galaxies that forms the dynamical center of the Local Supercluster. This SAB(s)bc spiral galaxy lies at a distance of about 56 million light-years (17.2 megaparsecs) from Earth and has an estimated diameter of roughly 120 thousand light-years, making it comparable in size to our own Milky Way.
Observations
April 25, 2025, around 11:00 PM – Jaworzno, Poland
high level of light pollution
The night was clear, although the sky appeared slightly hazy.
M100’s hallmark is its symmetrical spiral structure, whose well-defined arms host vigorous star-formation regions. The galaxy shows signs of nuclear activity, and its core harbors concentrations of young, hot stars and emission nebulae. Data collected with space telescopes, including Hubble and Spitzer, have enabled astronomers to study its dust, gas, and stellar components in detail.
NGC 4312 is likewise a spiral galaxy, discovered by William Herschel on January 14, 1787. IC 783, by contrast, is a small lenticular galaxy.
These galaxies belong to the Virgo Cluster, which contains more than 1,300 identified galaxies and possibly over 2,000 objects in total. It is the largest and nearest galaxy cluster relative to the Milky Way, forming the core of the entire Local Supercluster.
The galaxies of the Virgo Cluster interact continuously, generating secondary structures such as irregular galaxies, dwarf galaxies, and tidal tails. Radio observations of M100, for example, reveal distortions in the distribution of neutral hydrogen (H I), most likely caused by interactions with the intracluster medium or neighboring galaxies.
Bright and extensively studied, Messier 100 is a rewarding target for amateur observers using medium-aperture telescopes and a vital laboratory for professional astronomers investigating the evolution of galaxies.
April 19, 2026, around 10:30 PM - Katowice, Poland
high level of light pollution
Almost exactly one year after my first observation, I pointed my telescope at M100 once again. This time, the image was captured from Katowice, despite the city’s severe light pollution. Even under the bright urban sky, I was able to capture not only M100 itself, but also a surprising number of much fainter galaxies in the same field of view.
M100 can be seen slightly below the center of the frame. Its disk is seen almost face-on, allowing the bright nucleus and surrounding spiral structure to be clearly distinguished. The galaxy’s two principal arms are especially prominent near the center, while their fainter outer extensions gradually fade into the glow of the light-polluted sky. The irregular features scattered along the arms are star-forming regions containing young stars, gas, and dust.
The wide field of view reveals M100 as part of a much richer galactic environment. At least seven other NGC and IC galaxies can be identified in the image, most of them members of the Virgo Cluster. Although they show up in the photograph as small, faint patches of light, they are in fact enormous systems composed of billions of stars.
Directly below M100 lies NGC 4312, which was already mentioned in connection with the previous observation. It is a spiral galaxy viewed almost perfectly edge-on. Consequently, its spiral arms cannot be seen in the same way as those of M100. Instead of appearing as a nearly circular disk, it takes the form of a narrow, bluish spindle with a brighter central region. The contrast between the two objects clearly demonstrates how strongly a galaxy’s appearance depends on its orientation relative to the observer.
To the right of M100 lies the faint galaxy IC 783, a small lenticular system belonging to the Virgo Cluster. It can be recognized as a subtle, slightly diffuse patch of light, only slightly more extended than a faint star. Detecting such an inconspicuous object against the urban sky provides a good example of what can be achieved by stacking numerous long-exposure frames.
In the upper-left portion of the frame lies the distinctive galaxy pair NGC 4340 and NGC 4350. NGC 4340 is a barred lenticular galaxy in which two nested bars have been identified, together with a ring-like structure composed primarily of older stars. Here, it is visible as a bright, slightly oval patch of light.
Nearby NGC 4350 is also a lenticular galaxy, although its disk is seen much closer to edge-on. This orientation gives it the appearance of a bright spindle with a clearly defined central region. The two galaxies are physically close neighbors within the Virgo Cluster, rather than merely appearing close together in projection.
NGC 4405 can be found on the left-hand side of the photograph. Its small disk is inclined relative to our line of sight, giving it the appearance of a short, bluish ellipse. Farther down lies NGC 4396, another barred spiral galaxy seen nearly edge-on.
NGC 4421 is a barred lenticular galaxy whose disk is viewed at a moderate inclination. In this image, it forms an oval glow with a brighter center. Like the other objects described here, it belongs to the remarkably rich population of galaxies seen toward the constellations of Coma Berenices and Virgo.
This observation demonstrates that M100 is not an isolated object suspended in empty space. It belongs to an extensive galaxy cluster, and the wide field of view captures its immediate cosmic neighborhood within a single frame. The individual galaxies differ in size, morphology, and orientation—from the nearly face-on M100 and the oval lenticular systems to the narrow disks of NGC 4312, NGC 4350, and NGC 4396.
Photo 1 Parameters:
- Total exposure time: 90 minutes (stack of 90 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- ISO: 1600
- Canon EOS 600D
- Maksutov-Cassegrain telescope (100/1400), prime focus exposure
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
Photo 2 Parameters:
- Total exposure time: 120 minutes (stack of 120 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- ISO: 1600
- Canon EOS 600D
- lens: Samyang 800mm MC IF f/8
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system
References:
- Sinnott R. W., The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer, Sky Publishing Corporation, 1988
- Wozniak H., et al., Double-barred starburst galaxies viewed by ISOCAM, The Universe as Seen by ISO, 1999, 427, pp. 989
- Chung A., et al., VLA Imaging of Virgo Spirals in Atomic Gas (VIVA). I. The Atlas and the H I Properties, The Astronomical Journal, 2009, 138(6), pp. 1741-1816
- Sakamoto K., et al., Bar-Driven Gas Structure and Star Formation in the Center of M100, The Astronomical Journal, 1995, 110(3), p. 2075
Marek Ples