Messier 106 (M106) is a bright spiral galaxy roughly 23.5 million light-years away in the northern constellation Canes Venatici. Also catalogued as NGC 4258, it is famous for two “anomalous” spiral arms, a supermassive black hole at its heart, and water megamasers that make it one of the most precisely measured galaxies in the universe. At apparent magnitude 8.4 it is bright enough to reveal itself in a modest backyard telescope, which is exactly why it has become a favourite spring target for deep-sky observers and astrophotographers alike.
I have spent the better part of two decades photographing galaxies through everything from a small refractor to a remote Ritchey–Chrétien rig, and M106 is one of the handful I recommend to anyone moving up from nebulae to galaxy imaging. It is large, structured, and forgiving — and it shares its field with a clutch of fainter galaxies that turn a single frame into a small treasure hunt. This guide covers what Messier 106 actually is, the science that makes it special, and exactly how to find and photograph it yourself.
Messier 106 at a Glance
- Object designation: Messier 106 / M106 / NGC 4258
- Type: Intermediate spiral galaxy (SAB(s)bc); Seyfert II active galaxy
- Constellation: Canes Venatici (the Hunting Dogs)
- Distance: ~23.5 million light-years
- Apparent magnitude: ~8.4
- Apparent size: ~18.6 × 7.2 arcminutes
- Actual diameter: ~135,000 light-years (slightly larger than the Milky Way)
- Right ascension / declination: 12h 18m 58s / +47° 18′
- Discovered by: Pierre Méchain, 1781
- Central black hole: ~39 million solar masses
What Is Messier 106?
Messier 106 is an intermediate spiral galaxy — a system whose arms wind out from a slightly elongated central bulge rather than a sharply defined bar. Like the Milky Way, it is a flattened, rotating disk of hundreds of billions of stars, threaded with lanes of gas and dust where new stars are born. Tucked into the small constellation of Canes Venatici, just south of the handle of the Big Dipper, it is the brightest member of a loose collection of galaxies sometimes called the M106 Group.
What lifts M106 out of the ordinary is what is happening at its centre. It is an “active” galaxy: its core pours out far more energy than starlight alone can explain, powered by matter spiralling into a supermassive black hole. That activity has left visible scars across the galaxy’s disk — the famous anomalous arms — and has handed astronomers one of their most valuable cosmic measuring sticks. If you want to understand how galaxies grow and how we gauge distances across the universe, M106 is a textbook case you can actually see for yourself.
Discovery and Naming
M106 was discovered in 1781 by the French astronomer Pierre Méchain, a close colleague of Charles Messier. Curiously, it did not appear in Messier’s own published catalogue during his lifetime. Méchain found several objects — including what we now call M105, M106 and M107 — that were never formally added to the list. It was not until 1947 that the Canadian astronomer Helen Sawyer Hogg added them, giving the galaxy the Messier number we use today. Its other label, NGC 4258, comes from the later New General Catalogue compiled by John Louis Emil Dreyer.
This double identity trips up a lot of beginners searching star charts and planetarium apps: “Messier 106,” “M106” and “NGC 4258” are three names for exactly the same galaxy. If your software only recognises NGC numbers, type 4258 and you will land in the right place.
Structure: The Mystery of the Anomalous Arms
Most spiral galaxies show two main arms traced by bright young stars. M106 has those — but it also has a second, ghostly pair that show up most clearly in radio and X-ray light rather than visible starlight. These are the so-called anomalous arms, and for decades they were a genuine puzzle. They are not made of stars at all.
The leading explanation is that the anomalous arms are streams of hot gas being heated and shocked by powerful jets erupting from the galaxy’s central black hole. As the jets plough into the surrounding disk at an angle, they sweep up gas, heat it to millions of degrees, and carve out the glowing structures we detect. In other words, the anomalous arms are the visible exhaust of an actively feeding black hole. They are a vivid reminder that a galaxy’s core can reshape the entire system around it — a process closely tied to where and how new stars form in the disk.
The Supermassive Black Hole and a Cosmic Yardstick
At the centre of Messier 106 sits a supermassive black hole of roughly 39 million solar masses — about ten times heavier than the one at the heart of the Milky Way. What makes this particular black hole special is not its size but how precisely we have weighed it. The gas swirling in toward it forms a thin, tilted accretion disk, and embedded in that disk are clouds of water molecules acting as natural microwave lasers, called megamasers.
By tracking the radio emission from these megamasers, astronomers can map the orbiting gas with extraordinary accuracy and measure the galaxy’s distance using pure geometry — no assumptions about brightness required. That geometric distance, around 23.5 million light-years, has turned M106 into an anchor point for the “cosmic distance ladder,” the chain of measurements astronomers use to gauge the scale and expansion rate of the universe. A galaxy you can spot in a backyard scope is, quite literally, helping to pin down the Hubble constant. For more on the instrument that revealed much of this detail, NASA’s Hubble Messier 106 page is an excellent reference.
How to Find Messier 106 in the Night Sky
The good news for observers is that M106 sits in an easy part of the sky. It rides high for Northern Hemisphere viewers and is best placed on spring evenings, roughly February through May, when Canes Venatici climbs overhead after dark.
The simplest way to find it is to star-hop from the Big Dipper. Locate Phecda (Gamma Ursae Majoris), the bottom-inner star of the Dipper’s bowl, then look toward Cor Caroli, the brightest star in Canes Venatici. Messier 106 lies a little less than halfway along that line. Under a dark sky it is visible as a faint oval smudge in binoculars; a 4-inch telescope shows the bright core, and a 6- to 8-inch scope begins to hint at the elongated halo. As always, darker skies make an enormous difference — a galaxy this faint rewards anyone willing to escape the worst of light pollution.
How to Photograph Messier 106
This is where M106 really shines. It is large and bright enough to image well from typical backyard equipment, yet detailed enough to keep improving as you add aperture, focal length and integration time. Here is how I approach it.
Focal length and framing. At about 18 arcminutes across, M106 frames beautifully somewhere between 700 mm and 2,000 mm of focal length. Shorter focal lengths capture the galaxy plus its companion NGC 4248 and several faint background galaxies in the same field; longer focal lengths, such as those from a Schmidt-Cassegrain, isolate the spiral structure and dust lanes. Before a session, it is worth checking how the galaxy will sit on your sensor with a telescope field of view calculator so you do not crop the fainter outer arms.
Exposure and the dynamic-range trap. M106 has a deceptively bright core and much fainter outer arms, so it is easy to blow out the centre while chasing the halo. I shoot a mix of moderate sub-exposures to protect the core and stack several hours of total integration to dig out the faint structure. A one-shot-colour camera works perfectly well; a monochrome camera with LRGB filters yields the sharpest result, and a touch of hydrogen-alpha brings out the pink star-forming regions along the arms. Getting your sampling right matters here too, so it is worth understanding pixel scale before you commit to a camera-and-scope pairing.
One practical note on location. At +47° declination, M106 is firmly a Northern Hemisphere object. From my own remote setup in the Southern Hemisphere it never climbs high enough to image cleanly, which is a useful reminder that declination, not just magnitude, decides whether a target is realistic from your site. If you are north of the equator, you are in the sweet spot. If you are newer to galaxy imaging in general, our guide to deep-sky astrophotography fundamentals covers the calibration and stacking workflow that makes the difference between a noisy blob and a crisp spiral.
What Else Is in the Field: NGC 4248 and Friends
One of the quiet joys of imaging Messier 106 is everything else that comes along for free. Just to the west of the galaxy sits NGC 4248, a small, ragged-looking galaxy that drifts into almost any wide-enough frame. Scattered across the same field are a handful of fainter, more distant galaxies — among them NGC 4231, NGC 4232 and several anonymous smudges that only emerge once you have stacked a few hours of data.
For visual observers these companions are a challenge reserved for larger apertures and genuinely dark skies, but for astrophotographers they are a gift. I always tell people to resist cropping too tightly: leave some room around M106 and you will be surprised how many island universes are hiding in the background, each one tens or hundreds of millions of light-years away. It is worth pushing your total integration time specifically to bring these faint companions out of the noise — an extra hour or two of data is often the difference between a clean galaxy portrait and a layered map of the deep sky. That small habit is a big part of why M106 stays on my recommended list for anyone learning to process galaxy fields.
Messier 106 vs the Milky Way
M106 is a useful galaxy to compare with our own. At roughly 135,000 light-years across it is slightly larger than the Milky Way’s ~100,000 light-year disk, and both are spiral systems with central bulges and dust-laced arms. The decisive difference is activity: the Milky Way’s central black hole, Sagittarius A*, is currently quiet, while M106’s is actively feeding and driving jets through the disk. Looking at M106 is, in a sense, a glimpse of how our own galaxy’s core may have behaved in more turbulent epochs of its past.
Frequently Asked Questions
How far away is Messier 106?
Messier 106 lies about 23.5 million light-years from Earth. Because its distance was measured geometrically using water megamasers in its core, it is one of the most accurately measured galaxies known.
Can you see M106 with a telescope?
Yes. At magnitude 8.4, M106 is visible as a faint smudge in binoculars under dark skies, shows its bright core in a 4-inch telescope, and reveals its elongated halo in a 6- to 8-inch scope. Darker skies dramatically improve the view.
What constellation is Messier 106 in?
Messier 106 is in Canes Venatici, the Hunting Dogs, just south of the handle of the Big Dipper. You can find it by star-hopping from Phecda toward the star Cor Caroli.
Why does Messier 106 have anomalous arms?
Its two anomalous arms are streams of hot gas, not stars. They are thought to be heated and shaped by jets from the galaxy’s central supermassive black hole ploughing into the surrounding disk.
What is the best time of year to see M106?
For Northern Hemisphere observers, M106 is best placed on spring evenings from roughly February to May, when Canes Venatici rises high in the sky after dark.
Final Thoughts
Messier 106 is the rare deep-sky object that works on every level: an easy spring target for a first telescope, a rewarding and detailed subject for astrophotography, and a genuinely important galaxy for cutting-edge science. Whether you are tracing its faint halo through an eyepiece or stacking hours of data to pull out its dust lanes, you are looking at a galaxy that helps measure the universe itself. Add it to your spring observing list — and when you are ready, point a camera at it. It rarely disappoints. For more objects like it, start with our guide to the full Messier catalogue.
