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Observing Whirlpool Galaxy (M51)
The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy.
What Whirlpool Galaxy is
The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 31 million light-years away and 23.58 kiloparsecs (76,900 ly) in diameter.
How to observe it
This is a fainter target that rewards aperture and dark skies. A 150 mm or larger telescope from a site away from town lights shows it best, and averted vision helps.
It lies in the constellation Canes Venatici. To find it, learn the constellation first, then star-hop from its brighter stars with a finder or a wide-field eyepiece before switching to more magnification.
Magnification is your telescope's focal length divided by your eyepiece's focal length. For an extended object like this, start low to frame it, then step up in power only if the object takes it. Use the Fit My Telescope tool to see the exact magnification, true field and exit pupil each of your eyepieces gives.
How it looks at the eyepiece
What you see at the eyepiece is fainter and less colourful than a photograph, because the eye takes in light in an instant while a camera builds it up over minutes. Expect a grey glow rather than the vivid colours of an image, and let your eyes dark-adapt for at least twenty minutes to see the most.
This object is a face-on spiral with a companion, the classic small-telescope galaxy, which makes it a rewarding target once you have found it.
Frame it at low to medium power first with a wide true field, then step up the magnification only if the object stays sharp and the sky is steady. The Fit My Telescope tool shows the magnification, true field of view and exit pupil each of your eyepieces gives in your telescope, so you can pick the one that frames the object best.
The object in NASA imagery
NASA has imaged this object. One example in the NASA Image and Video Library is titled Whirlpool Galaxy, from JPL.
The image from NASA Hubble Telescope shows spiral arms and dust clouds in the nearby Whirlpool galaxy. Visible starlight and light from the emission of glowing hydrogen is seen, which is associated with the most luminous young stars in the spiral arms.
NASA imagery is in the public domain. What you see through an eyepiece is fainter and mostly grey, since the eye does not accumulate light the way a long-exposure camera does, but knowing an object's true shape helps you recognise it at the telescope.
| Property | Value |
|---|---|
| Object type | grand design spiral galaxy |
| Constellation | Canes Venatici |
| Apparent magnitude | 8.4 |
| Catalogue | Messier 51 (M51) |
Object data from Wikidata (CC0) and standard Messier catalogues.
What magnification suits M51?
Open the Fit My Telescope toolSee the true field and exit pupil each eyepiece givesFind telescope eyepiece on eBayaffiliateRelated
Sources: Whirlpool Galaxy (Wikipedia, CC BY-SA) · Wikidata (CC0) · NASA Image and Video Library: PIA04230 (public domain)