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Observing Pinwheel Galaxy (M101)
The Pinwheel Galaxy is a face-on, counterclockwise intermediate spiral galaxy located 21 million light-years from Earth in the constellation Ursa Major. It was discovered by Pierre Méchain in 1781 and was communicated that year to Charles Messier, who verified its position for inclusion in the Messier Catalogue as one of its final entries.
What Pinwheel Galaxy is
The Pinwheel Galaxy is a face-on, counterclockwise intermediate spiral galaxy located 21 million light-years from Earth in the constellation Ursa Major. It was discovered by Pierre Méchain in 1781 and was communicated that year to Charles Messier, who verified its position for inclusion in the Messier Catalogue as one of its final entries.
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 Ursa Major. 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.
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 M 101: The Pinwheel Galaxy, from JPL.
A large spiral galaxy dominates this view from NASA Wide-field Infrared Survey Explorer. The galaxy, often called the Pinwheel galaxy, was designated object 101 in astronomer Charles Messier catalog of fuzzy things in the sky that are not comets.
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 | interacting galaxy |
| Constellation | Ursa Major |
| Apparent magnitude | 7.9 |
| Catalogue | Messier 101 (M101) |
Object data from Wikidata (CC0) and standard Messier catalogues.
What magnification suits M101?
Open the Fit My Telescope toolSee the true field and exit pupil each eyepiece givesFind telescope eyepiece on eBayaffiliateRelated
Sources: Pinwheel Galaxy (Wikipedia, CC BY-SA) · Wikidata (CC0) · NASA Image and Video Library: PIA14403 (public domain)