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Pinwheel Galaxy

Approximately twice the size of our Milky Way, the Pinwheel Galaxy is estimated to contain a trillion stars, 100 billion of them sun-like. This image is composed of 51 individual Hubble exposures. The sharp image shows stunning features in the galaxy's face-on disk of stars and dust along with background galaxies.

Credit: NASA, ESA, K. Kuntz (JHU), F. Bresolin (University of Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (University of Illinois, Urbana), and STScI

Finder Chart for M101
Finder chart for M101
Move the scrollbars to each center or click to enlarge.
Chart: Requio SkyAtlas for Android


The "Pinwheel Galaxy" is registered as "M101" in Charles Messier's catalog of 110 beautiful celestial objects. Its shape is what most people accept as a galaxy, namely a spiral. Relative to Earth, M101 is positioned face-on in that we are looking onto it. It resembles our own galaxy in shape but is nearly twice the size (170,000 light-years across) and lies beyond 21 million light-years away in the constellation of Ursa Major, the Great Bear. In its full entity the galaxy spans over an angular sky area of approximately the size of the full moon, but is only 8.2 magnitudes bright, in other words, not visible to the naked eye.

On August 24, 2011, something spectacular in astronomy happened in the outer region of the Pinwheel Galaxy. A supernova, a star explosion, has been detected where there was nothing before but faint stars. At discovery the nova, dubbed SN 2011fe, was 17.2 magnitudes bright.

First spectroscopic measurements indicated a type Ia nova at its early stage. Scientists expect the nova to reach a maximum visual brightness of 10mv, one of the brightest and closest star explosions in the last decades. It is of special interest to astronomers because the nova may help find clues on the expansion of the universe, thus on the nature of dark energy, which is still a mystery to science. This nova has been detected in its earliest formation and evolution and is so close by as to allow to study this event in unprecedented detail.

At magnitude 10mv, SN 2011fe is visible in binoculars and smaller telescopes appearing like a bright star in the outer region of the galaxy but will lose intensity in due course of its further development. Move your scope or binoculars above the handle of the Big Dipper to the left of Mizar. Resolution of the spiral structure requires a telescope with fairly large aperture, dark skies, and a low power eyepiece.

Remember, the star explosion occurred over 21 million years ago - when mammals flourished and the Mastodon first appeared on Earth - yet one of the closest novae observed since 1986.

Images for the animation courtesy Peter Nugent and the Palomar Transient Factory

Position of SN 2011fe: RA = 14:03:05.81 Dec = +54:16:25.4 (J2000)
Catalogs: Pinwheel Galaxy, M 101, NGC 5457
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