Messier 101 (Ursa Major)
Fig. 1 - Nearly twice the diameter of our Milky Way: The spiral galaxy Messier 101 in Ursa Major, photographed with a 16-inch f/4.5 Dob on an equatorial platform.
| Object name: | Constellation: | Coordinates: | Apparent size: | Visual brightness: |
|---|---|---|---|---|
| Messier 101 (= NGC 5457) | Ursa Major | 14h03m / +54°21' | 29' x 27' | 7.9 mag |
The intermediate spiral galaxy Messier 101 ("Pinwheel Galaxy", NGC 5457) in the constellation Ursa Major. Messier 101 has a diameter of 252,000 light-years and is approximately 22 million light-years from Earth. The galaxy is about twice the diameter of our own galaxy and is thought to contain about 1 trillion stars. Messier 101 was discovered by French astronomier Pierre Méchain in 1781 (source: Wikipedia).
Exposure time: 5h 26min (107x approx. 3min) at ISO 800, taken on May 4 / 5, 2016, on April 7 / 8, 2018, and on April 16 / 17, 2020. Processing with Deep Sky Stacker and Photoshop. No calibration frames were taken.
Equipment: Canon EOS 450D Baader modified camera, TeleVue Universal Paracorr coma corrector, 16" f/4.5 "Ninja" dobsonian telescope riding on a dual-axis Tom Osypowski equatorial platform, Lacerta MGEN autoguider, Lacerta off axis system.
Field of view comparison: image of the moon with the same setup.
Fig. 2 - Search chart for Messier 101. Copyright 2025 'The Mag-7 Star Atlas Project', www.siaris.net.