The Cartwheel Galaxy
The Cartwheel Galaxy is a lenticular ring galaxy about 500 million light-years away in the constellation Sculptor. Fritz Zwicky, who discovered it in 1941, called it “one of the most complicated structures awaiting its explanation on the basis of stellar dynamics.”
Briefing
The Cartwheel Galaxy (ESO 350-40; PGC 2248) is a lenticular ring galaxy in Sculptor, about 500 million light-years from Earth. It has a D25 isophotal diameter of 57.69 kiloparsecs (188,200 light-years) and a mass of about 2.9–4.8 billion solar masses; its outer ring has a circular velocity of 217 km/s.
How we know
Its quoted physical size is tied to a specific kind of measurement: the Third Reference Catalogue of Bright Galaxies (RC3) measured a D25 isophotal diameter of about 60.9 arcseconds—an angular diameter defined at the D25 isophote, a standard brightness contour used to compare galaxies. Converting that angle into a linear diameter requires a distance; the RC3 value given here uses a redshift-derived distance of 132.2 megaparsecs (431 million light-years), yielding 57.69 kiloparsecs (188,200 light-years).
- Unseen
- No apparent magnitude or observing guidance is provided in the supplied material; nothing here supports a reliable naked-eye or small-telescope viewing note.