Galaxy Types Explorer
Explore four major galaxy shapes. Click any card to see an animated view with mass range, star-formation rate, and a real-world example. Use Compare mode to examine two types side by side.
Click a galaxy type above to explore it in detail.
Reference Guide
The Hubble sequence
Edwin Hubble introduced a galaxy classification scheme in the 1920s, often called the "tuning fork" diagram. On the left handle sit ellipticals (E0 to E7, from round to elongated). The fork splits into normal spirals (Sa-Sd) and barred spirals (SBa-SBd). Irregular galaxies fall outside the fork entirely.
A common misconception is that the sequence shows evolution over time. Astronomers now know galaxies do not simply transform from one Hubble type to another as they age.
Spiral arm formation
Spiral arms are density waves, not fixed structures rotating with the galaxy. Stars and gas clouds pass through the arms the way cars slow down at a traffic jam. The increased density triggers new star formation, lighting up the arms with bright young blue stars.
The Milky Way's own arms were mapped indirectly using radio observations of hydrogen gas because dust blocks visible light across the galactic disk.
Star formation rates
Spiral and irregular galaxies still hold large reserves of cold gas and dust, the raw material for new stars. Elliptical galaxies have largely exhausted this supply, which is why they appear red-orange with mostly old, cool stars.
The Milky Way forms roughly one to two new stars per year. The most active starburst galaxies can form hundreds of solar masses of stars every year for a short period.
NGSS alignment
This tool supports performance expectation MS-ESS1-2: Develop and use a model to describe the role of gravity in the motions within galaxies and the solar system. Students examine how galaxy shape relates to stellar age, mass, and ongoing star formation.
Upper elementary students can use the tool as an introduction to classifying objects by observable properties, connecting to NGSS 4-ESS1-1.
