HOW BIG
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Pinwheel Galaxy · M101: size, dimension and comparison

The adopted reference is about 170,000 light-years.

diameter of the luminous disc ≈ 170 000 ly

A light-year is a distance: how far light travels in one year. It is used for distances between stars.

A large spiral seen almost face-on.

Explore at this scale
Pinwheel Galaxy · M101, interpreted illustration
Interpreted illustration · dimension stated in the fact sheet.

What does this number measure?

NASA's Hubble catalogue describes a disc spanning 170 000 ly. The diameter concerns the disc of stars, gas and dust; the dark matter halo is not included.

Compare the stated dimensions

The comparison uses the number in each fact sheet: altitude, height, diameter, length or distance, depending on the reference. Two values in metres do not necessarily describe the same property.

Compare with Cartwheel Galaxy in the explorer →

Source and limitations

Rounded documentary extent. Boundaries are diffuse and depend on the observations and convention used; this is not a distance from Earth.

Original schematic illustration, not a photograph. Shapes, colours and details are interpreted; only the stated dimension is compared.

Illustration sources

How Big — generated illustration; NASA/ESA documentation.

Source coverage: Visual interpretation; colours and texture do not constitute an observation. Only the designated extent follows the catalogue's reference value.