Supernova remnant

Cassiopeia A

Also Cas A · 3C 461 · SNR G111.7-02.1

The expanding debris of a massive star whose explosion light reached Earth around 1680.

Measured

About 11,000 light-years. To cross it:

Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.

Its expansion dates the explosion, as seen from Earth, to about 1681, give or take 19 years.
No clear historical record of the supernova survives, perhaps because dust dimmed it.
It is the brightest radio source in the sky beyond the Solar System at frequencies above 1 GHz.
The Chandra X-ray telescope spotted its central compact source, a neutron star, in its first-light image in 1999.

Every catalogue Ouranos draws is credited on the credits page.

Supernova remnant

Also Cas A · 3C 461 · SNR G111.7-02.1

The expanding debris of a massive star whose explosion light reached Earth around 1680.

About 11,000 light-years. To cross it:

Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.

Its expansion dates the explosion, as seen from Earth, to about 1681, give or take 19 years.
No clear historical record of the supernova survives, perhaps because dust dimmed it.
It is the brightest radio source in the sky beyond the Solar System at frequencies above 1 GHz.
The Chandra X-ray telescope spotted its central compact source, a neutron star, in its first-light image in 1999.

Every catalogue Ouranos draws is credited on the credits page.