Sky position, distance and size
Cassiopeia A is placed at J2000 RA 23.4 h, Dec 58.8° at 11,089.3 light-years, with a bright-shell diameter of 13 light-years.
EpochJ2000
Space Time
Supernova remnant · evidence and sources
Cassiopeia A
A young core-collapse remnant about 11,100 light-years away; its light reached Earth roughly 350 years ago.
Also known as Cas A, 3C 461.
Catalog
Position basis, the same label the app shows on the selection card.
Every aspect, with its origin
One record per aspect. The origin says what kind of thing each value is; the source says where it came from; the limit says what it cannot tell you.
ObservedCatalogComputedReconstructedIllustrativeUndocumented
Outer ejecta knots
A representative set of Hammell & Fesen (2008) optical knots is placed at its measured position angle and radius with the measured proper motion. Their line-of-sight depth is not catalogued and is held at zero.
Epoch2004.2 positions; 2004.18 to 2004.93 proper motions
LimitNo radial velocities: the knots are drawn in the sky plane only.
Central compact object offset
The compact object is offset 6.6″ from the optical expansion centre at position angle 174°.
Uncertainty± 1.5″ on the offset.
Adopted distance and size
The model is scaled to a bright-shell diameter of 13 light-years at 11,089.3 light-years, the values published with the source model.
LimitDistance estimates for remnants differ between methods; the page uses the value adopted by the model's authors.
Shock scales and expansion
Forward shock radius 6.5 light-years, reverse shock 4.8 light-years, outer knots to 16.1 light-years at the 2019 reference epoch; the forward shock expands 0.218 % per year (Chandra 2000 to 2019).
Epoch2019; explosion about 1680
MethodProper motions of the X-ray shock fronts scaled with R ∝ t^m.
Published 3D reconstruction
The fly-in shows the published NASA Hubble · Chandra 3D reconstruction mesh, placed at the remnant's sky position and scaled to the listed diameter. It is an authored scientific visualisation built from observations, not a tomographic map of the gas.
LimitThe single-colour source mesh is tinted for legibility; brightness and colour are not calibrated.
What is not measured
- Appearance: a reconstruction from measurements, not a direct observation. Published 3D reconstruction. The single-colour source mesh is tinted for legibility; brightness and colour are not calibrated.
Sources cited
- NASA Hubble · Chandra 3D reconstruction
- Hammell & Fesen (2008) knot catalog (CDS J/ApJS/179/195)
- Thorstensen, Fesen & van den Bergh (2001), expansion centre
- Vink et al. (2022), Chandra shock dynamics
- Cassiopeia A source: nasa model
- Cassiopeia A source: three dimensional structure
- Cassiopeia A source: optical kinematics
- Cassiopeia A source: shock dynamics
- Cassiopeia A source: expansion center
- Cassiopeia A source: knot catalog
- Cassiopeia A source: elements