Chandra X-ray Observatory
The sharpest X-ray eyes ever flown
Chandra is the third of NASA's Great Observatories — the X-ray complement to Hubble's visible light and Compton's gamma-rays. Its four nested grazing-incidence mirrors are the smoothest large surfaces ever made, focusing X-rays that would punch straight through a normal optic and delivering half-arcsecond imaging that no other X-ray telescope has matched.
Unlike Hubble's low Earth orbit, Chandra was placed into a deeply elliptical 64-hour orbit reaching a third of the way to the Moon. From there it spends most of each orbit above Earth's radiation belts, giving uninterrupted observations of hours-long exposures.
Originally proposed in 1976 and called AXAF, the observatory was renamed in honour of Nobel-laureate astrophysicist Subrahmanyan Chandrasekhar. STS-93 — commanded by Eileen Collins, the first woman to command a Space Shuttle mission — deployed it in July 1999. Twenty-five years on, it is still the most powerful X-ray telescope ever flown.
Mission timeline
- 1976Proposed by Giacconi and Tananbaum
Riccardo Giacconi and Harvey Tananbaum write the first proposal for what becomes AXAF — the future Chandra.
- 1998 · DecRenamed Chandra
AXAF is renamed in honour of Subrahmanyan Chandrasekhar, the Nobel-laureate who first explained the physics of white-dwarf collapse.
- 1999 · Jul 23Launch
STS-93 (Columbia) deploys Chandra on the first Shuttle mission commanded by a woman (Eileen Collins).
- 1999 · AugFirst light
Chandra's first image — a half-arcsecond view of supernova remnant Cassiopeia A revealing a central neutron star nobody knew was there.
- 2002Sgr A* observed
First detailed X-ray observations of the Milky Way's supermassive black hole — including rapid X-ray flares.
- 2006 · Aug 21Bullet Cluster
Chandra's X-ray map of colliding galaxy clusters separated from the gravitational-lensing mass map provides the most direct empirical evidence of dark matter.
- 2018 · OctSafe mode recovery
Gyroscope anomaly triggers safe mode; engineers recover full operation within two weeks.
- 2024 · Jul25th anniversary
Chandra marks 25 years on-orbit — the longest-serving X-ray observatory in history.
- TodayOperating alongside JWST and Hubble
Continues observing AGN, supernova remnants, galaxy clusters, and high-energy phenomena complementing optical and infrared programs.
Active instruments
- Advanced CCD Imaging Spectrometer
X-ray imaging plus per-pixel spectroscopy — Chandra's most-used instrument
- High Resolution Camera
Microchannel-plate detector for the sharpest possible imaging and high-time-resolution observations
- High Energy Transmission Grating
Diffraction grating for high-resolution spectroscopy from 0.4 to 10 keV
- Low Energy Transmission Grating
Companion grating for soft X-ray spectroscopy from 0.07 to 0.2 keV
Headline discoveries
Chandra's imaging of the Bullet Cluster — colliding galaxy clusters whose hot gas (X-ray) lags behind their gravitational mass (lensing) — is the strongest empirical evidence dark matter is a real, gravitating substance.
Chandra revealed rapid X-ray flares from the Milky Way's central supermassive black hole — direct evidence of accretion physics at the galactic centre.
Chandra's first-light image found a previously unknown neutron star at the heart of the Cas A supernova remnant — and later measurements of its cooling rate provided the first observational evidence for superfluid neutrons inside a neutron star.
Related videos
Track Chandra in real time
Fly alongside Chandra in NASA's Eyes on the Solar System — a real-time 3D simulation of its long, highly elliptical orbit far above Earth.
Data: NASA/JPL — Eyes on the Solar System
X-ray universe
The Great Observatories
Hubble Space Telescope
Operational35 years above the atmosphere
Compton Gamma Ray Observatory
RetiredThe gamma-ray sky's first long-duration eye
Spitzer Space Telescope
RetiredSixteen years in the infrared