Sagittarius A*

CALCULATED · NOT AN OBSERVATION · SCHWARZSCHILD RADIUS FROM THE MASS · 4 300 000 M☉ · ACCRETION HOT FLOW · INCLINATION 30° · SKY BENT AROUND THE HOLE

The black disc is the shadow, 2.6 times wider than the horizon that casts it, and every ray in the frame is a null geodesic of the Schwarzschild metric. Too little gas is falling in for it to cool and settle into a disc, so what is drawn is a thin, hot, transparent flow — brightest where light loops the hole and passes through it twice. Drag it, or use the arrow keys, to look from another direction. The stars behind are the 498,631 this catalogue holds real distances for, drawn from where the camera actually is — but every one of them is within 170 parsecs of the Sun and this object is much further out, so from here that whole neighbourhood is a knot in one direction and the rest of the sky is empty. The view you land on looks the other way; turn back towards the Sun and the stars come with it. What the readout says is which of the two the frame is pointed at. The emptiness is not a missing backdrop — it is the edge of what this catalogue has measured. And they are not where they are. Light that passes a black hole is bent towards it, so every star behind this one is seen further from it than it stands: the ones almost directly behind swing out into a ring and brighten as they go, the sky immediately around the shadow is emptied to fill that ring, and part of the ring is light from stars behind you, carried round the far side. Turn the view and watch a star climb out of the middle rather than cross it. Each one is still a measured parallax — moved along the path the metric gives its light, and nothing else.

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  EHT Saggitarius A black hole

  EHT Collaboration
  CC BY 4.0

Where a telescope has to be pointed today, which is not quite where the catalogue records the object: the coordinate grid itself has turned since the year 2000 the catalogue is referred to.

RIGHT ASCENSION

17h 47m 22.8s

DECLINATION

−29° 01′ 08.0″

GRID TURNED SINCE J2000

22.5′

PROPER MOTION SINCE J2000

none published

Computed for 2026-10-11 00:00 UT. No proper motion is published for Sagittarius A*, so nothing here moves the object; what separates this from the catalogued position above is the coordinate grid turning under it — about fifty arcseconds a year of precession since 2000, and the small nodding of the Earth’s axis on top of that. The catalogue it came from publishes no error for that position, so nothing here says how far this arithmetic can be trusted — the digits above are as precise as the place they were computed from, and no more. Aberration, parallax and refraction are left out. Aberration swings every position by up to twenty arcseconds over a year; parallax stays under an arcsecond for all but the nearest stars; refraction is nothing overhead and about half a degree at the horizon, where it answers to the air, not the sky. The same figure for any date.