NGC 1901

CALCULATED · NOT AN OBSERVATION · ANGULAR SIZE AT THE CATALOGUED DISTANCE · OPEN CLUSTER · MAJOR AXIS 11.1′ · NO SURFACE — DRAWN AS A VOLUME · MEMBERS DRAWN, NOT COUNTED

A cloud of gas glowing at the lines its class emits, brightest in the middle and fading through the colour of the outer gas. The shape of it is the catalogued class; the flattening is the catalogued axis ratio read as the object's own shape rather than as a tilt, because this is not a disc and its ellipticity is not an inclination. Nothing measured the depth, so what is drawn is the roundest object that matches the ellipse the catalogue holds. Every member is drawn at the one temperature its class implies; how many are drawn is a drawing choice and not a population. 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.

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

05h 18m 08.7s

DECLINATION

−68° 24′ 24.8″

GRID TURNED SINCE J2000

1.9′

PROPER MOTION SINCE J2000

none published

Computed for 2026-10-23 00:00 UT. No proper motion is published for NGC 1901, 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.