RY Oct

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

21h 39m 06.8s

DECLINATION

−77° 10′ 59.3″

GRID TURNED SINCE J2000

12.2′

PROPER MOTION SINCE J2000

0.80″

Computed for 2026-10-27 00:00 UT. Two things separate it from the catalogued position above: RY Oct has moved under its own proper motion, and the coordinate grid has turned 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.

RANGE, AS SAMPLED

11.37 – 12.59

PERIOD

0.563469 days (13.5 h)

PHASE

0.336 ± 0.053

NEXT MAXIMUM

2026-10-27 08:58 UT---------- --:-- your time

THEN

2026-10-27 22:30 UT---------- --:-- your time

THEN

2026-10-28 12:01 UT---------- --:-- your time

Computed for 2026-10-27 00:00 UT. A phase of zero is maximum light, and RY Oct was last there 4.5 h before that. The ± is what the published elements can still promise: 59,192 cycles have gone by since the epoch they were measured at, and the last digit of the period compounds over every one of them — 43 min by now. It is the precision of the published figures rather than an error bar the catalogue supplied, so where that catalogue has marked a period doubtful the real spread is wider — and it does not contain the star. A binary with a third body in the system, or a pulsator whose period is slowly changing, walks away from a straight-line ephemeris by an amount only observation settles. Times are corrected for where the Earth is in its orbit, which is worth up to 8.3 minutes — the light of a star reaches us that much earlier in one season than the other, and an epoch measured a century ago has the same correction in it.

The range is the spread the Hipparcos satellite measured, converted to the visual scale. It is approximate: the satellite sampled the star on a schedule of its own, and where a star spends little of its cycle at an extreme — the floor of an eclipse, most obviously — the sampling can miss it altogether. The classification, the period and the epoch are the General Catalogue of Variable Stars’s. The phase at any instant.