Printer Friendly

RX and U Cephei.

JUST 7 |Degrees~ FROM POLARIS, and thus visible all night all year, is a 7th-magnitude yellow star known as RX Cephei. It was classified long ago as a semiregular variable with a range of one magnitude. But for nearly a century the star has been poorly observed, and now an astronomer in Hungary is raising the possibility that it may never have varied at all.

RX Cephei is a giant of spectral type G6II and color index +1.1. Three years ago, trusting its description in the General Catalogue of Variable Stars, Endre Zsoldos of Konkoly Observatory included it in an observing program of yellow semiregular variables. He measured its brightness 14 times from September to December 1991; it always held steady at photoelectric V magnitude 7.44.

Checking the literature, Zsoldos realized that most of the published brightness ranges for the star amount to only 0.3 or 0.4 magnitude, suspiciously close to a visual observer's margin of error.

A range of 1.0 magnitude was claimed in the 1880s. However, RX Cephei lies only 1/2 |degree~ from another variable star, U Cephei, an eclipsing binary that drops from magnitude 6.8 to 9.2 every 2.49 days. It's easy to imagine how a change in U might throw off an unwary observer's estimate of RX in the same field of view.

Or maybe the star varies at some times and remains constant at others. You can use binoculars to check RX Cephei whenever the sky is clear.

If history is any guide, you're more likely to spot a change in U. This famous star remains in total eclipse at magnitude 9.2 -- nearly invisible in most binoculars -- for 2.3 hours out of every 60. To help you get lucky, here are the Universal dates and times of its predicted midminima this fall and winter:

September 3, 1:33; 5, 13:23; 8, 1:13; 10, 13:03; 13, 0:53; 15, 12:42; 18, 0:32; 20, 12:22; 23, 0:12; 25, 12:02; 27, 23:52; 30, 11:42;.

October 2, 23:32; 5, 11:21; 7, 23:11; 10, 11:01; 12, 22:51; 15, 10:41; 17, 22:31; 20, 10:21; 22, 22:11; 25, 10:01; 27, 21:51; 30, 9:40.

November 1, 21:30; 4, 9:20; 6, 21:10; 9, 9:00; 11, 20:50; 14, 8:40; 16, 20:30; 19, 8:20; 21, 20:10; 24, 8:00; 26, 19:50; 29, 7:40.

December 1, 19:30; 4, 7:20; 6, 19:10; 9, 7:00; 11, 18:50; 14, 6:40; 16, 18:30; 19, 6:20; 21, 18:10; 24, 6:01; 26, 17:51; 29, 5:41; 31, 17:31.

January 3, 5:21; 5, 17:11; 8, 5:01; 10, 16:51; 13, 4:41; 15, 16:31; 18, 4:22; 20, 16:12; 23, 4:02; 25, 15:52; 28, 3:42; 30, 15:32.

February 2, 3:23; 4, 15:13; 7, 3:03; 9, 14:53; 12, 2:43; 14, 14:33; 17, 2:24; 19, 14:14; 22, 2:04; 24, 13:54; 27, 1:44.

March 1, 13:34; 4, 1:25; 6, 13:15; 9, 1:05; 11, 12:55; 14, 0:45; 16, 12:36; 19, 0:26; 21, 12:16; 24, 0:06; 26, 11:56; 28, 23:46; 31, 11:37.

COPYRIGHT 1993 All rights reserved. This copyrighted material is duplicated by arrangement with Gale and may not be redistributed in any form without written permission from Sky & Telescope Media, LLC.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Celestial Calendar; stars near the constellation Polaris
Publication:Sky & Telescope
Date:Oct 1, 1993
Words:572
Previous Article:Exploring the Moon's south pole.
Next Article:Comet Mueller at the Little Dipper.
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters