Sky and Telescope - January 2017 - 49

+30°

TAURUS

+28°
RW
41 Tauri
44 Tauri

Star magnitudes

0.5°

s Tauri

82

3

94

4
5
6
7
8

71

102

+26°

99
RW
Pleiades

+24°

121

+28°
84

p Located 5° northeast of the Pleiades, RW
Tauri drops 3 magnitudes - a factor of 16 in
brightness - in just two hours if you get your
timing right. The black box shows the area of
the closeup chart at right, where comparisonstar magnitudes are given to the nearest tenth
with the decimal point omitted.

41 Tauri

79

52

well-chosen hours, unless you are set up
for imaging and can run an automated
sequence unattended. If you'd just like
to look in on the height of the show
near the edges of totality, when the last
limb of the bright star disappears or
when the first edge peeks back out, you
can detect changes happening visually
in just a few minutes.
Here are predicted mid-eclipse times
until Taurus moves too near the Sun:
November 24, 19:14; 27, 13:41; 30, 8:08.
December 3, 2:35; 5, 21:02; 8, 15:30; 11,

16

Behind
schedule

14
12
10

Mine!

6
4
2
0

Eclipse timings of
RW Tauri,
1887-2014

-2

9:57; 14, 4:24; 16, 22:51; 19, 17:19; 22, 11:46;
25, 6:13; 28, 0:41; 30, 19:08.

January 2, 13:36; 5, 8:03; 8, 2:30; 10, 20:58;
13, 15:25; 16, 9:53; 19, 4:20; 21, 22:48; 24,
17:15; 27, 11:43; 30, 6:10.

February 2, 0:38; 4, 19:05; 7, 13:33; 10,
8:00; 13, 2:28; 15, 20:55; 18, 15:23; 21, 9:50;
24, 4:18; 26, 22:46.

RW Tauri is about 1,000 light-years
away, a distant speck indeed. Running
closely north of it is a faint, slightly
curving line of two stars of magnitudes
12.1 and 12.6. The line is 104″ long.

lobe
che
Ro

Earth

8

Ahead of
schedule

Observed minus calculated time (hours)

better, using CCD-camera photometry.
This method produces timings at least
10 times more accurate thans visual
ones, giving a much higher-resolution
picture of the binary's behavior. The
creeps and jitters in the orbital period
may reveal mass loss and/or mass-swapping - both continuous and abrupt -
or slow, one-way effects of stellar evolution, rotation of the line of apsides, or
the orbital influence of unseen bodies.
Are you up for it? A good timing
requires diligent care for about four

S&T DIAG R A MS: LE A H TISCIONE, SOURCE: PHILLIP A . REED

111

4h 00m

+22°

73

115

B8 V
(primary)

Stre
am

Disk
1900 1920 1940 1960 1980 2000

K0 IV
(secondary)

Size of
Sun

Year

p The payoff. Phillip A. Reed of Kutztown University plotted all 590 known eclipse timings of RW Tauri through November 2014, including the one
I made standing in the snow, as an "O minus C diagram." The observed time of each eclipse is compared to the calculated time when it should
have happened if the period never changed. The difference is plotted on the vertical axis. A change in slope means a change in period. Right: Long
studied, RW Tauri still holds secrets. The dim orange K star fills its surface of gravitational containment (Roche lobe) and overflows to spill an irregular
stream of gas onto the hot, brilliant primary. Surrounding the primary is an intermittent ring of hydrogen, probably splashed up by the infalling stream.
s k y a n d t e l e s c o p e .c o m

* JANUARY 2017

49


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Sky and Telescope - January 2017

Table of Contents for the Digital Edition of Sky and Telescope - January 2017

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Sky and Telescope - January 2017 - Cover1
Sky and Telescope - January 2017 - Cover2
Sky and Telescope - January 2017 - 1
Sky and Telescope - January 2017 - Contents
Sky and Telescope - January 2017 - 3
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Sky and Telescope - January 2017 - Cover3
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Sky and Telescope - January 2017 - SGA17RAL
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