Sky and Telescope - November 2015 - 45

Learn how to use detailed star charts to ﬁnd the faintest things
that your telescope will show: skypub.com/charts.

Alan MacRobert

Full Moon
Occults Aldebaran

T Cas & Its Partner

At exactly its most annoying phase, plus
or minus just a couple of hours, the
full Moon will occult orange Aldebaran
for Canada and the northern half of
the United States on the morning of
November 26th.
Most full-Moon occultations are
unobservable. Nevertheless, at magnitude +0.9 Aldebaran is the brightest star
that the Moon can ever pass across.
Use high power, and you may be able to
watch it disappear from view like a tiny
orange ﬁre burning on the Moon's limb,
suddenly quenched.
Here are some predicted times (all
a.m.): Boston, disappearance 5:50 EST,
reappearance 6:25 EST. Washington,
DC, d. 5:52, r. 6:32 EST. Toronto, d. 5:41,
r. 6:31 EST. Chicago, d. 4:44, r. 5:28 CST.
Winnipeg, d. 4:22, r. 5:19 CST. Kansas
City, d. 4:54, r. 5:18 CST. Edmonton,
d. 3:01, r. 4:05 MST. Vancouver, d. 1:56,
r. 2:54 PST. Interpolate times between
the two or three cities nearest you.

And the star's average behavior is
changing. For many decades in the midand late 20th century, its cycles displayed
sharp peaks but with the rise halting
partway up and remaining nearly at a
standstill around 9th magnitude before
continuing the rest of the way. Apparently the star is pulsing in a double mode
with two diﬀerent, similar periods that
gradually drift in and out of phase. Such
behavior is not uncommon among Miras.
The neighbor star, HD 1873, is spectral type A0. Its very slight trace of a blue
tinge appears exaggerated by the contrast
with its ruddy companion. The two stars
are unrelated; both lie thousands of lightyears from us.
While you're here, check out the open
clusters plotted around Cassiopeia below.
My favorites are NGC 457 and 7789.

A beautiful example of contrasting star
colors reappears every 15 months when
T Cassiopeiae, especially red even for a
Mira-type variable, rises to its maximum
brightness. At these times it roughly
matches an 8.1-magnitude bluish-white
star 89 arcseconds to its northeast.
Now is such a time. The current maximum of T Cas should last from about
mid-October through November, if the
star behaves as it has during most of its
recent cycles.
T Cas typically varies from visual
magnitude 8.5 to 11.5 and back every
445 days, though it has been reported
as bright as 6.9 and as faint as 13. Its
maximum is unusually long lasting and
nearly ﬂat topped. In most years, anyway.
Sometimes the star quickly rises to a
peak and drops right back.

Just oﬀ Cassiopeia's bright side lie red T Cassiopeiae and its blue-white neighbor. On the wideﬁeld chart below, the black box shows the area of the closeup at right. There, AAVSO comparisonstar magnitudes are given to the nearest tenth with the decimal point omitted.
2h 00m

1h 30m

0h 30m

1h 00m

0h 00m

0h 28m

0h 26m
67

+65°

0h 24m

0h 22m

0h 20m

66
+56° 30′

663
659

CASSIOPEIA
M103

225

Star magnitudes

457

3
4
5
6
7

129

+60°

107

7789

281

_
+55°

Star magnitudes

654

7
8
9
10
11

+56° 00′

104

100
88
+55° 30′

71
84

M76

q
+50°

Sk yandTelescope.com November 2015

http://www.skypub.com/charts http://www.SkyandTelescope.com

Sky and Telescope - November 2015

Table of Contents for the Digital Edition of Sky and Telescope - November 2015