Sky and Telescope - October 2018 - 49

October 21
11:30 pm

October
Orionids

TA U R U S

Capella

AURIGA

TWICE A YEAR, barring interference

from weather and moonlight, we get to
see Halley's Comet again - or at least
the bits and pieces it's left in our region
of the solar system. In the spring, we
experience Halley's dusty detritus as
the Eta Aquariid meteor shower, which
occurs when Earth passes through a
trail of dust that's slowly moving outward from the comet's orbit. In October, we see it as the Orionid meteor
shower, when Earth once more encounters a dust stream far from Halley's
path. This year, the predicted peak for
the Orionids falls on the afternoon of
October 21st.
Full Moon is on October 24th, so
peak activity coincides with a waxing gibbous Moon. Even at their best,
Orionid meteors are fast (66 km/s) but
faint. The best viewing for any shower
comes when looking 45°-90° away
from the radiant, and this year some
extra strategizing to avoid moonlight
is in order. Try facing north, with the
Moon at your back. The shower's radiant peaks over the horizon near 10 p.m.
and is highest around 5 a.m. local time.
The diagram at right shows the radiant's location at 11:30 p.m. The Moon is
already high in the south as the radiant
rises in the east.
You may see as many as 20 meteors per hour under ideal conditions,
but expect a number closer to 10. It's
possible that the Orionids operate on a
12-year cycle, with the number of meteors increasing after a point of lesser
activity. The low point was calculated
to fall between 2014 and 2016, so the
number of Orionids per hour may be on
the (slow) rise, on its way to an outburst in or after 2026.
If you see a bright meteor but its path
doesn't seem to track back to a point
of origin in Orion, check to see if it's a
Southern Taurid. Birthed by Comet 2P/
Encke, the Southern Taurids appear to
emanate from a point close to Mu (μ)
Ceti. At the shower's peak on October

Pleiades

Aldebaran

10°

ORION
Orionid
Radiant

GEMINI

Betelgeuse

Castor

Rigel

Pollux

Looking East
p The radiant for the Orionids is located northeast of Betelgeuse. Astronomers once suspected
that the shower had several radiants, each tied to a separate ribbon of dust and each with a different peak date, but recent observations suggest that shower activity is quite stable.

10th, only about 5 Southern Taurids
per hour will spark through the sky.
However, the shower is known for its

ﬁreballs, so it's always worth keeping an
eye open for them on either side of the
peak date.

Minima of Algol
Sept.

Oct.

2
5

8:52
5:40

1
3

0:58
21:47

2:29

18:35

23:18

15:24

Algol

20:06

12:13

16:55

9:02

13:43

5:50

10:32

2:39

7:21

23:28

4:09

20:17

17:05

These geocentric predictions are from the
recent heliocentric elements Min. = JD
2445641.554+ 2.867324E, where E is any
integer. For a comparison-star chart and
more info, see skyandtelescope.com/algol.

PERSEUS
21

TRIANGULUM

p With autumn returning, Perseus is rising into
the northeastern sky. Every 2.7 days, Algol
(Beta Persei) dips from its usual magnitude 2.1
to 3.4 and back. Use this chart to estimate its
brightness with respect to the comparison stars
of magnitude 2.1 (Gamma Andromedae) and
3.4 (Alpha Trianguli).
sk yandtelescope.com * OCTOBE R 2 018

http://www.skyandtelescope.com/algol http://www.skyandtelescope.com

Sky and Telescope - October 2018

Table of Contents for the Digital Edition of Sky and Telescope - October 2018