Sky and Telescope - September 2018 - 50

SEPTEMBER 2018 OBSERVING
Celestial Calendar

EARLY ON THE MORNING of September
16th, the 11.8-magnitude asteroid 80
Sappho hides a 7.2-magnitude star in
Taurus. The A2-type star, HD 33864 (HIP
24403), lies in the region of the Bull's
horns, about 5½° from Zeta (ζ) Tauri.
Asteroid 80 Sappho is one of five
small bodies detected by British astronomer Norman Pogson from the Madras
Observatory in the latter half of the
19th century. Spotted on May 2, 1864,
the asteroid was named on the advice of
John Herschel, who thought Sappho was
"a suitable name for a small planet."
Spectroscopic studies indicate Sappho
is an S-type Main Belt asteroid, with a
silicaceous, or stony, composition.
The predicted path of visibility
crosses North America from Central
California to Maine. The 4.6-magnitude
drop in brightness is predicted to occur
within a minute or two of 8:48 UT for
Sacramento and Salt Lake City (1:48
a.m. PDT and 2:48 a.m. MDT, respec-

tively), 8:49 UT (3:49 a.m. CDT) for
Sioux Falls, and 8:51 UT (4:51 a.m. EDT)
for Peterborough, Ontario, and Augusta,
Maine. The involved star shines reasonably high in the sky at these times,
though it's lower in the west than the
east (about 25° for California compared
to around 60° for Maine).
Although some photometric measurements of 80 Sappho have been
gathered, data from this event will help
improve the asteroid's shape model.
About a week before the event, more
precise predictions and a path map will
be available from Steve Preston's minor
planet occultation website (asteroidoccultation.com). For more on planning
and setting up your equipment, visit the
International Occultation Timing Association (IOTA) website (occultations.
org). Occultation enthusiasts may also
join an active online discussion group at
groups.yahoo.com/neo/groups/IOTAoccultations.

September Equinox
If the reappearance of the gas giants in the evening sky isn't enough to convince you that summer is over, maybe this will: Astronomically speaking, fall
comes to the Northern Hemisphere on September 23rd at 1:54 UT (September
22nd at 9:54 p.m. EDT), the moment the Sun passes over Earth's equator. This
north-to-south crossing is called the September equinox. On this date, the Sun
rises due east and sets due west from every location on Earth, and should you
be standing on the equator, the Sun would pass exactly overhead at midday.
Thanks to the 23½° tilt of Earth's axis with respect to its orbital plane, the
Sun's highest point in the sky changes depending on the time of year. The tilt
tips one side of Earth or the other toward the Sun as it hurtles around its orbit.
For those of us in the Northern Hemisphere, the Sun appears to climb higher
in the sky each day from late December to late June, and drop lower in the sky
from late June to late December. An equinox marks the point when the Sun is
halfway through its up-and-down journey.

50

S E P TE M B E R 2 018 * SK Y & TELESCOPE

q 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).

29
30

18

PERSEUS
38
21

Algol

TRIANGULUM

34

Minima of Algol
Aug.

UT

Sept.

UT

1

19:58

2

8:52

4

16:46

5

5:40

7

13:35

8

2:29

10

10:23

10

23:18

13

7:12

13

20:06

16

4:00

16

16:55

19

0:49

19

13:43

21

21:38

22

10:32

24

18:26

25

7:21

27

15:15

28

4:09

30

12:03

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.

DA MIT / ASTRONO MICA L INSTIT U TE OF THE CH A RLES UNIV ERSIT Y /
JOSEF Dˇ URECH / VOJTEˇ CH SIDORIN

Asteroid Occultation

t Astronomers have created rough
shape models showing the basic
characteristics and shape of 80
Sappho. Refinements to the model
depend on amateur and professional astronomers acquiring more
data for the asteroid.


http://www.asteroidoccultation.com http://www.asteroidoccultation.com http://occultations.org http://occultations.org http://groups.yahoo.com/neo/groups/IOTA-occultations http://groups.yahoo.com/neo/groups/IOTA-occultations http://www.skyandtelescope.com/algol http://www.skyandtelescope.com/algol

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

Contents
Sky and Telescope - September 2018 - Cover1
Sky and Telescope - September 2018 - Cover2
Sky and Telescope - September 2018 - 1
Sky and Telescope - September 2018 - Contents
Sky and Telescope - September 2018 - 3
Sky and Telescope - September 2018 - 4
Sky and Telescope - September 2018 - 5
Sky and Telescope - September 2018 - 6
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Sky and Telescope - September 2018 - Cover3
Sky and Telescope - September 2018 - Cover4
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