Sky and Telescope - September 2018 - 49

Jupiter's Moons
2h 10m

2h 00m

1h 50m

1h 40m

ARIES
Sept 1

Star magnitudes

+12°

Aug 1

4

Pat

July 1

Sept 1

5
6
7
8
9

ho

June 1

2

f Ur

Oct 1

anu

3

s

Europa

Feb 1
Dec 1

+10°

WEST

4

Mar 1
Nov 1

EAST

5
6

Jan 1, 2019

7

PISCES

8

k

9
10

23h 10m

23h 00m

22h 50m

11

Callisto

12

Pat

q

Star magnitudes

June 1
4
5
6
7
8
9

Mar 1

ho

f Ne

July 1
Aug 1

ptu

- 6°

ne

14
15

Feb 1
Jan 1, 2019

Sept 1
Oct 1

r

83

13

16

h

17

Nov 1 Dec 1
- 8°

AQUARIUS

18
19
20

s1

RG-610
filter

21:55 UTC

Ganymede

21

RG-610
filter

21:55 UTC

p Damian Peach captured this image of 3.68″wide Uranus on October 21, 2015, using a
color astronomy camera with an RG-610 longpass filter on a 14-inch Schmidt-Cassegrain.
SEN / DA MIA N PE ACH

Io

Neptune, though the fourth-largest
planet by diameter in our solar system,
is a true telescopic/big bino object,
thanks to its distance from Earth. It
shines at magnitude 7.8 and appears

only 2.4″ wide at opposition. In my
130-mm reflector, it doesn't look much
more than stellar, but the 10-inch can
bring out both form and color, a pale,
pleasing blue. It usually looks more gray
than blue to me, though, especially with
more magnification. The atmospheres
of Neptune and Uranus consist primarily of hydrogen, helium, and methane.
It's this last molecule, CH4, that reflects
light on the blue-green end of the spectrum.
Sometimes it's difficult to convince
yourself that you're seeing what you're
supposed to be seeing. Sketch the
starfield with as much detail as you
can and clearly mark the dot you think
is the planet. Return to the field on
the next clear night and make a fresh
sketch. If your dot has moved to a new
position, you've rediscovered a gas giant.

22
23
24
25
26
27
28
29
30
Oct 1

The wavy lines represent Jupiter's four big satellites. The
central vertical band is Jupiter itself. Each gray or black
horizontal band is one day, from 0 h (upper edge of band)
to 24h UT (GMT). UT dates are at left. Slide a paper's edge
down to your date and time, and read across to see the
satellites' positions east or west of Jupiter.



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
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