Page 36 - Astronomy - October 2017 USA

SKYTHIS

MONTH MARTIN RATCLIFFE and ALISTER LING describe the Visible to the naked eye
Visible with binoculars

solar system’s changing landscape as it appears in Earth’s sky.

Visible with a telescope
October 2017: Uranus glows brightly

in evening twilight at the end sight — the maximum angle
of the month. The planet then possible. The rings haven’t
shines at magnitude –0.4 and appeared this open since
hangs a couple of degrees high 2003, and they won’t approach
in the west-southwest 30 min- this tilt again until 2032.
utes after sunset. The steep angle means
After straining to see our observers will get superb
first two targets, skygazers get views of ring structure. The
some welcome relief with the Cassini Division — the dark
appearance of Saturn. The gap that separates the outer
ringed planet lies 20° above A ring from the brighter
the southwestern horizon at B ring — will be obvious
the end of twilight in early through any scope. And this
October. Although it dips will be a great chance to spot
lower as the month progresses, the Encke Division, a narrow,
it remains conspicuous. Saturn challenging feature near the
shines at magnitude 0.5 A ring’s outer edge.
against the backdrop of south- If you can tear yourself
ern Ophiuchus. away from the rings, Saturn
The planet drifts slowly also boasts a family of bright
eastward relative to these moons. The biggest and
background stars, beginning brightest, 8th-magnitude
October 3° north-northeast Titan, completes a circuit of
Earth-based telescopes easily show Uranus’ distinctive blue-green color.
This 2006 Hubble Space Telescope image also reveals banding in the of 3rd-magnitude Theta (θ) the planet once every 16 days.
atmosphere as well as a rare transit by the planet’s moon Ariel (the white Ophiuchi and ending the Look for it due south of
dot) and its shadow (to the right). NASA/ESA/L. SROMOVSKY (UNIVERSITY OF WISCONSIN–MADISON) month 4° northeast of this star. Saturn on October 5 and 21
Now swing your telescope and due north on the 13th and
he giant worlds of the chance to see Jupiter in the to Saturn. The planet’s disk 29th. It appears 1.2' from the
outer solar system take evening sky this year. Those appears 16" across, and the ringed world on those dates.
center stage on October with a clear, unobstructed rings span 36" in mid-October. Outermost Iapetus glows
evenings. While Jupiter western horizon can find the But more significantly, the ring at 10th magnitude when it
Thangs low in twilight, giant planet 3° high a half- system tilts 27.0° to our line of reaches greatest western
Saturn stands higher in a hour after sunset. Fortunately,
dark sky. The more distant it’s bright — shining at mag- Uranus swims with the Fish
world should look spectacular nitude –1.7 — so you can
because its rings open wider track it nearly to the horizon N
than they’ve been in 14 years. despite the bright twilight.
PISCES
But the stars of the evening Jupiter dips lower each
show lie even farther afield. evening and finally suc- /
Neptune grabs the spotlight cumbs to the Sun’s glare ARIES
October 5/6 when its largest after October’s first week. It
moon, Triton, dramatically passes behind the Sun on the
cuts off the light of a distant 26th and will reappear before k Uranus
E
sun. And Uranus reaches oppo- dawn in early November.
sition and peak visibility this Mercury plies nearly the c
month, making it a tempting same parcel of real estate as
target all night. As this planet Jupiter. The innermost planet
sinks low in the west before slides behind the Sun at supe- +
dawn, Venus and Mars make rior conjunction October 8.
1°
a striking pair in the east. Viewers in the southern i
Early October provides United States and points Uranus reaches magnitude 5.7 at opposition October 19. It then lies among
observers with their final south might glimpse Mercury the background stars of Pisces the Fish. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY

36 ASTRONOMY • OCTOBER 2017