Astronomy - USA (2020-08)

North Polar Region

North Temperate Zone

North Temperate Belt

North Tropical Zone

North Equatorial Belt

Equatorial Zone

South Equatorial Belt

Great Red Spot

South Temperate Belt

South Tropical Zone

South Polar Region

S

N

South Temperate Zone

WWW.ASTRONOMY.COM 57

their best

just 0.1 magnitude brighter

than Mars during its July

2018 opposition. (The Red

Planet was then sighted by

several people without optical

aid.) Observers have spotted

a dimmer Jupiter in the day-

time as well. In August and

September 1917, F. Sargent of

Bristol, England, followed the

planet in the daylight sky for

more than an hour when the

planet glowed at magnitudes

–2.1 and –2.3, respectively.

Close to opposition, when

Jupiter is at its highest in the

southern sky, keen-eyed

observers will also have their

best opportunity to search for

at least one of the planet’s four

Galilean moons without opti-

cal aid. On the evenings of

July 13 and 14 between the

hours of 3 and 5 Universal

Time (UT), Callisto will be at

its greatest western elongation

from Jupiter — the prime

time to look for the moon.

Jupiter and the

witching hour

To get the most out of observ-

ing Jupiter at opposition,

concentrate on the midnight

hour, when the planet appears

highest in the sky and its

detail is most rewarding. And

no planet shows more detail

than Jupiter, especially when

observing with powers up to

75x per inch of aperture. This

July, Jupiter’s disk measures

48" across, only 2.1" less than

its maximum apparent size.

Fine details then will be near

their best.

Although all of Jupiter is

worth monitoring, observers

have of late been keeping

watch on several recently

active regions. Jupiter’s trade-

mark Great Red Spot (GRS)

especially bears watching.

Most notably, since 2017,

slivers of red material have

been observed peeling off the

spot, distorting its familiar

oval appearance, usually with

extensions described as f lakes,

blades, and hooks. While it’s

not unusual for the GRS to

pull in material or slough it

off, the magnitude of these

recent events has been great

enough to make them visible

in a 3-inch refractor at 200x

(in June 2019).

The GRS has significantly

A combination of wind speed, wind direction, atmospheric jets, and cloud

composition causes Jupiter’s banded appearance. NASA/JPL/SPACE SCIENCE INSTITUTE

On November 1, 1880, French astronomer Étienne Léopold Trouvelot

recorded a stretch of white clouds in Jupiter’s South Equatorial Belt. Could

this have been an SEB disturbance? Also note the fantastic extent of the

Great Red Spot, which has been shrinking ever since. WIKICOMMONS

JUPITER CLOUD FEATURES