BBC Sky at Night - UK (2021-08)

68 BBC Sky at Night Magazine August 2021

Þ Jupiter’s South

Equatorial Belt

(SEB) vanished

mysteriously in

2010, leaving the

Great Red Spot

to appear as if it

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around the planet

atmosphere is shrouded by a haze layer of ammonia

clouds, making it hard to see detail. Here, visual and

imaging skills need to be honed as much as possible.

One way to accomplish this visually is to make

intensity estimates for different parts of the planet’s

disc and rings (see box, page 71). Also, if you can

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to emphasise subtle features on the edge of visibility.

Atmospheric variations

When we look at Jupiter and Saturn through a

telescope, we’re looking at their atmospheres. Jupiter’s

is most distinctive, appearing as a series of light and

dark banded regions. The famous storm known as the

Great Red Spot (GRS), nestles into a scalloped-out

region on the southern edge of the South Equatorial

Belt (SEB). The atmosphere is rich in shorter-lived

phenomena too, such as light and dark spots, festoons

and barges. In addition, the visibility and appearance

of belts and zones varies over time. In 2010, when the

SEB disappeared completely, the GRS appeared odd

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Saturn has many belts and zones, but they are

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visually or within images. Saturn’s atmosphere does

exhibit intricate detail but thanks to a high haze layer

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out. Bright, light-coloured storms do occur in Saturn’s

atmosphere from time to time. These can become

quite extensive, so it’s important to make accurate

recordings of their estimated size and changes

in shape. Large, long-lived Saturnian storms may

spread until they virtually encircle the globe.

Jupiter and Saturn’s coordinate systems are

equivalent to Earth’s latitude and longitude. However,

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the Greenwich Meridian, Earth’s line of zero longitude.

Latitude is easy: measured in degrees, it varies from

The gravitational pull of the gas

giants inevitably leads to asteroid

impacts. Those large enough to

leave a mark are infrequent,

but several have been

reported and imaged

on Jupiter in recent

years (none have

been reported on

Saturn to date.)

As amateurs

observe and

image the

planets

regularly, they

are the ones most

likely to see and

report such events.

If it’s a big impact

that leaves a

‘scar’, professional

observatories may divert busy

schedules to take a look too.

So it's important to report an

impact site’s location accurately.

It takes experience to make a

visual-only impact claim, but if

the impact has been imaged, it’s

easy to locate using WinJupos’s

measurement scheme

(available for free at

http://jupos.org).

A non-scar

impact typically

appears as a

brief flash.

Impacts may

occur when

you’re looking

away, so post-

capture analysis

with specialist

software, such as

DeTeCt, can help.

If you want to

follow this route

further, look at the Planetary

Virtual Observatory and

Laboratory (PVOL) at http://pvol2.

ehu.eus/psws/jovian_impacts.

Keep an eye out for asteroid strikes on Jupiter

Observing and reporting impacts

Þ Jupiter with an impact scar,

taken on 25 July 2009

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JUPITER

SATURN

Þ South-up views of Jupiter (top) and Saturn (below),

showing the distributions of belts and zones

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