2019-11-23 New Scientist

(Chris Devlin) #1
23 November 2019 | New Scientist | 51

Next in the series:
1 Mercury transits the sun
2 How to watch the Leonid
meteor shower
3 Venus and Jupiter
in conjunction
4 Mercury at its
greatest elongation
The best time to see
the planet directly
5 How to see the
Northern Lights
6 Find the Andromeda
galaxy
7 How to see Santa (the
ISS) on Christmas Eve


IT ISN’T common to see two
planets in the same part of the sky,
but on 24 November, Jupiter and
Venus will be in what is known as
conjunction. This happens when
their position in space relative to
that of Earth means they appear
to line up.
Most of the time, Venus and
Jupiter are far away from each
other in the sky, but roughly
once a year they line up. The last
conjunction of Venus and Jupiter
happened on 22 January 2019, and
the next will be 11 February 2021.
The two planets will still be on
the opposite side of the sun to
Earth, so they won’t be at their
brightest. But despite Venus being
much smaller – Jupiter’s diameter
is a whopping 140,000 kilometres,
more than 10 times that of Venus,
at about 12,000 kilometres
across – it will appear bigger and
brighter than Jupiter. That’s partly
because it is much closer to us,
and partly down to reflectivity.
The light we see from planets is
all reflected from stars, in this case
the sun. Venus reflects 75 per cent
of the light that hits it thanks to
a thick, permanent cloud layer
containing sulphuric acid. It makes
Venus the second most reflective
object in our solar system after
Saturn’s moon Enceladus. Jupiter’s
atmosphere of water, ammonia
and other gases reflects only
34 per cent of the sun’s light.
At conjunction, Venus passes
just 1.4 degrees from Jupiter in
the sky. As a general idea for the
separation you should expect to
see, this is about three times the
width of the moon. The planets

will stay in conjunction for a
few days, so if it is cloudy on
24 November, you can still see
them together on another day,
albeit slightly further apart.
To see the planets, go
somewhere with a clear view of the
horizon in the direction the sun is
setting. As we learned a few weeks
ago, planets follow the same line
as the sun, known as the ecliptic.
They will start to appear low in the
sky about 45 minutes after sunset.
If you’re having trouble finding
them, an app can help.
It’s easy to tell the two planets
apart as Venus will always be
brighter. In the days after the
conjunction, Jupiter will start

to move closer to the sun while
Venus will appear higher up,
away from the sun.
The planets will set at a time
that depends on your latitude.
For example, at 35 degrees north,
Venus and Jupiter set about 1 hour
and 40 minutes after sunset on 24
November, so you will only have
about an hour to look at them. At
the equator, you will get an extra
10 minutes, while at 35 degrees
south they set 2 hours after sunset.
Use this as an opportunity to
consider how small we are. Venus
and Jupiter are close together
in astronomical terms, but
they are still nearly 700 million
kilometres apart. ❚

This week brings a rare opportunity to see two planets
in conjunction. Abigail Beall explains how to spot them

Puzzles
Cryptic crossword
and a hat-based
logic puzzle p52

Feedback
AI tipping point and
the best new words:
the week in weird p53

Almost the last word
Dogs and nettles,
wasps and waists:
readers respond p54

The Q&A
Geologist Paul Smith
on his love of fossils
and Greenland p56

Twisteddoodles
for New Scientist
A cartoonist’s take
on the world p53

The back pages


PE

TR

HO


LE
K

What you need
A place where you can
see the western horizon


For next week
Binoculars


Abigail Beall is a science writer
in Leeds, UK. This series is
based on her book The Art of
Urban Astronomy @abbybeall


Stargazing at home 2 Week 3


See Venus and Jupiter together


Stargazing at home online
Projects will be posted online each week at
newscientist.com/maker Email: [email protected]
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