New Scientist - International (2019-11-23)

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

RÁ

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]