5 October 2019 | New Scientist | 51Next in the series
1 Model the equinox
2 Find the North Star
and Southern Cross
3 Test your area’s light
pollution
4 Identify the craters
of the moon
See millions of years
of history
5 Orion and Sirius: how
to star-hop
6 Planet spotting: Mars,
Mercury and Uranus
7 Taurus and the zodiacal
constellations
LIGHT pollution makes stargazing
in towns and cities more difficult,
but that doesn’t mean you can’t
see anything. By measuring the
light, you will be able to work
out what you can see in the
best-available conditions and plan
your stargazing trips accordingly.
For this I’m going to use
the constellation Pegasus,
which is visible in the southern
hemisphere between August and
December and in the northern
hemisphere from July to January.
First, pick a clear night with little
moonlight. Then minimise all
light sources. If you live in a city,
find an open green space and go
right to the middle of it. Or, if you
have access to a rooftop, go as high
as possible. If all else fails, your
garden or a high window will do,
just turn off all the lights.
Next you need to give your eyes
time to adjust. If it is really dark,
this could take 40 minutes. If you
are surrounded by lights, you
won’t need this long because
your eyes will only adjust so
much. Bear in mind that the
process is ruined as soon as you
look at a bright light and you will
have to start again.
A star’s brightness as seen from
Earth is known as its magnitude.
This is a logarithmic scale, which
means stars with lower numbers
are brighter. For example, Sirius is
the brightest star in the night sky
and has a magnitude of -1.46, while
the North Star is 1.97. The sun is
-27 and the International Space
Station can reach -6.
To find Pegasus in the north, use
the Plough to find the North Star,as we did last week. Then draw an
imaginary line from any star in the
handle of the Plough, through the
North Star, to get to Cassiopeia –
a distinctive W or M-shaped
constellation. Continue this line
through the Caph star, which is at
one end of Cassiopeia – the right
if it looks like a W to you or the left
if it is an M. This line will take you
to four bright stars – all between
2 and 2.7 magnitude – that make
the Great Square of Pegasus.
In the southern hemisphere,
the easiest way to find the Great
Square at this time of year is to
look due north at around 9pm.
If you’re having difficulty, then
a stargazing app will help.Now count how many stars you
can see inside the square. No stars
means conditions aren’t great. One
star means your visible magnitude
is 4.5, five is 5.25. If you see seven,
you are seeing stars of magnitude
5.5, and 13 stars takes you to 6.
The best you can expect with the
naked eye is 35 stars, which means
you are seeing magnitudes of up
to 6.5, but this only happens in the
darkest skies with no moonlight.
The results depend on your
eyesight, too. But it doesn’t matter
if someone else can see more than
you, just that you know what you
can expect to see. It won’t be a
problem next week, though, since
we will be looking at the moon. ❚You can measure light pollution in your area by counting stars,
says Abigail Beall. You might be surprised by how many you seePuzzles
The crossword, a
puzzle about stamps
and a quick quiz p52Feedback
Letters of note and
rook-y errors: the
week in weird p53Almost the last word
Cycling no-handed
and tidal effects:
readers respond p54The Q&A
Gelong Thubten on
Buddhism, science
and mindfulness p56Twisteddoodles
for New Scientist
A cartoonist’s take
on the world p53The back pages
SERGEI^
MALGAVKO/TASSVI
A^ GET
TYIMAGESWhat you need
A phone with a stargazing app,
but only if you get stuck
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 Week 3
Stars in the city
Stargazing at home online
Projects will be posted online each week at
newscientist.com/maker Email: [email protected]