New Scientist - USA (2021-02-20)

20 February 2021 | New Scientist | 51

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These articles are

posted each week at

newscientist.com/maker

Abigail Beall is a science writer
in Leeds, UK. She is the author
of The Art of Urban Astronomy
@abbybeall

What you need
Clear night skies
A telescope (optional)
Any good astronomy
app (optional)

OVER the course of a year, the

sun traces a path in the sky. This

invisible line, called the ecliptic,

isn’t created by the sun moving,

but instead by Earth travelling

around the sun.

The solar system’s planets all

orbit in a similar plane to Earth

as it circles the sun – the biggest

difference is Mercury, which

is out by about 7 degrees. This

means they can all be seen along

the ecliptic in the night sky. The

ecliptic is also where the zodiacal

constellations are found and

where eclipses occur, all of which

make it one of astronomy’s most

important features.

The moon doesn’t orbit exactly

on the ecliptic. If it did, we would

have a solar eclipse and a lunar

eclipse every month. Instead,

its orbit is angled at around

5 degrees compared with Earth’s

around the sun. Eclipses occur

when the moon crosses the

ecliptic at a full or new moon.

Even though the planets’ orbits

don’t line up exactly with the orbit

of Earth, they can, like the moon,

generally be used to gauge exactly

where the ecliptic is in the sky.

On any night when you can see a

planet or two and the moon, you

can trace the line of the ecliptic.

At the moment, we can do it by

watching the movement of Mars

and the moon for a few days.

Mars and the moon are in

conjunction on 18 February, with

only 3 degrees separating them in

the sky. This is about the same as

the width of Orion’s belt. After this

date, the two move further and

further apart, largely because of

Want an easy way to locate the planets or find out where an

eclipse is likely to happen? Abigail Beall has the lowdown

Stargazing at home

How to find the ecliptic

the motion of the moon. This

gives us a great opportunity

to look at the ecliptic.

If you want to take part,

pick a time in the 4 or 5 hours

after sunset, not before sunrise.

Try to look at the stars at around

the same time each night for

at least three days between

18 and 27 February.

Once you are set, go out and

search for Mars, which will be in

the south-west in the northern

hemisphere and in the north-west

in the southern hemisphere. It will

be bright with a glowing red hue.

If you are uncertain, use an app to

ensure you have the right target.

Next, find the moon. On

20 February, Mars and the moon

should still be close together. As

the nights go on, the moon will

appear further to the east, and by

the end of^ this period, it will be

low in the eastern horizon just

after sunset. Mars will move much

more gradually, so can be used

to remind you where you saw

the moon on the first evening.

The line that the moon has traced

across the sky over these nights

is the ecliptic.

At the moment, you can only

use the positions of Mars and

the moon in the sky to find the

ecliptic, but you can observe it

on most nights if you can spot

a planet or the moon. During the

day, it is easier to find it, of course:

you just have to watch the sun.

But remember, whatever you

do, don’t look directly at it.  ❚

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