Page 22 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

NORTHERN
EARTH’S AXIS
SPRING EQUINOX
It tilts from the
Day and night are the same length
vertical by 23.5º

THE SUN
APHELION
Earth 152.1 million km
from the Sun
NORTHERN
SUMMER SOLSTICE
The longest day

NORTHERN
AUTUMN EQUINOX
Day and night are
the same length

OUR PLACE

HOW EARTH’S ANNUAL TRIP
EARTH ORBIT ILLUSTRATION BY ADRIAN DEAN, CHARTS BY PETE LAWRENCE
AROUND THE SUN GIVES RISE
IN SPACE TO THE FOUR SEASONS

We take it for granted that Earth is spinning and travels around the makes you think. Standing on the equator, you’ll be travelling at over
Sun. We have to, because there is no way any of us can feel the spin or 1,600km/h (1,000mph).
the speed of movement of our planet as it travels through space.
Cast your mind back to when you were seven years old. You’ve FOUR SEASONS
been told that the reason the Sun crosses the sky is because Earth is Earth’s path around the Sun isn’t all about maximum speeds, though.
turning on its axis once a day. And before you’ve had time to take this Let’s take a look at the seasons. Many think we get spring, summer,
in you’re informed that Earth takes a year to travel round the Sun. autumn and winter because of the distance Earth is from the Sun.
Then, after primary school, you’re introduced to some numbers. Indeed, the Earth does have a slightly elliptical orbit, which leads to
For instance, the average speed of Earth through space (following a distance difference of 5 million km between Earth’s closest point to
its orbit) is just under 30km/s, which is nearly 108,000km/h the Sun (perihelion), and its furthest point (aphelion) – but this doesn’t
(67,000mph). And the rotation of our planet, though slower, still give rise to the seasons. You might be surprised to know that during
22 skyatnightmagazine.com 2012