The numbers
- Where it points
- Always away from the Sun
- How many tails
- 2one of dust, one of gas
How it happens, step by step
Far from the Sun
The comet is a dark, silent block of ice. It has no coma and no tail, and it is almost impossible to see.
Ice turns to gas
As it gets closer, the heat turns the ice straight into gas. The gas leaves the nucleus and carries dust with it.
The coma is born
Gas and dust form a glowing cloud around the nucleus, much bigger than the nucleus itself: it is the coma.
The Sun pushes
Sunlight and the solar wind push the light particles away from the coma, always away from the Sun.
Two different tails
The dust forms a wide, curved tail, the gas a thin, straight one. They point in slightly different directions.
To get an idea
Sunlight pushes the dust the way wind pushes smoke: gently, but always in the same direction.
Fun facts
These are not in the book: there was no room on paper.
Sunlight weighs nothing at all, and yet it manages to push the tiniest particles.
The solar wind blows from the Sun in every direction, and it never stops.
Sometimes perspective makes the two tails seem to point in opposite directions.
The Hubble telescope has searched for dead comet nuclei in the Kuiper Belt, without certain results.
A comet's tail is so thin that you could walk right through it without noticing.
The shape of the dust tail depends on where the Earth is compared with the comet.
Test yourself
The first question is the one printed under the QR code, with the answer the book did not give. The other four only exist here.
Question 1 of 5★ is the one from your book
Which way does a comet's tail point?
Question 2 of 5
How many tails does a comet usually have?
Question 3 of 5
Why is the dust tail yellowish?
Question 4 of 5
What is the solar wind?
Question 5 of 5
Where does the tail go when the comet moves away from the Sun?
Riddles
We are two sisters born together. I am wide, curved and golden; she is straight, thin and bluish. We point almost the same way, but not quite. What are we?
I am millions of miles long, but there is almost nothing inside me. I am born from a rock the size of a hill. What am I?
Try it yourself
Draw a comet moving away from the Sun and check that you put the tail in front: it is the most common mistake.
Look at a photo of a comet and try to tell the two tails apart: one wide and curved, the other straight and thin.
The words
- coma
- The cloud of gas and dust that surrounds the nucleus of a comet.
- ionized
- A gas whose particles have picked up an electric charge.
Sources: Wikidata (Q559875), Wikipedia (Coda (astronomia)).