The numbers
- Temperature of a spot
- 6,739°F(3,726 °C)
- Temperature all around
- 6,000K
- How often they come back in numbers
- 11years
How it happens, step by step
The field tangles
The Sun does not spin all at the same speed, and this twists the lines of its magnetic field until they tangle.
The bundle rises
A group of tangled lines rises and crosses the surface, going in at one point and coming out a little farther on.
The heat slows
Where the field is strong, the churning that brings heat up from below slows down. Less energy reaches that area.
A spot appears
The area cools by about 3,600 degrees Fahrenheit. It is still very bright, but next to its surroundings it looks dark.
The cycle restarts
After days or weeks the spot closes up. The number of spots rises and falls over a cycle of about eleven years.
To get an idea
A spot and what surrounds it differ by about thirty-six hundred degrees Fahrenheit.
It is like a lit bulb seen in front of a lighthouse: it is on, but you cannot see it.
Fun facts
These are not in the book: there was no room on paper.
For much of the 1600s the spots almost disappeared: that period is called the Maunder Minimum.
The eleven-year cycle was discovered by Heinrich Schwabe, who published the result in 1843.
In 2008 the Sun had no spots at all on two hundred sixty-six days out of three hundred sixty-six.
Other stars have spots too, and in that case they are called starspots.
On the first of September 1859, a flare knocked out the telegraphs and brought auroras very close to the equator.
Sunspots have been counted since 1700 and estimated back as far as 1500.
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
Why does a sunspot look dark?
Question 2 of 5
What cools that area?
Question 3 of 5
How often do sunspots come back in large numbers?
Question 4 of 5
What did sunspots prove in the 1600s?
Question 5 of 5
How do you observe them safely?
Riddles
People looked at me through a telescope in the 1600s and I made the philosophers angry, because I proved that something believed perfect spins and changes. What am I?
I come back in large numbers about every eleven years, and I am born where the invisible threads of magnetism tangle and poke through the surface. What am I?
Try it yourself
Turn on a flashlight and look at it during the day in front of a bright window: it seems to be off. It is the same contrast that makes sunspots dark.
Look online for today's picture of the Sun and count the spots. Do it again a month later: the number changes, and the groups have moved.
The words
- magnetic field
- The invisible force that pulls or pushes, like the force of magnets.
- flare
- A sudden flash of energy released near a group of spots.
Sources: Wikidata (Q40015), Wikipedia (Macchia solare).