How a 001 sunspot moved with the spinning Sun snapped from space

TRACKING SUNSPOTS
How a 2001 sunspot moved with the spinning Sun
1 SNAPPED FROM SPACE
This series of images was taken by the Solar and Heliospheric Observatory in March 2001. It was called active region 9393 and spanned 150,000 miles across the Sun’s surface.
2 SHOWING MOVEMENT
Over the course of a week the sunspot appeared to have travelled thousands of miles, from one side of the Sun to the other.
A DIFFERENTIAL ROTATION
Because the Sun isn’t solid, different regions rotate at different rates. A single rotation at the Sun’s equator takes 25 days, but takes 28 days at latitude 40 degrees and 36 days at latitude 80 degrees.
B SOLAR SPEEDS
At the equator, the Sun spins around 41,000 miles per day.
C BIGGER THAN EARTH
Active region 9393 was more than 13 times the size of Earth’s surface.
SPOTTING SUNSPOTS
Taking inspiration from the work of German astronomer Christoph Scheiner, Galileo also pointed his telescope at the giant ball of light in the sky in search of sunspots. We now understand that sunspots are the sites of solar flares and coronal mass ejections, forming dark spots on the Sun’s surface that burn at thousands of degrees. They form as a result of the Sun’s twisting magnetic fields, which produce sudden bursts of solar activity. Galileo was none the wiser about the source of these solar anomalies, but he did use them to discover that the Sun was moving. Scheiner concluded sunspots weren’t fixed to the surface of the Sun, but were instead small planets closely orbiting it. Galileo contested this, instead suggesting that the markings confirmed that the Sun is rotating on an axis. While observing the Sun and its spots, Galileo noticed that the dark spots moved, vanished and returned over time.

A sunspot, almost 80,000 miles wide, captured by NASA’s Solar Dynamics Observatory in 2014

THE PHASES OF VENUS
Three years after his groundbreaking observations, Galileo published his Letter on Sunspots in 1613. In this, Galileo offered a more disruptive finding about Earth’s neighbour Venus. Before Galileo’s telescope, the sunlight reflected from the surface of Venus led people to believe it was nothing more than another star. To the naked eye, Venus appears to rise ahead of the Sun at dawn and behind it at dusk. In the Ptolemaic model of the Solar System, this was attributed to Venus moving in a circle as well as orbiting Earth. In the morning, Venus would be at the front most point in its mini orbit, then at the farthest most point during the evening, making it look like it was behind the Sun.
But when Galileo took a look at Venus, he discovered that it didn’t appear as it should according to the Ptolemaic model. For the Ptolemaic model to be correct, we wouldn’t be able to see the fully sunlit side of Venus, only the light at the edges at the extremes of its mini orbit. However, this isn’t what Galileo saw. Over several months, Galileo tracked the so-called star and discovered that, like the Moon, Venus entered a series of phases. The only way that Galileo could witness the stages of change from a full, brightly lit Venus to an unlit ‘new’ planet is if Venus orbited the Sun rather than Earth. Galileo’s discovery of Venus’ phases meant that Copernicus’ model of a heliocentric system was justified.


One of Galileo’s many planetary drawings depicting the phases of Venus, as well as Saturn, Mars and Jupiter