Why do sunspots move across the sun

In recent years, astronomers have been able to detect "starspots" - "sunspots" on other stars. Skip to main content. More about Sunspots. More about the Sun. The surface of the Sun is a very busy place. It has electrically charged gases that generate areas of powerful magnetic forces. These areas are called magnetic fields. This motion creates a lot of activity on the Sun's surface, called solar activity.

Other times, things are a bit quieter. The amount of solar activity changes with the stages in the solar cycle. Solar activity can have effects here on Earth, so scientists closely monitor solar activity every day. Sunspots are areas that appear dark on the surface of the Sun. By: Patrick J. Sunspots appear dark to us because they're cooler than the surrounding areas on the sun's visible surface, or photosphere , which has a temperature of about 10, degrees Fahrenheit 5, The dark interior of a sunspot, called the umbra , is about 1, degrees cooler than the rest of the sun's surface.

That interior is surrounded by a larger, lighter area called the penumbra , which is about degrees cooler than the rest of the sun.

Sunspots are cooler because they're areas of intense magnetism -- so intense that it inhibits the flow of hot gases from the sun's interior to its surface. Sunspots occur because the sun isn't a hunk of rock like the Earth and the inner planets, but a ball of continually circulating hot gases that doesn't move in one piece. The interior and the exterior of the sun rotate separately; the outside rotates more quickly at the equator than at the solar north and south poles.

Specifically, a point on the equator takes 25 Earth days to go around, while a point near one of the poles takes 36 days to complete its rotation. The intense magnetic fields are responsible for this cooling. Since magnetic fields produce pressure, plasma inside sunspots is forced out to maintain pressure equilibrium between the sunspot gas pressure plus magnetic pressure and the surrounding plasma gas pressure.

Therefore the plasma inside the sunspot is less dense and a little cooler if we compare the inside and outside of a sunspot at the same geometrical depth. Sunspots usually clump together in groups and have lifetimes between several days and weeks. Sunspots are dynamic and evolve together with the magnetic field: they appear, change, disappear. The dataset proposed in this activity is chosen close to the solar maximum, in order to display a large number of sunspots.

Sunspots are found in patches like storms on Earth, and are usually located in bands in both the northern and southern hemispheres. The bands that sunspots form in, move from mid latitudes to almost the equator throughout the year sunspot cycle.

Note that individual sunspots do not drift much in latitude since they only exist for a few weeks - just the latitudes where new spots form move towards the equator. Visit Solar Center website for more information on solar magnetograms. Visit Solar Dynamics Observatory website for more information on visible light images of the Sun.

Like the Earth, the Sun has a north pole and a south pole, and rotates around its axis. As seen from the Earth the Sun rotates about its axis once every about 27 days. Seen from above the solar north pole, the Sun rotates counter-clockwise. Rigid objects do not change shape i. Therefore, when rigid objects spin every part rotates at the same rhythm.

This means that every part of the object takes the same amount of time to complete a turn. This is called rigid rotation. This is the reason why every spot on Earth takes 24 hours to complete a turn. In non-rigid objects, i. This is the case of the Sun, since it is made up of a gaseous matter called plasma. Like the Earth, the Sun has a North pole and a South pole, and rotates around its axis.

This means that plasma can rotate at different speeds, depending on the latitude they are at: i. This is called differential rotation. As seen from space, the atmosphere rotates in less than 24 hours at mid latitudes and in more than 24 hours near the equator. Differential rotation is not a unique aspect of the Sun; it is common for rotating bodies such as other stars and gaseous planets to have different rotation rates at different latitudes.

Visit Swinburn University Cosmos website for more information. It was launched into an orbit around the Earth in and it has been observing the Sun since then. Visit Solar Dynamics Observatory website for more information. Galileo Galilei was one of the first astronomers to point a telescope to the Sun, in preceded by Thomas Harriott and Johannes Fabricius.

To his great surprise, he observed spots on the Sun, and made the drawings shown in Fig. He was very confused by the nature of these spots…. A hypothesis is a guessed explanation of a phenomenon. In our case, the phenomenon is the sunspots and their apparent displacement across the Sun. Ask the students to come up with several hypotheses about the sunspots and the causes of their apparent motion. Guide them to the following ones:.