The rotation period is about 25 days at the equator, 28 days at latitude 40°, and 36 days at latitude 80°. Modern observations show that the speed of rotation of the Sun varies according to latitude, that is, it’s different as you go north or south of the Sun’s equator. The Sun, however, is a gas and does not have to rotate rigidly, the way a solid body like Earth does. Our star turns in a west-to-east direction, like the orbital motions of the planets. Galileo, in 1612, demonstrated that the Sun rotates on its axis with a rotation period of approximately 1 month. (credit: modification of work by SOHO/NASA/ESA)īy recording the apparent motions of the sunspots as the turning Sun carried them across its disk (Figure 2). This region produced many flares and coronal mass ejections. On March 30, 2001, this group of sunspots extended across an area about 13 times the diameter of Earth. Sunspots Rotate Across Sun’s Surface: This sequence of photographs of the Sun’s surface tracks the movement of sunspots across the visible hemisphere of the Sun. Like storms on Earth, sunspots are not fixed in position, but they drift slowly compared with the Sun’s rotation.įigure 2. The largest groups are very complex and may have over 100 spots. Frequently, spots occur in groups of 2 to 20 or more.
Many spots become much larger than Earth, and a few, like the largest one shown in Figure 1 have reached diameters over 140,000 kilometers. If a spot lasts and develops, it usually consists of two parts: an inner darker core, the umbra, and a surrounding less dark region, the penumbra. Individual sunspots come and go, with lifetimes that range from a few hours to a few months. They appear dark only in contrast with the hotter, brighter photosphere around them. If they could be removed from the Sun, they would shine brightly. While we understand that sunspots look darker because they are cooler, they are nevertheless hotter than the surfaces of many stars. This is the one area of astronomy where we don’t encourage you to do your own observing without getting careful instructions or filters from your instructor.) (We emphasize what your parents have surely told you: looking at the Sun for even a brief time can cause permanent eye damage. Occasionally, these spots are large enough to be visible to the unaided eye, and we have records going back over a thousand years from observers who noticed them when haze or mist reduced the Sun’s intensity. They look darker because the spots are typically at a temperature of about 3800 K, whereas the bright regions that surround them are at about 5800 K (Figure 1). The first evidence that the Sun changes came from studies of sunspots, which are large, dark features seen on the surface of the Sun caused by increased magnetic activity. (credit: NASA Goddard Space Flight Center, Alan Friedman) The mottled appearance of the Sun’s surface is granulation.
#Are sunspots hotter than the photosphere full
Although sunspots appear dark when seen next to the hotter gases of the photosphere, an average sunspot, cut out of the solar surface and left standing in the night sky, would be about as bright as the full moon. The largest spot shown here is about 11 Earths wide. You can see the dark, central region of each sunspot (called the umbra) surrounded by a less dark region (the penumbra).
Sunspots: This image of sunspots, cooler and thus darker regions on the Sun, was taken in July 2012.
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