How long does it take the sun to rotate?
Many objects in space rotate. Earth completes one rotation in about 24 hours, while Venus makes one enormous revolution 243 earth days. THE the rotation period of the moon is approximately 27 days. It turns out that the sun also rotates. So how long does it take for the Sun to rotate?
The answer depends on your vantage point in space and which part of the sun you measure.
In 1612, Galileo Galilei looked at the sun through a telescope, drew what he saw, and observed that sunspots – dark areas near the sun’s surface – moved across the solar surface over time. “Galileo followed a bunch of [sunspots] and I came to the conclusion that the sun was rotating”, J.Todd Hoeksemasolar physicist at Stanford University, told Live Science. By determining how fast sunspots moved around the sun, Galileo discovered that the sun rotated once every 28 days. But that number doesn’t tell the whole story of how fast the sun rotates.
Centuries later, in the mid-1800s, English astronomer Richard Carrington also measured the rotation speed of the sun using essentially the same methods as Galileo, but with a better telescope, Hoeksema explained. Carrington determined the speed at which sunspots rotated in a particular region – about 30 degrees latitude (on the sun) – where sunspots were most often observed. According to Carrington’s measurements, the sunspots were moving at a speed that would take them about 27.3 days to circle the sun.
Most sunspots come and go within a week or two, so they don’t last a full rotation, Hoeksema said. Despite this, astronomers like Galileo and Carrington were able to map the movement of sunspots over the course of days to determine how fast the sun rotated and, from there, how long it would take to complete a full rotation, Hoeksema explained.
However, the rotation of the Earth disrupts these calculations. Since the Earth moves around the sun and the sun rotates in the same direction, a measurement of solar rotation taken from Earth captures how fast the sun rotates relative to the sun. movement of the Earth. This type of measurement is called a synodic rotation rate and is almost two days longer than a measurement relating to the movement of stars (called a sidereal rotation rate), said Nicolas Viallresearch astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Carrington’s rate of 27.3 days includes those two extra days, Viall said.
So the sun actually makes more than one complete rotation during the 27.3-day Carrington rotation period, Viall said. Despite this, Carrington’s turnover rate was “eventually adopted as the standard by everyone,” Hoeksema said.
However, scientists now know that compared to the motion of stars, which is so slow as to be negligible in this context, Viall said, the sun would take about 25.4 days to rotate on its axis at the solar latitude where Carrington was observing sunspots.
“From a purely physical point of view, the sidereal rate is the correct rotation rate,” Viall said. For this reason, this article will now use sidereal rotation rates.
Latitude and depth
Researchers like Carrington have had to rely on visible features of the sun, like sunspots, to determine how fast the sun rotates. The problem is that not all regions of the sun have sunspots, Hoeksema said. There are “essentially no sunspots” at the poles and “relatively few” at the equator, he noted, so researchers who rely on sunspots to measure the sun’s rotation speed are limited by where on the sun they can take the measurement.
Taking measurements at different locations on the sun is necessary to get a complete picture, because the sun’s rotation speed depends on latitude (of the sun) and depth, according to Hoeksema.
“Interestingly, there is no single rotation rate that describes the sun,” he said. “Each side seems to have its own price.” This phenomenon, called differential rotation, is possible on the sun because it is made of gas. Earthon the other hand, does not rotate differentially because it is solid; all its parts must move together.
Starting in the 1970s, scientists began observing solar rotation using methods other than visual observation. One of them is helioseismology, “which uses sound waves that travel inside the sun to determine its characteristics,” Hoeksema explained.
Scientists can also measure the rotation of the sun by observing Doppler shifts, where light waves become shorter or longer as they move closer or further away from you, in the light emitted by the rotating sun.
By combining these data sources, scientists learned that the Sun rotates fastest at its equator, where it completes one rotation in 24.5 days, and slowest at its poles, where one rotation takes 34 days or more. This latitude-based variation occurs from the sun’s surface to the bottom of the convection zone, a layer of the sun that extends about a third of the way to the core.
In this same region, the sun’s rotation speed also varies with depth, Hoeksema explained. Even deeper in the sun, the radiative zone – which lies between the convection zone and the sun’s core – rotates like a solid, at a rate of about 26.6 days, regardless of latitude.
Scientists don’t know exactly how fast the sun’s core rotates, Hoeksema said, because researchers don’t have good measurements there.
This is “something people will have to understand in the future,” Hoeksema said.
Soleil Quiz: How well do you know our local star?
