Eleanor Finch
The Sun's permanent position in the sky and the fact that the planets revolve around it may suggest that it is static and does not rotate. However, the rotation of the Sun was first discovered in the 17th century by Galileo, who observed the motion of dark spots on the Sun, now known as sunspots. Sunspots are the most widely used tracers for measuring the Sun's rotation, and the rotation rate at the equator is faster than at the poles. The Sun rotates on its axis once in about 27 days, and its rotation axis is tilted by about 7.25 degrees from the axis of the Earth's orbit. The Sun's rotation can also be observed through the spiral shape of its magnetic field, known as the Parker spiral, which is formed by the Sun's magnetic fields extending into space.
| Characteristics | Values |
|---|---|
| Sunspots | The movement of sunspots was first observed by Galileo in 1612, and they are still used today to measure the Sun's rotation. |
| Telescope observations | The use of telescopes allowed for the observation of sunspots turning with the Sun, providing evidence of solar rotation. |
| Tracers | The motion of "tracers", or features on the solar surface, is used to measure rotation constants. |
| Differential rotation | The Sun's rotation varies with latitude, with faster rotation at the equator and slower rotation at higher latitudes. |
| Synodic rotation period | The synodic rotation period is approximately 26.24 days, which is the time it takes for a fixed feature on the Sun to return to the same apparent position as viewed from Earth. |
| Sidereal rotation period | The sidereal rotation period is approximately 25.38 days, and it refers to the time it takes for the Sun to rotate when viewed from above Earth's North Pole. |
| Carrington rotation | The Carrington rotation is a system for tracking the Sun's rotation as seen from Earth, with a rotation period of approximately 27.2753 days. |
| Axis tilt | The Sun's rotation axis is tilted by about 7.25 degrees from the axis of the Earth's orbit. |
| Magnetic fields | The Sun generates magnetic fields that form the interplanetary magnetic field of our solar system. The Sun's rotation causes these magnetic fields to spin out into a large rotating spiral, known as the Parker spiral. |
| Composition | The Sun is composed of gaseous plasma, which allows it to rotate differently from solid planets and moons. |
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What You'll Learn
Sunspots
In 1612, Galileo wrote:
> "It is also manifest that their rotation is about the sun… to me, it seems more probable that the movement is of the solar globe than of its surroundings."
English scholar Thomas Harriot was probably the first to observe sunspots telescopically, as evidenced by a drawing in his notebook dated 8 December 1610. The first published observations (June 1611) were by Johannes Fabricius, who had been systematically observing the spots for a few months and had also noted their movement across the solar disc.
The Sun's rotation axis is tilted by about 7.25 degrees from the axis of the Earth's orbit, so we see more of the Sun's north pole in September and more of its south pole in March.
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Telescope observations
Galileo Galilei was another early astronomer to observe the Sun through a telescope. In 1612, he published his observations in "Sidereus Nuncius," where he noted the presence of spots on the Sun and their movement, indicating rotation. He understood that these spots were not planet-like objects because they changed shape and sometimes disappeared. Galileo projected the image of the Sun onto a screen to make careful drawings, as he knew that looking directly through the telescope could damage his eyes.
The use of telescopes allowed astronomers to track the movement of sunspots and other features on the Sun's surface, providing strong evidence of the Sun's rotation. This method of observing tracers on the solar surface has been widely used to measure the rotation constants. The rotation rate at different latitudes has been found to vary, with the equatorial regions rotating faster (approximately 24 to 25 days) than the polar regions (approximately 30 to 33 days).
In addition to telescope observations of sunspots, modern astronomers have employed other techniques to study the Sun's rotation. They have utilized spectroheliographs to detect intense magnetic fields within the dark regions of sunspots, further confirming their relationship with the Sun's rotation. NASA's Solar and Heliospheric Observatory (SOHO) has estimated that the core of the Sun rotates once a week, four times faster than its surface. This differential rotation is attributed to the conservation of angular momentum from the gas cloud that formed the Sun approximately 4.5 billion years ago.
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The sun's magnetic field
The Sun's rotation was first discovered in the 17th century by Galileo, who observed the motion of sunspots—dark patches on the Sun's surface—through a telescope. Since then, astronomers and solar scientists have continued to use these tracers to measure the Sun's rotation.
The Sun rotates on its axis once in about 27 days, but this varies with latitude. The Sun's equatorial regions rotate faster, taking about 24-25 days, while the polar regions take more than 30 days to complete a rotation. This is known as differential rotation, and it is because the Sun is composed of gaseous plasma, not solid matter.
Additionally, the Sun's rotation can be observed through the retrograde motion of other planets in our solar system, such as Mars and Mercury. By studying the movements of these planets, we can gather evidence of the Sun's influence and its role in shaping the orbits of nearby celestial bodies.
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The sun's equatorial rotation rate
The Sun rotates on its axis as it revolves around the galaxy, with a spin tilt of about 7.25 degrees concerning the planets' orbits plane. The Sun's rotation axis is tilted by about 7.25 degrees from the axis of the Earth's orbit. Due to its gaseous plasma composition, the Sun does not rotate uniformly like solid planets and moons. Instead, it experiences differential rotation, with varying rotation rates across its surface.
The Sun's equatorial regions rotate faster, taking approximately 24 to 25 days, while the polar regions have a slower rotation rate, completing a full rotation in over 30 to 36 days. This variation in rotation rates at different latitudes was first measured by Christoph Scheiner in 1630, who is considered the discoverer of solar differential rotation. The rotation constants are determined by observing the motion of features on the solar surface, such as sunspots, which are dark cool patches resulting from the Sun's rotation.
The Sun's rotation can be observed through its impact on its magnetic fields. The Sun generates magnetic fields that extend into space, forming the interplanetary magnetic field of our solar system. As the Sun rotates, this magnetic field takes on a rotating spiral shape, known as the Parker spiral. Additionally, the Sun undergoes phases of high and low activity, resulting in an approximately 11-year cycle where its geographic poles change magnetic polarity.
The Sun's rotation is also evident when observing the motion of planets and celestial bodies in our solar system. The retrograde motion observed in planets like Mars and Mercury can be more simply explained by their orbits around the Sun rather than the Earth. Furthermore, the Sun's rotation contributes to the variation in sunlight distribution across the globe, influencing the concept of time zones.
In summary, the Sun's equatorial rotation rate is faster than that of its polar regions, and this variation in rotation rates constitutes evidence of the Sun's differential rotation. This discovery was made through observations of sunspots and is further supported by the Sun's impact on its magnetic fields and the motion of celestial bodies in our solar system.
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The Carrington rotation
The Sun rotates on its axis once in about 27 days. This rotation was first detected by observing the motion of sunspots. The Sun's rotation axis is tilted by about 7.25 degrees from the axis of the Earth's orbit. As the Sun is composed of gaseous plasma, its rotation is more complex than that of solid planets and moons. The Sun experiences differential rotation, meaning that its rotation rate varies depending on the latitude observed. The rate of surface rotation is the fastest at the equator and decreases as latitude increases.
Sunspots have been used since ancient times to measure the rotation constants of the Sun. The English scholar Thomas Harriot was likely the first to observe sunspots telescopically, with the first published observations by Johannes Fabricius in June 1611. Christoph Scheiner, in 1630, was the first to measure the equatorial rotation rate of the Sun and notice that the rotation at higher latitudes is slower.
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Frequently asked questions
The Sun rotates on its axis once in about 27 days. However, its rotation period varies with latitude, ranging from 24 days in the equatorial regions to over 30 days in the polar regions.
The Sun's rotation was first discovered in the 17th century by Galileo, who observed the motion of sunspots through a telescope.
Today, scientists use various methods and technologies to study the Sun's rotation, including telescopes, spacecraft, and the analysis of its magnetic fields and solar wind.
