According to a study, the sun’s radius might be slightly smaller than previously thought. The study defines the solar radius as 695,780 kilometers, which is only slightly smaller than the generally accepted radius of 696,000 kilometers. This is a difference of a few hundredths of a percent, or 100-200 kilometers.  

The study’s findings are based on sound waves generated and tapped inside the Sun’s hot plasma interior, known as “pressure” or p-modes. These p-waves are created by the movement of material inside the sun and can pass easily through its core. According to astrophysicists Masao Takata of the University of Tokyo and Douglas Gough of the University of Cambridge, p-mode oscillations offer a “dynamically more robust” view of the Sun’s interior. 

The study’s findings could have bigger implications on how we understand the workings of the sun’s internal structure.

The study defines the solar radius (half the diameter) as 695,780 kilometers… only slightly smaller than the generally accepted radius of 696,000 kilometers obtained by direct optical measurement. This is only smaller by a few hundredths of a percent, or 100-200 kilometers.

In astronomy, radius is the average distance from the center of an astronomical object to its surface. This is because planets and stars are not perfectly spherical. 

Here are some types of radii: 

• Planetary radius: The distance between a planet’s center and its surface. 
• Orbital radius: The distance between an object in orbit, such as a planet or a moon, and the center of the object it is orbiting. 

Some examples of radii include: 

• Earth radius: The distance from the center of Earth to a point on or near its surface. The Earth’s equatorial radius is 6,378 km and its polar radius is 6,357 km. 
• Solar system radius: 4.545 billion km. 
• Observable universe radius: 46.5 billion light-years. 

The most common units used to measure radius are the Earth radius, Jupiter radius, solar radius, and the kilometer (km)

The Sun’s radius is about 432,450 miles (696,000 kilometers). This makes its diameter about 864,938 miles (1.392 million km). The Sun’s radius is 109 times the Earth’s radius. 

The Sun is a medium-sized star. It’s more massive than Earth, with a mass that would take over 330,000 Earths to match. The Sun’s volume would take 1.3 million Earths to fill. 

The Sun’s surface gravity is 274 m/s2, which is 28 times that of Earth. Its mean density is 1410 kg/m3, which is 0.255 times the mean density of Earth. 

The Sun’s radius was measured by the SOHO spacecraft by timing Mercury’s transits across the Sun’s surface in 2003 and 2006. The result was a radius of 696,342 ± 65 kilometers (432,687 ± 40 miles).

The Sun is made of hot plasma, which is ionized matter. Plasma is one of the four fundamental states of matter. It’s characterized by a significant portion of charged particles, such as ions or electron

The Sun’s interior is a ball of swirling plasma that’s held together by gravity and pressure. The Sun’s core has a temperature of about 15.7 million kelvin (K) and a density of up to 150 g/cm3. The Sun’s surface temperature is about 5,800 K.

The Sun’s plasma rotates at different speeds on different parts of the Sun. At its equator, the Sun rotates once every 25 Earth days. At its poles, the Sun rotates once every 36 Earth days.

Sun is the most essential facet of modern astronomy: not only does Sol provide us with the only example of a star we can study up close, but the energy it provides fuels life on Earth, and the space weather it produces impacts our modern technological civilization

The study out of the University of Tokyo and the Institute of Astronomy at Cambridge was done looking at data from the joint NASA/ESA Solar Heliospheric Observatory (SOHO’s) Michelson Doppler Imager (MDI) imager. The method probes the solar interior via acoustics and a cutting edge field of solar physics known as helioseismology

Helioseismology is the study of the Sun’s interior and dynamics by observing the vibrations of its surface. The Sun is almost opaque to electromagnetic energy, so it takes about 170,000 years for radiation to reach the surface from the core.

Helioseismology uses three types of waves: Acoustic, Gravity, Surface gravity. 

These waves generate resonant modes of oscillation, called: p modes, g modes, f modes. 

Helioseismology has improved our understanding of the Sun’s interior. It has provided a detailed map of the Sun’s structure and internal rotation, and tested the physical inputs used to model stellar interiors. 

Helioseismology studies are divided into two groups: 

• Global helioseismology: Uses the Sun’s resonant modes 
• Local helioseismology: Uses all the waves propagating at the Sun’s surface 

The Helioseismic and Magnetic Imager aboard NASA’s Solar Dynamics Observatory is a primary source of data for helioseismologists.

Helioseismology is the study of seismic waves in the Sun’s interior. These sound waves can be used to probe the Sun’s interior, similar to how geologists use seismic waves from earthquakes to probe the Earth’s interior.  

Helioseismological studies have yielded many results about the Sun’s internal structure and dynamics. For example, helioseismology has shown that the Sun is slightly smaller than the generally accepted radius of 696,000 kilometers. This is only smaller by a few hundredths of a percent, or 100-200 kilometers. 

The Sun’s radius has been measured as 696,342 km (432,687 miles) with an uncertainty of only 65 km (40 miles). This was achieved by using the solar telescope aboard a NASA satellite.

Helioseismology has also confirmed or discovered the following about the Sun: 

• Rotation: The Sun’s deep interior rotates uniformly, like a solid object. This challenges the previous assumption that the Sun’s interior rotates differentially, with the equator spinning faster than the poles. 
• Convection: Convection extends inward from the surface 30% of the way toward the center. 
• Nuclear fusion: Nuclear fusion occurs only within the core of the Sun. 

Helioseismology can also help scientists: 

• Solve basic physics mysteries 
• Forecast space weather 
• Map the structure of sunspot groups below the surface 
• Detect sunspots on the far side of the Sun

The study of the Sun is called heliophysics. It involves studying the Sun and its influence on the solar system, Earth, space, and planets. Heliophysics research can help protect astronauts, spacecraft, and power grids

Other studies related to the Sun include: 

• Astronomy: The study of celestial objects, including the Sun, planets, stars, comets, galaxies, and more 
• Solar physics: A branch of astrophysics that specializes in detailed measurements of the Sun 
• Helioseismology: The study of the Sun’s interior by observing the vibrations of its surface

Previous studies relied on less accurate f-mode waves, which are surface waves considerably shorter than the solar radius. The study defines the solar radius (half the diameter) as 695,780 kilometers… only slightly smaller than the generally accepted radius of 696,000 kilometers obtained by direct optical measurement.(full article source google)

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