# Radial Velocity of the Sun around Galactic Centre

• anyaxo
In summary, the conversation discusses the attempt to calculate the radial velocity of the sun using Newton's Laws of Gravitation. However, the calculated value is significantly lower than the actual value of 220000 m/s. It is discovered that the mass used in the equation should be the mass of the galaxy, not just the sun.
anyaxo
I need to calculate the radial velocity of the sun. Every time I try using Newton's Laws of Gravitation, I end up getting a value of 0.733 m/s. Apparently the actual value is 220000 m/s.

Mass of Sun = 1.99 x 10^30 kg (3sf)
G = 6.67 x 10^-11 Nm^2kg^-2
r = distance of Sun from galactic centre = 8.0 kpc = 2.47 x 10^20 m

mv^2/r = -GMm/r^2
v^2 = GM/r

v^2 = (6.67 x 10^-11 (1.99 x 10^30))/(2.47 x 10^20)
= 0.537...
v = 0.733 m/s (3sf)

What am I doing wrong?! This is driving me insane.

since sun is rotating around the center of the galaxy, m would be the mass of the sun.
it gets canceled here. so M is actually mass of the galaxy and not the sun.

## 1. What is the radial velocity of the Sun around the Galactic Centre?

The radial velocity of the Sun around the Galactic Centre refers to the speed at which the Sun is moving in a circular orbit around the centre of the Milky Way galaxy. This velocity is approximately 220 km/s.

## 2. How is the radial velocity of the Sun around the Galactic Centre measured?

The radial velocity of the Sun is measured using the Doppler effect, which is the change in frequency of light as an object moves towards or away from an observer. Scientists use this effect to measure the small shifts in the wavelength of light coming from stars in the Milky Way, allowing them to determine the radial velocity of the Sun.

## 3. What factors affect the radial velocity of the Sun around the Galactic Centre?

The radial velocity of the Sun is affected by several factors, including the gravitational pull of the other objects in the Milky Way, such as stars, planets, and dark matter. Additionally, the distribution of matter in the galaxy and the overall shape of the galaxy can also influence the radial velocity of the Sun.

## 4. How does the radial velocity of the Sun affect the overall movement of the Milky Way?

The radial velocity of the Sun is just one component of the overall movement of the Milky Way. The Sun's orbit, along with the orbits of billions of other stars, contributes to the overall rotation and movement of the galaxy. Understanding the radial velocity of the Sun helps scientists to better understand the dynamics of the Milky Way and its place in the universe.

## 5. Has the radial velocity of the Sun around the Galactic Centre changed over time?

Yes, the radial velocity of the Sun has changed over time. Scientists have observed that the Sun's velocity has increased in the past and may continue to change in the future. These changes are due to various factors, such as the gravitational influence of other objects in the galaxy and the evolution of the Milky Way itself.

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