Solve Hubble's Law: Proxima Centauri & Sun in Milky Way

• Fabio010
In summary, the problem involves determining the recessional velocity of the nearest star, Proxima Centauri, as the space between it and the sun is expanding according to Hubble's law. By using the equation H_0 = v/D and the estimated distance of the star from the sun, a recessional velocity of 0.33 km/h is calculated. However, this value is significantly smaller than the speed of the sun in our galaxy (estimated to be between 210-240 km/s), indicating that there may be an error in the calculation.
Fabio010

Homework Statement

Determine for the nearest star what should be it's recessional velocity if the space between the two stars is expanding according to the Hubble's law. Compare this value with the speed of the sun when it moves with Milk Way.

Homework Equations

$H_{0} = \frac {v}{D}$

$H_{0}\approx 72 km/s/Mpc$Nearest Star: Proxima Centauri

distance from sun : 4.2421ly = $1,30 pc$

The speed of the sun in Milk Way is approx. $828km/h$

The Attempt at a Solution

$v = \frac{72km}{s} * \frac {1,30 pc }{1Mpc}$

$v = 9,11 * 10^{-5}km/s = 0,33 Km/h$

if we compare with the speed of the sun in milk way, we can see that the recessional velocity between the two stars is much smaller.

my friend said that the problem is not well solved. But i do not remember his explanation.

Can u tell me if it is wrong? If yes where is the error?

Your conclusion is correct, but you underestimated the speed of the sun in our galaxy significantly.

mfb said:
Your conclusion is correct, but you underestimated the speed of the sun in our galaxy significantly.

"Away from the central bulge or outer rim, the typical stellar orbital speed is between 210 and 240 km/s"

Instead of $828km/h$ it is $828000km/h$

Thanks for the help!

Last edited:

1. What is Hubble's Law?

Hubble's Law is a fundamental principle in astronomy that describes the relationship between the distance of a galaxy or celestial object and its velocity. It states that the further away an object is, the faster it is moving away from us.

2. How does Hubble's Law relate to Proxima Centauri and the Sun in the Milky Way?

Hubble's Law can be used to calculate the distance and velocity of objects within our own galaxy, such as Proxima Centauri (the closest star to our Sun) and the Sun itself. By measuring the redshift of their light, we can determine their velocities and use Hubble's Law to calculate their distances.

3. What is the significance of Proxima Centauri and the Sun in Hubble's Law?

Proxima Centauri and the Sun are important examples in Hubble's Law because their relatively close distance to each other and to Earth allows for more accurate measurements of their velocities and distances. This data can then be used to refine and improve our understanding of Hubble's Law and the expansion of the universe.

4. Can Hubble's Law be used to study objects outside of the Milky Way?

Yes, Hubble's Law can be applied to objects outside of our own galaxy. It has been used to study the expansion of the entire universe and to measure the distances of distant galaxies. However, the accuracy of these measurements may be limited due to the large distances and uncertainties in their velocities.

5. How does Hubble's Law contribute to our understanding of the universe?

Hubble's Law is a key piece of evidence for the theory of the expanding universe. It shows that galaxies and celestial objects are moving away from us at increasing speeds, providing support for the concept of the Big Bang and the continuous expansion of the universe.

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