# Radius of planet from Transits

• Jhero
In summary, the radius of a planet can be determined by knowing the maximum depth in brightness of a transiting planet over a star, as long as the size and brightness of the star are known. The distance between the planet and star does not affect the reduction in brightness, and the dip in brightness can be calculated using the formula (Rp/Rs)^2, where Rp is the planet radius and Rs is the star's radius. The absolute brightness of the star is not necessary, but knowing its radius is important.
Jhero
Hi, is there a way to find the radius of a planet by only knowing that the maximum depth in brightness of a transiting planet over a star is 0.7% ?

Assuming you are talking about exoplanets, you could, if you know the size and brightness of the star (which you probably do). As the distance from Earth to the star is much larger than from the planet to the star, the distance between the planet and star does not affect the reduction in brightness.

This is basically just working out the fractional projected area of the planet relative to the star. So the dip in brightness should be something like (Rp/Rs)^2 where Rp is the planet radius and Rs is the star's radius. The absolute britghness of the star is not necessary if you know the dip is 0.7% but you will need to know it's radius and this will probably come from brightness measurements anyway!

## 1. What is the radius of a planet from transits?

The radius of a planet from transits is the distance from the center of the planet to its outermost point. This measurement is typically given in kilometers or miles.

## 2. How is the radius of a planet from transits measured?

The radius of a planet from transits is measured by observing the planet as it passes in front of its star, causing a dip in the star's brightness. By analyzing the depth and duration of the dip, scientists can calculate the size of the planet and thus its radius.

## 3. Why is the radius of a planet from transits important in exoplanet research?

The radius of a planet from transits is an important factor in determining the composition and structure of exoplanets. By combining the radius measurement with other data, such as mass and temperature, scientists can gain a better understanding of the planet's atmosphere, surface conditions, and potential for hosting life.

## 4. Can the radius of a planet from transits change over time?

Yes, the radius of a planet from transits can change over time due to various factors such as atmospheric changes, tidal forces, and volcanic activity. However, these changes are typically small and can only be detected with advanced observation techniques.

## 5. How does the radius of a planet from transits compare to the size of Earth?

The radius of a planet from transits can vary greatly, with some exoplanets being much larger or smaller than Earth. However, it is a useful measurement for comparing the size and composition of planets in our universe and understanding the diversity of planetary systems.

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