# Third Kepler's Law

Enter 'x' in the field to be calculated.

## Introduction to Kepler's Law

Kepler's Law is a cornerstone in astronomy, describing the movements of planets in our solar system and beyond. It establishes a relationship between the orbital period of a celestial body and its semi-major axis, linked by the gravitational pull of the star around which it orbits. This law allows astronomers to calculate crucial information about the orbits of celestial bodies.

## Explanation of the Formula

The formula of Kepler's Law is expressed as follows: `T^2 = (4*pi^2)/(G*M)*a^3`.

Each variable represents a key aspect of the orbit:

**T**: Orbital period, the time it takes an object to complete an orbit around the star.**a**: Semi-major axis of the orbit, a measure of the size of the orbit.**G**: Gravitational constant, a universal constant quantifying the force of gravity.**M**: Mass of the star, around which the object orbits.

## How to use our Calculator?

To use our Kepler's Law calculator, follow these simple steps:

**Entering Data and Units:**Enter the values of the three known variables in the corresponding fields. Make sure to use the correct units. For example, for the average distance between the Earth and the Sun, use "1 AU" (astronomical unit), equivalent to the Earth-Sun distance.**Choosing the Variable to Calculate:**Leave empty or enter 'x' in the field of the variable you wish to calculate. The calculator will determine this value based on the other three values provided.**Converting Results:**After obtaining the result, you can use the link provided next to the result to convert this value into different units. This is particularly useful for comparing or using these results in other contexts or calculations.

Our calculator is designed to be intuitive and easy to use, while providing accurate results in accordance with Kepler's Law.

## Practical Applications

Kepler's Law has numerous applications in astronomy and astrophysics. It allows determining the characteristics of the orbits of planets, natural and artificial satellites, and even exoplanets. For example, it helps calculate a planet's distance from its star, which is crucial for understanding its climate and the possibility of harboring life.

## Calculated Examples

### Example with the Earth and the Sun

Consider the Earth orbiting the Sun. The orbital period (T) of the Earth is about 365.25 days, and the average distance (semi-major axis a) of the Earth to the Sun is about 149.6 million kilometers. The mass (M) of the Sun is about 1.989 × 10^{30} kg. Using the formula `T^2 = (4*pi^2)/(G*M)*a^3`, we can verify these values or calculate one of them if the other three are known.

### Example with the International Space Station (ISS)

Consider the International Space Station (ISS) orbiting Earth. The orbital period (T) of the ISS is about 90 minutes (1.5 hours), and it orbits at an average altitude of about 400 km above the Earth's surface. With the Earth's radius of about 6371 km, this gives a semi-major axis (a) of about 6771 km (6371 km + 400 km). The mass (M) of the Earth is about 5.972 × 10^{24} kg. Using the formula `T^2 = (4*pi^2)/(G*M)*a^3`, we can calculate and verify the orbital period or semi-major axis of the ISS's orbit, based on the other known values.

## FAQ

- Q1: Does Kepler's Law apply to artificial satellites?
- A: Yes, Kepler's Law can be used to calculate the orbits of artificial satellites around the Earth or other bodies.
- Q2: How is the gravitational constant G determined?
- A: The constant G was measured by scientific experiments, the most famous being the Cavendish experiment in the 18th century.
- Q3: Is this law valid for all celestial bodies?
- A: The law is generally valid for bodies orbiting around a much larger mass, but exceptions exist, especially in extreme situations like near black holes.
- Q4: Can this law be used to predict the future positions of planets?
- A: Yes, by knowing the orbital parameters, it is possible to predict the future positions of celestial bodies with great accuracy.

## See also

Movement Calculators

Unit Converter