# Orbital Radius of a Jovian Moon

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• Forcino
In summary, the first scientists were able to figure out the orbital radius of a moon of Jupiter by using the equation D = θ d / 206,265 where D is the linear size of the object, θ is the angular size of the object in arcseconds, and d is the distance to the object. This distance can be determined by using a telescope to view Jupiter and measuring the angular distance of the moon over several orbits. However, it doesn't have to be at opposition and multiple measurements are needed for a more accurate estimate. In the 17th century, Römer used this method to determine the distance to Jupiter, with a small margin of error due to inaccuracies in measuring the speed of light. His distance was
Forcino
TL;DR Summary
How did the first scientists figure out the orbital radius of a moon of Jupiter? How can observations lead to a calculation of the orbital radius of a moon of another planet?
How did the first scientists figure out the orbital radius of a moon of Jupiter? How can observations lead to a calculation of the orbital radius of a moon of another planet?

Thank you.

So would you find the orbital radius of a Jovian moon by using a telescope to view Jupiter at opposition during a time when the moon is farthest from Jupiter? Then you could find the arcseconds of angle from the center of Jupiter to the center of the moon? Then you could use the equation D = θ d / 206,265? Then D would be the orbital radius of the moon?

Yeah, although:
1. it doesn't really have to be at opposition
2. you'd need to measure the angular distance of the moon over several/many orbits to get a good estimate of the maximum orbital radius.

Drakkith
How did the scientists figure out distance to Jupiter back in 17th century? Römer measured speed of light by 1676, but he got the speed about 30% too slow. How much of it was the error in travel time, how much the error in distance to Jupiter?
How much was Römer´s distance in 1676 better than Galilei´s distance, if any, in 1610?

## 1. What is the orbital radius of a Jovian moon?

The orbital radius of a Jovian moon refers to the distance between the center of the moon and the center of the planet it orbits. It is typically measured in kilometers or astronomical units (AU).

## 2. How is the orbital radius of a Jovian moon determined?

The orbital radius of a Jovian moon is determined by measuring its average distance from the planet over a full orbit. This can be done using telescopes, spacecraft, or mathematical calculations based on the moon's orbital period and speed.

## 3. What is the average orbital radius of Jovian moons?

The average orbital radius of Jovian moons varies depending on the specific moon and its distance from the planet. For example, some of Jupiter's moons have an average orbital radius of around 1 million kilometers, while others have an average of over 20 million kilometers.

## 4. How does the orbital radius of a Jovian moon affect its orbit?

The orbital radius of a Jovian moon plays a significant role in determining the moon's orbital period and speed. A larger orbital radius will result in a longer orbital period and slower speed, while a smaller orbital radius will result in a shorter orbital period and faster speed.

## 5. How does the orbital radius of a Jovian moon change over time?

The orbital radius of a Jovian moon can change over time due to various factors, such as gravitational interactions with other moons or external forces. However, these changes are typically very small and may only be noticeable over long periods of time.

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