How many times brighter will a star be then an identical star that's twice as far away?

Answer 1

Light intensity is one of those things ... along with gravitational force, electrostatic force,

and radio-station strength ... that follows the "inverse square" law, meaning that it decreases

in proportion to the square of the distance.

So if the distance is doubled, then the light intensity is 1/(2)2 = 1/4 its original value.

Answer 2

As it moves away from its source, light spreads out. The amount of 'spread' depends on how far the light has gone, and this is where the difference in brightness comes from.

The amount of light received at a given distance can be calculated by the inverse square law: the amount of light from a total L at a distance d is equal to L/d2. Thus, at twice the distance, it has only one quarter the light, or equivalently a star half as far away will be four times brighter.

Answer 3

4 times brighter, assuming extinction is negligible (i.e., not much light is lost through interstellar dust and gas). This is an inverse-square law.

4 times brighter, assuming extinction is negligible (i.e., not much light is lost through interstellar dust and gas). This is an inverse-square law.

4 times brighter, assuming extinction is negligible (i.e., not much light is lost through interstellar dust and gas). This is an inverse-square law.

4 times brighter, assuming extinction is negligible (i.e., not much light is lost through interstellar dust and gas). This is an inverse-square law.

Answer 4

Excluding the Sun, the brightest star as seen from Earth is Sirius, which is about twice as far away as the nearest (known) star, Proxima Centauri.

The second brightest star is Canopus. Sirius isn't intrinsically especially bright, if it weren't so close, it wouldn't be particularly noticeable. Canopus, on the other hand, is intrinsically extremely bright, but it's also over 30 times further away. Canopus is (probably) the brightest star within 700 light years or so.

Rigel, 700 light years away, is the brightest star within over 1000 light years of Earth, and visually is the sixth brightest star in the night sky.

Sirius is also known as Alpha Canis Majoris. One of the other stars in that constellation, Delta Canis Majoris, is fairly far down the list of bright stars at 37... but it's 1800 light years away. If it were at the same distance as Sirius, it would cast shadows on Earth, and would actually be not just the brightest star, but the brightest object in the night sky about half the time, brighter than any of the planets and even brighter than the Moon from third quarter to first quarter. Eta Canis Majoris is even brighter than Delta, but even further away.

Answer 5

Depending on the distance. If one star is 10 times farther away than another, identical, star, the star that is nearer will seem 100 times as bright. In general, the brightness is inversely proportional to the square of the distance.

This is, assuming no light gets absorbed by interstellar dust or gases.

Answer 6

A star that is twice as far away will be one-fourth (1/2^2) as bright as an identical star that is closer. This is because brightness decreases with the square of the distance.

Answer 7

"inverse square" = 4 times as bright (1.86 magnitudes)

Answer 8

4 times brighter, assuming extinction is negligible (i.e., not much light is lost through interstellar dust and gas). This is an inverse-square law.

Answer 9

4 times as bright.

Answer 10

4