Optics
Learning physics
and chemistry
easily and freely - Science for elementary school, middle school and
high school
Free online optic lesson for elementary school, middle school and high school.
Propagation of light
Light and distances
At human scale light seems to propagate in very short times but it's different at universe scale.
The time that light needs to propagate is even used to compare distances between stars and planets.
Here are some significative examples:
The closest heavenly body to the Earth is the Moon at roughly 380 000 km. Light emitted by the Moon takes 1,3 second to reach the Earth.
The Sun is roughly at 150 000 000 km from the Earth and its light propagates for 8 minutes and 20 seconds to reach the Earth.
As for the stars that are much farther from the Earth, their lights have to propagate for several years before to reach the Earth: for instance, light from Proxima Centauri travels for 4,2 years before we can see it.
Thus, distances between stars are usually expressed in " light-year ": a light-year is the distance that light travels in one year.
A light-year is about 1013 km.
As for the solar system its distances can also be expressed in light-second, in light-minute or even in light-hour.
| Science class |
| Optics lessons |
Light sources - Types of light sources - Why can we see objects ? Propagation of light - Rectilinear propagation of light - Beams of light - Speed of light - Light and distances Shadows, lunar eclipses and phases of the moon - Formation of shadows - The Moon and eclipses Colored lights - color of objects - Decomposition of white light - Colored lights - Color of objects Image formation - Thin lenses - Thin converging and diverging lenses - Image formation by thin lenses - Vision and eyes |
|
|
©2021 Physics and chemistry