Definition: The angle formed by an object at a given external point
Drag the orange dot representing the observer's eye, or the base of the flagpole. Note how the angle subtended by the flagpole to the observer's eye varies with distance.
The moon subtends an angle of approximately 0.54° (32 arc-minutes)
to an observer on the Earth.
Of course, the moon's orbit is not constant or exactly circular, so this varies a little. But not by very much.
If you hold up your thumb at arm's length, you can easily cover the full moon.
This means your thumb subtends a larger angle to your eye at arm's length
than the moon does at 380,000 kilometers.
The sun, on the other hand, subtends an angle of approximately 0.52°
(31 arc-minutes) to an observer on the Earth.
This is a striking coincidence. By sheer chance, it is almost the same as the angle subtended by the moon.
This is why, during a solar eclipse, that the moon almost exactly covers the sun.
A Solar Eclipse
Because they both subtend nearly the same angle to the earth, when the moon gets between the sun and the earth, it covers the
sun almost exactly, causing a solar eclipse. During the eclipse a thin glittering ring can be seen around the disk.
This is caused by hot glowing gases and other material streaming into space from the sun.
The sun is about 150,000,000 kilometers from the earth,
so clearly the sun must be vastly larger than the moon.
Not to scale
While you are here..
... I have a small favor to ask. Over the years we have used advertising to support the site so it can remain free for everyone.
However, advertising revenue is falling and I have always hated the ads. So, would you go to Patreon and become a patron of the site?
When we reach the goal I will remove all advertising from the site.
It only takes a minute and any amount would be greatly appreciated.
Thank you for considering it! – John Page
Become a patron of the site at patreon.com/mathopenref
Other angle topics
(C) 2011 Copyright Math Open Reference. All rights reserved