# How is it possible to know how far the sun is (a place noone has ever been us humans dont even know the circumference of our own earth?

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• It is calculated using the Earth's shadow on the Moon. Knowing the Earth's radius and circumference, and them by using Trigonometry and Similar Triangles.

To correct you, humans DO know the circumference of the Earth. It was calculated by a Classical Greek mathematician, Eratosthenes,  some 2500 years ago.

• Right!  "Us" humans don't know the circumference of our own earth (not to mention other people's earths).  In fact, some of us humans don't even know our you-know-what from a hole in the ground.  But I'm not mentioning any names, Nick.

• One of the most fascinating things about science history is how the ancients figured out things.

It was very simple to calculate the size of our Earth by measuring the angle to the Sun from a measured distance North to South on a given day.  Once the size of the Earth was determined the distance to the Sun could be calculated by setting up a future date to measure the suns position at a known distance apart and determine it's distance.

• There are lots of scientific ways to calculate the circumference of the earth the Greeks did it long ago

The distance to the sun can be calculated  one way is to measure the angle of the sun from different locations on earth at the same time

• How is it possible to be as willfully ignorant as you are ?

• We do know Earth's circumference and have done for around 2000 years.

• It is around 93 Million miles to the Sun

Now bear in mind that the Diameter of the Sun is 1.3 Million miles

Earth is around 12, 000 miles

So when you look at it, Diameters in Scale to the Distance is basically Negliable in the Scale of Space

That is why we use AU, Light Years and Parsecs for the distance to Stars

• The Sun is about 93 million miles from Earth. ... To calculate the distance to a star, astronomers observe it from different places along Earth's orbit around the Sun. If they measure the object's position several months apart, their "two eyes" will have a separation of well over 100 million miles!

Historically, the first person to measure the distance to the sun was the Greek astronomer Aristarchus around the year 250 B.C. He used the phases of the moon to measure the sizes and distances of the sun and moon. During a half moon, the three celestial bodies should form a right angle

We have known the exact circumference of the Earth for a very long time.   The Greeks figured it out 2500 years ago

• It's actually a fascinating story... The mechanics of it are very clever, and it was a transit of Venus that got us within ballpark.  Sir Edmond Halley knew he wouldn't live long enough for another transit of Venus (they're relatively rare) - so, he wrote instructions on *how* to do the measurement to future astronomers...

https://phys.org/news/2015-01-distance-sun.html

• Is this site getting dumber ?