How did we measure the Earth’s distance from Sun for the first time (Near Accurately)
For many of us, it’s a simple number we read in school, and for other many of us including me, it’s a wonderful thing, how we measured something so near accurately without leaving the ground and without using a tape. I always wondered about it until recently I found out how we did it and it amazed me. It was truly a difficult thing, in a way that even when someone knew how to do it, he knew he won’t be able to do it in his lifetime.
It was the 17th Century and Isaac Newton and Johannes Kepler had already done their job. We now knew Newton’s Laws, We knew that planets revolve around the sun. Kepler had taught us that the distances of planets were all related. We knew the distance of Mars from the Sun in terms of Astronomical Units(The distance between the Earth and the Sun), We knew how far Jupiter was from Venus in terms of AU. But the very AU was the missing piece of the puzzle. How far was the earth from the sun in terms of meters?
The key to that missing puzzle was discovered by James Gregorie and Edmond Halley. It was the transit of Venus. We realized how we can measure the distance between Earth and the Sun using geometry based on How the transit of Venus appeared when seen from different locations on earth. Transit of Venus simply means an event when Venus passes directly between the sun and the earth and appears as a black dot on the sun when seen from earth.
But nature had dealt us a tough hand. Venus’s orbit plane is at 3.4 degrees from the earth’s orbital plane. That means that Venus would be in the same plane as earth’s orbit only twice during its orbit and at that time earth may not be in the right spot to see the transit of Venus. It occurs in a pair at a gap of eight years, but once in 120 years or so.
Edmond Halley calculated that it would occur twice in 1761 and 1769 but he won’t be around by then. So he described the method and left it for the coming generation to measure it when the right time comes.
After he was long gone, in 1761 Many astronomers set out on expeditions to different parts of the world to measure the distance as described by Halley. But it was an unlucky time, the world was busy in wars. And many of these astronomers were arrested and could not gather enough data. It was just before 1769, that we realized that it was literally a lifetime opportunity, and they were about to miss out on this. They’d have to wait for another 120 years to see the next transit. That led to one of the first known international scientific treaties. And scientists were able to collect the data in 1769. Jerome Lalande collected all the data and calculated the distance near accurately to 153 million kilometers; that’s off by only 2.5% of the accurate distance we know today(149 million km).
Isn’t that just amazing, even with such less technology, we were able to solve a big piece of the mystery? That makes me even more hopeful about the future. Today with the advent of technology we are able to measure distances of planets far far away from us. And predict many of them to be habitable.
If you like this, please clap 👏👏and share. This is part of my birthday resolution to write one article every month for a year.🐢🐢
✨✨Humankind’s never quenching desire to know the unknown ✨✨