How do scientists predict celestial events? I mean, if the solar eclipse is happening today, how do they know it happened XX years ago or that it will happen XX years later?
I am not talking about simply predicting a solar eclipse but rather specifically how long it’s been since this exact same type occured.
In: 6
First you start with observations. People watched the skies for centuries, out of both boredom and religious intent. They meticulously recorded events.
After a while it became apparent that major events weren’t simply random – solar and lunar eclipses seemed to come in clumps, and always correlated with full or new moons.
With enough data on this, medieval astronomers could start to work out the mathematics behind it – the Earth and the Moon have very predictable orbits and will repeat the same cycles over and over again.
Today the orbits are well modeled, and we can predict eclipses with extremely high accuracy.
All celestial events occur in cycles, so whenever a cycle is complete, the same events occur again. In case of solar eclipses, the cycle is about 18 years (called a “saros”). This is a period of time in which the Moon and the Sun both complete whole numbers of their own cycles, setting them to repeat the same events all over again.
You may have observed that the sun rises every 24 hours. You think it’s safe to predict that it will rise again tomorrow. Maybe you talk to people that have noticed it before you and they confirm your suspicion: the sun has been rising everyday in the past too.
The sun rising is a cyclical celestial event like any other.
Modern scientist can do simulations and stuff, but long ago people could figure that out relatively easily.
People write down stuff like seeing a solar eclipse it is pretty memorable.
If they write down when they saw an eclipse it gets relatively easy to see a repeating pattern.
If you pay a lot of attention you notice things like all solar eclipses happening during a new moon and all lunar eclipses happening during a full moon.
Next you notice that sometimes the moon during a new moon is above the sun and sometimes below it and that it only gives you an eclipse when it is directly in front of it. You can watch the moon move up and down in relation to the sun and you figure out that there are two repeating cycles involved, one of the phases of the moon and one of the moon going up and down. When both the moon going through a node and the moon going through a full or new moon coincide you get an eclipse.
It doesn’t take much to predict when there will be a new moon and a full moon many years in advance and figuring out the other bit also just requires a bit of paying attention.
Then the rest is just a bit of math.
There is an 18 year cycle (223 times the moon through its phases) after which the pattern for possible eclipses repeats. So once you know about enough eclipses happening in the past you can just extend the known pattern forward even without understanding the physics or geometry or math behind it.
The Eclipse today matches the one that happened on October 14 in 2004 and the one that will happen November 4, 2040.
You can just always go backwards or forwards 18 years and 11 days (plus or minus a day depending on how many leap years there were).
Latest Answers