Space is really big, even just in our own solar system. So how can astronomers be sure they’re looking in the right place at the right time to catch an asteroid, even when they don’t know it will be there? Is it just luck? Or is there some kind of educated guesswork going on?
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Well, the short answer is. They dont.
We’ve been very very lucky so far. Only very few asteroids are detected, since we can only watch so much of the sky at once. And even then funding is a huge problem since it’s not a problem thats very high in priority for governments even though the economic damage would far outweight just about any other funding goal. The russian Chelyabinsk meteor in 2013 for instance was tiny and caused damage to over 7000 houses despite it being incredibly far away from them basicly in the middle of nowhere.
And just recently one came from an absolute blind spot in the direction of the sun and surprised us. It was on the same day on which we were expecting a asteroid to come from the other side.
Yes, it is just luck.
No, its hard to say where they’re comming from so you cant exactly aim for them ahead of time. You just scan as much of the sky as possible, as many times as you can. This is why the Aricibo Obervatory being dismantled is such a loss. It was basicly our space radar for a lot of these things.
That said. Dont panic. Chances are slim we’ll get hit. If we do, it’s probably not a planet killer.
You find asteroids in our solar system earth by taking photos of the same point of the sky at different times. The stars far away will not move so any point of light that has moved is close. With multiple observation and the using earth moment around the sun, you determine the distance and it orbit.
The first large asteroid was discovered just like that in the 19th century but without photographs so you had to do draw what you observed on paper. Ceres that is the larges asteroid was found that way in 1801. Not a lot was discovered this way
Later you get photographic plates and then film more was discovered.
The majority of asteroids in our solar system has been discovered recently with digital cameras, robotic telescopes, and software that analyze the data
So you systematically take images of the sky and compare them over time.
One of the programs can be found [https://cneos.jpl.nasa.gov/about/search_program.html](https://cneos.jpl.nasa.gov/about/search_program.html)
When looking for undiscovered asteroids, you look at a part of space for an extended period of time, and just look for anything that moves. That does require a significant amount of luck, since it requires the asteroid to be in the field of view when you’re looking, but that element of luck can be reduced by increasing the amount of time you spend looking, increasing the amount of area you look at, and focusing on places where asteroids are more likely to be.
Once an asteroid is discovered, it can be tracked. Asteroids move in predictable ways, so if we measure it’s position and speed accurately, we can know where it will be in the future so we can find it again.
Astronomers do not know in which direction to look in order to find asteroids. So they are looking in evey direction and just hope there is an undiscovered asteroid there. Most of the asteroids are in the asteroid belt so it is possible to limit the search area to the nearest part of this belt for a greater chance of discovering asteroids. However some of the most interesting asteroids to study is not in the asteroid belt so it can often be more valuable to look elsewhere. And of course you often run into problems such as terrain blocking parts of the sky or that the moon, planet or bright star is in the way which further limits the areas of the sky that can be searched at any given time. But best options for finding asteroids is still to just point the telescope in a random direction and hope.
Excuse me, but I feel on a sub like eli5 somebody needs to point out that space is not, in fact, massive … it is the exact opposite.
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