Recent comments in /f/askscience

rootofallworlds t1_jd2tqxt wrote

Reply to How do we know if a comet will hit earth? by VloeibaarHout

This is known as orbit determination.

https://en.wikipedia.org/wiki/Orbit_determination

A telescope can observe what direction something is in, but cannot directly measure the distance. But because an object's motion depends on its distance from other masses (mainly the sun), three observations at different times are sufficient to determine the orbit. Newton worked that out for the special case of a parabolic trajectory and later scientists refined the mathematics and extended it to all orbits.

The observations have error bars, which means the orbit determination also has error bars. Observations over a short period of time tend to result in less precise orbital information than observations spaced further apart, and extra observations are good to have. (And in some cases, we actually have radar distance measurements.) The error bars on the orbital information mean that a prediction of the future position of the comet is less precise the further into the future it is, and if the comet will pass a planet close that amplifies the errors. For small bodies like comets and asteroids non-gravitational effects, mainly relating to solar radiation, can perturb the orbit and they are hard to predict. All these factors mean don't usually know for certain that an asteroid or comet will hit or miss Earth, but instead you read things like a "1 in 100 chance of impact in 20xx".

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the6thReplicant t1_jd2hj6h wrote

Reply to Do we know where is the center of big bang located presently in reference to earth? by MagnetCarter

Imagine you’re in a big ocean. You look out to your horizon. You realize that you’re in the center of the circle of that horizon.

Does that imply you are in the precise middle of the ocean? No.

You are always center of the horizon since you yourself made the horizon.

We are at the center of the universe we see.

Or.

The universe we live on is the surface of an inflating balloon. Where is the center of that universe on the surface of that balloon. It’s a meaningless/impossible question to answer other than saying the center is where you are or there is no center.

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Any-Broccoli-3911 t1_jd2fxr2 wrote

Reply to Animals with more neurons outside the brain than inside? by placidbeans

Most invertebrate have an anterior ganglia or central nervous ring that are considered equivalent to the brain, but have typically less than half the neurons.

It's also the majority of animals because invertebrate species are much more numerous than vertebrate.

Cnidaria (Jellyfish, sea anemones, coral) and sponges have neither, so all their neurons are outside their non-existent brain.

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Krail t1_jd2bwak wrote

Reply to comment by viscence in Do we know where is the center of big bang located presently in reference to earth? by MagnetCarter

There was a post a couple days ago where someone was staunchly asserting that space is not actually expanding and that objects really are moving away from one another kinetically, with multiple citations on the subject (which I didn't look too far into). There was a bit of discussion and a couple people agreed with them.

This was the first I'd heard about that. All modern material I've ever seen on astrophysics (the last twenty five years or so?) talks about the universe expanding.

How solid is the scientific consensus on this subject? Is it actually contentious at the moment, or was this person stating an belief that is currently kind of fringe?

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K-a-v-a-u-n t1_jd26ps0 wrote

Reply to Do whales and sharks etc. have any sense of their location in the ocean, or do they live a life simply “lost at sea”? by Legitimate-BurnerAcc

There are orcas (I think) that are described as "residents" they stay in a more or less defined area where other orcas travel. There is also a shark species that sometimes meet up at a certain spot. It is hard to find a all fitting answer but the behavior of some suggests that they are aware of locations like, "where I am " and "where I want to go /be"

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