How big would an asteroid or comet have to be to end life on Earth?

NEO=Near Earth Object. The Absolute Magnitude (H) on the bottom axes is a measure of a body’s brightness and is correlated with size. The larger an asteroid is, the brighter it will appear, assuming that all asteroids have the same surface composition (which they don’t, but the assumption is likely good enough to give a rough estimate of the body’s size)

Why don’t planets revolve around the sun vertically?

If we imagine a solar system as originating as a vast cloud that slowly condensed and coalesced into a star and orbiting planets, asteroids, and comets, it stands to reason that all of the bodies would orbit in the same general direction because they all are orbiting as part of the angular momentum of the original cloud.

How do we know that the earth is not the centre of the universe and other objects in the universe do not revolve around it?

 

Is the Universe a sphere? If not, which shape it is? How do we know that?

Artists illustration of the expansion of the Universe

How does The Hubble telescope orient itself in space?

Source: Robert Frost, Quora

The Holmdel Horn Antenna

This is part of an answer by Jon Groubert on Quora:

[…] the science of cosmology was practically born when two guys, Arno Penzias and Robert Wilson, who were working at Bell Labs were trying to find the source of a persistent hum in the background of telephone lines. Bell had tried everything to get rid of this hum, all sorts of experiments, nothing - it was still there.  

In 1964, these two guys were using a type of radio telescope as a detector to see if they could point to something in the sky as being the source.

This is the Holmdel Horn Antenna in Holmdel, NJ. There they are at the bottom of the antenna. But no matter what they pointed at in the sky, they always found the same hum, coming from every direction. Maybe there was something wrong with the antenna? So they went inside the antenna, and found a pigeon nest and pigeon droppings in there. They cleaned it out, killed all the pigeons. The hum was still there, no matter where they looked.  

They hypothesized that what they were observing, this hum, was the leftover radiation from the Big Bang. And they were right!