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8 votes
Accepted

How does a Super-Massive Black Hole 'flare'?

The flare happens just outside the black hole. Matter which aproaches a black hole but not perfectly straight on doesn't fall into it immediately. It gets pulled around the black hole, just as a ...
  • 9,958
7 votes
Accepted

What cosmic disaster is most likely to happen?

Asteroid impacts are a possibility, but a killer asteroid typically affects the Earth every few dozen million years. This would probably destroy all life as we know it, but life will probably ...
  • 895
7 votes
Accepted

What is "emission measure"?

Emission measure is (usually) used in X-ray and EUV astronomy, though I suppose also in cases of optically thin radio emission. It is defined as the square of the number density of free electrons ...
  • 124k
5 votes
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Magnitude, satellite flare and the Heavens Above app

The astronomy "magnitude" scale works backwards: smaller numbers indicate brighter objects. Back in the days before precision measurements of brightness, stars were categorized by eye, with the ...
  • 3,031
4 votes
Accepted

Events I cannot explain

Both of these sound like satellites reflecting the Sun, even the first one which didn't fade. There are so many satellites now with unusual orbits that being close to midnight in time doesn't mean ...
3 votes

Can a solar flare destroy every electronic item on earth?

Can a solar flare destroy every electronic item on earth? Extreme Limit Let's start with an extreme upper limit, a supernova. So we know that a typical supernova will not eradicate our atmosphere, ...
3 votes

5 sec flare near Arcturus

My first thought is that you saw a flare from a satellite, meaning a favorable reflection off of a solar panel or something. I use the software "Heavensat", and it shows the satellite Nextsat (Norad ...
  • 7,322
3 votes

What would be the effect of a large solar flare on motor vehicles?

Never drive a car which is larger than a football field during a solar storm Otherwise, don't worry about it. The answer to Does a geomagnetic storm visibly deflect a compass? shows the plot below ...
  • 30.6k
1 vote

Travelling, flashing Star?

It is highly likely that what you have seen is an Iridium communications satellite. Because of the material covered, it can reflect sun light and appear very bright and sometimes flashing.
  • 181
1 vote
Accepted

Unknown moving objects

Converting comment to community wiki Possibilities: Aircraft lights (but only if non-blinking); genuine satellites/old launch stages not in the database; random ("sporadic") meteors not part of an ...
1 vote

What is "emission measure"?

@tefalya Somebody told me "EM is the integral of electron density squared over the emitting volume. In collisional ionized plasmas, it gives the amount of material emitting at a given temperature. ...
  • 2,955
1 vote
Accepted

Can a solar flare destroy every electronic item on earth?

Here's the how: very energetic charged particles interact with the Earth's magnetic field, and when they do so they emit electromagnetic radiation. If the energy of this radiation was high enough then ...

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