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7

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 satellite is pulled around the Earth. If the object is a single small particle, that's almost the end of the story. Gravitational radiation and the precise ...

7

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 nonetheless persist. Statistically, by 500,000 years from now, we should have been hit by an asteroid 1 km in diameter, and 100,000,000 years from now, we should have ...

6

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 integrated over the volume of the plasma. $${\rm EM} = \int n_e^2 \ dV$$ The flux of optically thin emission from a plasma (e.g. thermal bremsstrahlung) is then ...

5

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 brightest being "stars of the first magnitude". When more precise measurement became possible, this scale was retained, and extended into the negative numbers for ...

3

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 you won't see them anymore like it used to. Years ago, if the local time was midnight you could almost be assured no satellites would be visible but that's not ...

3

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 number 30774) passed very close to Arcturus at 23:40 pm from your location (45.7288° N, 24.3784° E). Note that I am assuming that your time is 3 hours ahead of ...

2

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.

1

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 when it reached wires/conductors at the Earth's surface the opposite effect would take place: ie the EM radiation would result in the flow of charged particles ...

1

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 established shower; birds (yes, sometimes light-coloured migrating birds reflect city light from their bellies).

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