# Light speed moving objects -- What would it look like?

Hello community,

First of all I want to apologize if what I'm about to post is a complete nonsense, I have to admit that my knowledge in physics and futhermore astrophysics is close to NULL, but from a few years back I've been wondering some things but I didn't have the chance to discuss about it with an expert in the topic.

Now without further delay, this is my question.

Imagine for a second the following scenario:

* The sun explodes
* The explosion travels far enough to reach Earth.
* The explosion travels at the speed of light
* Discard any death due the explosion, lack of sun, etc.

Now being aware that the information travel from the sun to Earth takes about 8 minutes we have to assume that we will realize that the Sun started exploding 8 minutes after it began, right?

Here comes the real question... How would it look like?

The question is because, assuming the explosion travels at the speed of light and so does information, we would stsrt seeing the sun explode at the same time we get hit by the explosion, therefore we would look at the explosion first, but fron what distance? And how would the rest of the explosion look like? It would look as a normal event developing in a secuence since we already saw the end od it and the following thing happens:

Sun explodes (SE): 8 minutes until we realize from Earth
Explosion half way through: 4 minutes until we realize from Earth

When the explosion is 4 minutes away, so is our realization of the sun explosion.

I hope I was able to communicate properly the idea, and I would be thankful for any person who can help me out with this.

berkeman
Mentor
Welcome to the PF.

Radiation and light from the explosion travel at the speed of light in a vacuum. The actual matter from the explosion travels slower than the speed of light (no material object can travel at the speed of light in a vacuum).

davenn
Most CMEs here at Earth hit about 3 days after the event on the sun's surface that caused them. Even if there were to be a nova type event, I would assume that yes, there would be a brightening, but one would likely see indications of the imminent explosion, such as heavier outgassing and sunspots to a sudden shrinking in the size of the sun, perhaps a dimming at the same time as the photon flux is no longer enough to hold up the mass, so there may be a period of minutes to hours where one sees changes in the surface of the star pulling itself inwards even before the explosion happens. Once the explosion does, then, as with atomic weapons, the light pulse will pretty much evaporate anything, including oceans, rocks and possibly the entire planet evaporating and exploding apart under the heat pulse. In that case there would be little to see aside from a sudden rushing brightness that just keeps increasing and increasing, well beyond what an observer could survive. This brightness would taper off but the mass of the star would be not that far behind the light/heat pulse and would create a second brightening and the huge masses of what was a star passing through the space where a planet Had been and when it cooled, the dust from the planets and asteroids and comets of that system would be a part of the planetary nebula formed.

(added) There have been several science fiction stories that examine this idea, one of them had a large flare happen while people were watching the Moon at night, and the Moon suddenly got Very Bright, Much brighter than normal, and there came the shock wave and other devastating effects, but it was just a huge flare and not a Nova type event. However, by reading a lot of how stars are formed and how they end their lives (as much as we presently know) I think I have given a fair description of what might be seen. It is certainly not something that could be hidden, unless the heating caused massive cloud cover somehow, but that is possible via several mechanisms too.

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PeroK and berkeman
That being said, the likelihood of the Sun doing a Nova type event is considered to be very unlikely isn't it?
Seems to be a fairly average stable yellow star about half way through the process of H to He fusion.

Steelwolf and davenn
davenn
Gold Member
2021 Award
That being said, the likelihood of the Sun doing a Nova type event is considered to be very unlikely isn't it?
Seems to be a fairly average stable yellow star about half way through the process of H to He fusion.

yeah.
The sun is on its path to becoming a red giant

Steelwolf
Fervent Freyja
Gold Member
The sun is an explosion itself.

Wasn't a movie made about the solar flare catastrophe? A mentally disturbed family lived out their days knowing the earth would be struck by a deadly solar flare? Sad.

A large enough solar flare could kill much of the life on the planet in one sweep, many remaining near the surface would die not long after, but still the earth would not be destroyed totally. The earth would likely continue to burn and be in a state of chaos. There would be many underground resources and surviving organisms to maintain a life cycle in the future (even if it takes a few million years to recover). This is believed to be a cause of some past extinction events.

We would have a warning a few days in advance of such a flare hitting earth. The sun is under constant surveillance all over the world, as even slight flares can impact flights.

Steelwolf
davenn
Gold Member
2021 Award
A large enough solar flare could kill much of the life on the planet in one sweep

maybe but nothing has occurred like that so far in recorded history

This is believed to be a cause of some past extinction events.

and in all my geology and astronomy studies, have never heard that one before
do you have a good reference ?

Dave

Fervent Freyja and berkeman
Fervent Freyja
Gold Member
and in all my geology and astronomy studies, have never heard that one before
do you have a good reference ?
Dave

Probably because most of the work has been more recent, here's one giving evidence for a solar flare causing the Pleistocene Mass Extinction. There are more papers on solar flares causing of a few other extinction events. I can't read through them all at the moment, but if you are interested, have a go!

davenn
davenn
Gold Member
2021 Award
Probably because most of the work has been more recent, here's one giving evidence for a solar flare causing the Pleistocene Mass Extinction. There are more papers on solar flares causing of a few other extinction events. I can't read through them all at the moment, but if you are interested, have a go!

thanks for that, interesting reading and a small extinction event I was unaware of. It seems as tho a very large flare is one possible cause. Others including overkill by man, climate ( the ice age) and an impact. and lots of objections to all 4.
One interesting feature seems to be that it was aimed primarily at large mammals

will have to do some more searching and reading

Dave

Fervent Freyja
Fervent Freyja
Gold Member
One interesting feature seems to be that it was aimed primarily at large mammals
Dave
You're welcome!

Yes, endothermic organisms, mammals and birds, are the most vulnerable during extinction events- they are the most likely to be out in the open and exposed. Smaller mammals tend to live out their lives in shelters that have better protection. They mostly have higher survival rates because the probability of them being out in the open during an event is just considerably less than that of large mammals. Organisms residing in deep water or earth have even higher chances of surviving some types of extinction events.

berkeman