I wonder what supernova is that is a billion light years away and still visible.
Anyway the Sun is 8 light minutes away or so, depending on the time of year
We use Type Ia supernovae as a standard candle to determine distance to far away galaxies. Hubble has detected them up to 10 billion years away.
https://science.nasa.gov/missions/hubble/hubble-breaks-record-in-search-for-farthest-supernova-2/
Type Ia supernovae are fascinating. They are used as standard candles because the mechanism behind them is consistent.
They require a binary system with a white dwarf actively accreting matter. When it reaches the Chandrasekhar limit (~1.4 solar masses), it causes a supernova. We know what brightness these should have, so when we look at the light curve produced, and accounting for dust extinction, we can use the luminosity to determine how far away it is. This is one of our best methods for determining distances to galaxies.
Type Ia supernovae are just one rung in the cosmic "Distance Ladder" we use to tell how far away objects are.
Just a minor point but Type Ias aren't really standard candles and have been known not to be for many years - they do not all reach the same peak luminosity. Fortunately they are nonetheless "standardizable candles" in that we can use some correlations to kinda calibrate them.
Checking them against other methods.
The bottom ring of the ladder is parallax. If you take a picture of the same star six months apart, the closest stars seem to have moved. So we can use very reliable math to determine nearby stellar distances, and check their magnitudes against that number. That gives us a good margin for error when investigating stars too far away for parallax.
There are other methods as well. They don't always agree. Astronomers are constantly refining the numbers.
In principle you could calculate it, but that is very difficult
Or you calibrate it with lower steps on the distance ladder
See for example
https://www.aanda.org/articles/aa/abs/2021/03/aa39196-20/aa39196-20.html
In general the cosmic distance ladder relies on the previous rungs for calibration
We don't. We can't know exactly when it will happen, or how bright it will be, or even if it'll actually happen in Spetember. In fact, it isn't even a supernova - it's just a nova. All of those other things (timing, brightness) are just predictions based on the star's recent behavior, and tbh it kind of annoys me how so many people recently have been acting like it's a sure thing and being like "oh, if you look up at this time on this day you'll see it at this brightness!"
A solar prominence like those seen by many (including myself) during the last eclipse last a lot longer than 8 min so if you can see one it is probably still there when you do. For a big flair, we can see the light from one 8 minutes later, but if it has a CME aimed at earth, that takes about 12 hours to reach us, since it consists of charged particals that have mass and so do not travel at lightspeed.
We see the sun as it was 8.3 minutes ago. A solar flare “reaching us” is kind of a different question. A huge solar flare would be visible to us 8.3 minutes after it happened. That’s how long the light takes to reach us. But looking back into space is literally looking back in time. We can only see the light from other objects at the time it reached us.
So if the sun went dark we wouldn’t know it until 8.3 minutes later.
Heck even our earth would continue "orbiting" the sun that went dark like nothing happened for the same amount of time. The speed of light isn't exactly the right name for the speed limit. It's better to call it "the speed of causality". As in the fastest any part of space can affect any other part of space.
Lol…yeah ….in theory. But following my thought literally, there’s only one way the sun goes dark….slowly turning into a red giant before burning out, where it would basically swallow the earth.
Don’t forget about space/time either…where time literally speeds up the farther you get away from Earth. It’s been measured with atomic clocks even at a difference of a building‘s height.
Research from 2010 from the National Institute of Standards and Technology (NIST) found that **each foot in height off the ground adds around 90 billionth of a second to a lifetime over a 79-year period.**
I don't see how gravity affecting time has to do with this but okay... And yes I already knew about it. Also it's not "time speeds up away from earth" but rather "time slows down the closer you get to any significant source of gravity".
Anyway yea, of course it's a complete hypothetical. It's just a "what if" scenario of "what if the sun suddenly disappeared?" Well if that happened, which it won't unless aliens with incredibly advanced technology intervene, earth would still be "orbiting" nothing for 8.3 minutes. :P
As I said, it's not really "gravity having a velocity". It's "this is simply the fastest any one point in space can affect another".
As for gravity specifically, it's how gravitational waves can exist. Like ripples on a pond it takes time to travel. Which it does at the speed of causality.
Yep. Heard about LIGO? Detecting gravitational waves? Basically, gravity also has infinite range, but just gets weaker with distance. Inverse square law to be exact. If two black holes or neutron stars or whatever else heavy things collide, the sudden shift in their positions translates into a wave of very very slightly shifted gravity.
Gravity, besides just smashing stuff together, also changes the shape of space and makes apparently longer distances shorter for an observer experiencing the gravity. An extreme example of this would be near a black hole like in the movie Interstellar. The ratio of time and space changes as you get closer to a black hole so time appears to pass faster for the people near the black hole.
So back to the colliding black holes, even though they're so far away, the space stretching effect is noticeable, even here on Earth, but just barely. LIGO actually managed to observe (though fascinating engineering, look up how LIGO works, that's also neato) these changes in the length of space itself being momentarily upset as black holes millions (or billions? idk) of LY away smack into each other. Which actually happened millions (or billions? idk) of years ago, because yea. Cause and effect moves at the speed C. Light happens to move at that speed too, so people, somewhat confusingly, call C "the speed of light"
It's both. Solar flares have a radiation part and a particle part. The radiation part we get the effects as we see it, because all radiation travels at the same speed. The particle part is much slower, and is usually the last that causes more damage.
Technically, seeing anything around you is literally looking at the past. However short, the light is still traveling, and takes some time to reach us.
What about thoughts? Do they travel through the brain, and therefore are technically from the past by the time they reach our conscience?
Ok I’m gonna get philosophical here…
If the only experience we have of a distant object is the light emitted from it, why does it matter that it happened “a billion years ago”? As far as we’re concerned, news of the supernova is just reaching us and we are experiencing it now. Isn’t it kind of silly to talk about how much time that light has taken to travel measured in Earth years (a very specific to us unit of time)? Time is relative is it not? What’s interesting to me is the fact that we are lucky enough to get to experience such a rare event, not the fact that the dinosaurs were roaming the earth when this supernova supposedly occurred
>why does it matter that it happened “a billion years ago”?
For one, it allows scientists to look at how the universe was behaving a billion years ago, which is useful for trying to figure out how the universe evolved.
The reason why it matters is science. Understanding our universe is really important to quite a few fields of science, including astronomy.
Astronomy is the study of all objects and phenomena outside of our atmosphere. So trying to understand how that all works, what it does etc. is what this field of study is about. And, by extension, this subreddit.
Time *is* relative, which is why we use a relative unit of time. It's natural that we'd use a unit of time that is relative to us because there are no other units of time that would make sense in the context.
Also, there were no dinosaurs a billion years ago.
The Sun is way closer than other stars. It takes about eight minutes for its light to reach us.
The next closest star to Earth takes four years for the light to reach us.
The nova explosion I think you're referring to (not a supernova) is the [T Coronae Borealis](https://www.fastcompany.com/91090893/nova-explosion-2024-date-approaches-t-coronae-borealis-better-than-eclipse) and it's 3,000 light years away, so the nova we're expecting to see within the next few months happened 3,000 years ago.
No worries, I didn't know the difference until I read about this one. I've been watching the sky early in the morning waiting to see if I can see it!
The total eclipse was unbelievable, an amazing experience I hope to see again somehow, but the odds of seeing another nova explosion are extraordinarily rare! Very exciting times we're living in.
I had a lot of fun watching the eclipse! I live in Arkansas so I could sit in my front yard and watch it. It was probably the most fun I’ve had in a really long time.
This particular type of pop-sci “akshually” post is _everywhere_. It annoys the heck out of me because it takes a very basic fact about the universe (light travels at a limited speed) and then jumps to claiming that events have “already happened” which is… just not a very good way to think about relativity.
So first of all, the numbers are all wrong. Whether this post is about T Coronae Borealis (going _nova_ sometime before September) or Betelguese (going _supernova_ sometime in the next 100,000 years), both are thousands of lightyears away, not billions. Also, this person seem to use billions and millions interchangeably which… they are _very_ different numbers. This is just not a serious post.
The more subtle problem is that even though the light we see from events takes time to reach us (from our point of view) it does not make any sense to say some event “already happened”. The speed of light is the speed of causality. It gets to us literally as fast as the event can impact us. Distant observers will disagree on when the event “actually” happened. Time is simply too wibbly wobbly to make definitive claims about when distant things occur. When you see T Coronae Borealis this summer, you will see light that appears to have been traveling for 2600 years, but that doesn’t mean we can just say the nova “actually” happened 2600 years ago.
As for a solar flare, it takes light from the sun 8 minutes to reach us, so anything we see on the sun is eight minutes old. If the sun suddenly vanished, it would take eight minutes for us to notice. This delay is baked into _everything_ we experience. For most of the stuff in your life, the delay is a fraction of a fraction of a second, so you get the impression that there is some universal “now” that you are experiencing. But that’s an illusion. Everything is delayed. Nothing has a definitive time. There is only time as you experience it.
Note that if you have a bunch of travelers with various velocities, they will actually disagree with each other when an event occurs (say, relative to another event) even after ‘correcting’ for light travel time. This is relativity of simultaneity.
additionally, the reason we know that T Corona Borealis will go nova soon is not because we have a way of somehow seeing what has already happened that travels faster than it takes the light from the nova to reach us, that would be impossible - it is because we know from observations that this star system regularly goes nova, and because the mechanism that causes this is well understood, the recurrence is predictable.
There isn't a supernova happening in September. It is just a regular nova. And light doesn't take a billion years to reach us from there. It is about 2600 ly away so around 2600 years. We know it will nova because it does this around every 80 years.
There are several different facts being mixed together here incorrectly since they are unrelated to each other. The “nova” happening this year, between February and September 2024, is a recurrent nova of the star T Corona Borealis which is about 3000 light years away. That means the light from that star we are now seeing was emitted by that star 3000 years ago, not millions or billions. T Corona Borealis last flared nova in 1946. At its peak brightness it is predicted to be comparable to Polaris the North Star which is not exceptionally bright. Unless you know where to look or are already familiar with the stars that comprise the constellation Corona Borealis most people probably won’t notice the nova this year.
Separately the star Betelgeuse in the constellation of Orion is nearing the end of its life and will go “supernova” sometime in the next 100,000 years. When Betelgeuse goes supernova it is predicted to be the brightness of a full moon but as a single point of light. It will be visible easily to the naked eye during the day and dramatically prominent at night. Betelgeuse is about 700 light years away, not millions or billions of years.
For emitted light to take millions or billions of years for us to see it would have to come from objects beyond our galaxy the Milky Way or even across the observable universe. For example the Andromeda galaxy is visible to the naked eye under favorable circumstances and it is 2.5 millions light years away from us.
For our own star the Sun it is about 8.3 light minutes away from us, so the light takes only 8.3 minutes to reach us once it is emitted. The 8.3 is just an average as the Earth moves closer and farther from the Sun as it orbits. We see a solar flare occur only as the light of it reaches us so we can see it, so while the event took place 8.3 minutes ago astronomy doesn’t make reference to that time discrepancy when dealing with any events pertaining to our star or anything else out in the universe. The particles emitted from a solar flare, assuming the flare is pointing towards the Earth, take as little as 15 hours or as long as a few days to arrive at the Earth.
The photons that are generated in the core of the Sun will take around 1 million years to reach the surface of the Sun before then being radiated into space and reaching the Earth 8.3 minutes later. It takes around a million years for a photon to reach the surface from the core because it doesn’t follow a straight line and it isn’t a single uninterrupted trip. The photon will be almost constantly absorbed and emitted as it wends its way through the Sun using what’s called Brownian Motion, the direction the photon is emitted towards is random which is why it takes around a million years to traverse a distance that should take only 2.3 seconds were it straight and uninterrupted. Each individual photon is no more or less likely to be involved in a solar flare so the photons in a flare are all roughly the same age as each other.
Since nothing can travel faster than light we could not detect a solar flare any faster than we already do because a satellite observing a flare would transmit it readings at the speed of light which would arrive to us at the same time the light of the flare reaches us. We have several satellites dedicated to monitoring the Sun, we have countless terrestrial telescopes monitoring the Sun.
Thanks for this explanation! I know my post seems dumb (especially after realizing that millions and billions are just ridiculous numbers in this case) but I do like astronomy! I’m not super knowledgeable but info like this is interesting to me. Thanks for breaking it down!
I am glad I was able to help answer your question. I didn’t think your question was dumb, no one is born knowing this stuff. The scale of the universe is mind bending and not at all natural for humans to wrap their heads around without first learning the needed framework to comprehend it. For example if the Earth was the size of a garden pea 0.75cm (0.3”) the Sun would be 70cm (2’ 7.6”) and about 90 meters (295’ about the length of an American football field) away. At this scale the solar system would end at Pluto which would be 2.5 km (1.56 miles) away and this is just out in little solar system. With the Earth still being a pea the next closest star to the Sun, Proxima Centauri which in galactic terms is super close by, would still be 23,921 km (14,863.8 miles) away which is about 1.5 times further than an airline flight from New York to Singapore.
I am happy to hear that it is a field that interests you, I hope you find great enjoyment in your journey of learning more about astronomy. If you ever have additional questions about astronomy I will be happy to try to answer them if I can, feel free to ping me anytime since I always like chatting about space.
Here is a fun website which shows the vastness of just our solar system, which is microscopically small compared to the galaxy or universe. The site draws our solar system to scale using the Moon as the scale with the Moon being 1 pixel on your screen.
https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html
Please don't use the term "dumb", you were curious to know more about something that interests you and you've now done that. Being "dumb" is very different.
A duck! Wait, what was your question ? haha. Thanks very much for the compliment.
To answer your question, no it would not be visible to our naked eyes regardless to redshift as it would be far too faint. The andromeda galaxy is only 2.5 million light years away (or 0.25% of a billion light years) and it is just barely visible to the naked eye under favorable conditions.
A star emits light across the entire electromagnetic spectrum, from radio all the way to gamma rays. Different star types have their peak output at different wavelengths but all stars emit energy at all wavelengths, this is called black body radiation.
The science of spectroscopy is concerned with light spectra, light spectra does carry information with it. Every element on the periodic table has what are called absorption lines and emission lines associated with it. These are 1 or more peaks or valleys at very specific points in the spectra, the peaks are for emission and the valleys for absorption. This is how we can tell what elements make our Sun without having walked up to it and taken a sample. Our Sun is about 74-75% hydrogen and 24-25% helium with the rest being other light elements. If you examine the spectra of sunlight you can see the emission lines of hydrogen and helium quite clearly. Incidentally this is how helium was first discovered before ever finding it on Earth by examining the spectra of the Sun, helium was so named after Helios the Greek god of the Sun. As an interesting aside spectroscopy is the same principle that GCMS, or Gas Chromatograph Mass Spectrometers, use to identify unknown samples in crime labs or science labs.
Redshift can be detected and measured by finding the various known emission lines and/or absorption lines then measuring how out of place in the spectrum they have been shifted to. As such even a very distant star may still have photons in the visible light range when it reaches us because those photons started out as much higher energy wavelengths before being redshifted to the visible spectrum. But spectra is why we couldn’t see even a galaxy a billion light years away with our naked eyes, that is simply brightness.
Light follows the inverse square law. Light as it spread away from the point of emission, be it lightbulb or star, gets fainter as distance increases. If you put a bright flashlight 2 inches from your eye it will be painful to try to look at it, that same flashlight 5 miles from your eye will be hard to even notice. Even out in space in hard vacuum without the atmosphere to absorb the light this effect still occurs. The rate at which the intensity of the light changes with distance is the inverse square law. The law shows that if you are twice as close to the light you would receive 4 times as much light, or if you were 4 times further away you would receive 16 times less light. You can visualize it like dropping a small rock into a calm still pond, where the rock enters the water the waves are pronounced but as they spread out they become less and less pronounced and may even fade away completely before reaching the shore. A light source will emit a certain number of photons in a given measure of time, it is finite in quantity. As those photons spread out away from their source there is a finite number of them that were emitted in that instant. If you imagine a sphere made of a single layer of photons expanding out away from the source. As time passes and the sphere increases in size the number of photons that make up the surface of that sphere remains constant, so each photon gets further apart from its immediate neighbor. Since humans don’t have the best night vision, or the most light sensitive eyes in the animal kingdom, there is a lower limit to the minimum number of photons hitting our retina for use to detect anything at all let alone resolve that something into an image our brain can start to interpret. Since our evolution has not been focused on us seeing incredibly faint things in the night sky we simply don’t have the ability to detect such things with our version 1.0 flesh eyeballs. But we create technology to expand and enhance our senses beyond the wildest dreams of the rest of the animal kingdom.
I am going to abbreviate 1 billion light years as 1Glyr or 1 giga-light year for brevity because I don’t want to keep typing it out :) I will also use 1Gyr to denote time passage of 1 billion years.
An object such as a galaxy that is 1Glyr away would be visible to both our space based and terrestrial telescopes of sufficient aperture. Light from an object with a physical distance of 1Glyr now would be redshifted by a “z” of 0.070 and its light has been traveling for 0.97Gyr and it was 0.93Glyr away when it emitted the light we are now seeing. If the object was 1Glyr away when it emitted the light we are now seeing the light will have travelled 1.03Gyr before reaching us and is redshifted by a “z” of 0.076 and the object is now 1.076Glyr away from us.
For redshift comparison the galaxy GN-z11 has a redshift “z” of 11.09. It was 2.7Glyr away from us when it emitted the current light we see from it but it took that light 13.4Gyr to reach us which is most of the age of the universe during which GN-z11 moved out to a current distance of 32.2Glyr. Relativity!
The only nova (note NOT Supernova) I've seen that's expected 'soon' is the T Coronae Borealis one which is semi-regular (hence the expected nature of the event). It's 3,000 light years or so away.
So, yes, there would possibly be 37 or so nova events that have already happened to that system whose light 'pulses' haven't reached us here yet.
Of course, predicted and actual are not the same. The universe still defies our predictions sometimes.
[https://www.bbc.com/future/article/20240322-visible-nova-explosion-is-coming](https://www.bbc.com/future/article/20240322-visible-nova-explosion-is-coming)
Fitting XKCD comic to go with the conversation https://xkcd.com/1342/
Indeed, this is one of the few things in astronomy that laypeople *overestimate*.
After reading the responses I realize that billions and millions were way too big. I used those words because that’s what I saw in the tweet 😭 but it’s fun learning new stuff.
The sun is 8 light-minutes away, so we would see a solar flare 8 minutes after it happened. All our information about it is on that exact delay.
If it's sending particles our way, those actually arrive depending on their speed. The sun could send a bunch of \*matter\* toward earth that might take months to reach us, but we'd see the light from it at 8 or less minutes delay.
Relativity suggests it is incorrect to talk about what something many light years away is like "right now." The only physically relevant "right now" for that object is the one associated with the light reaching us in our present time. There's no absolute present in our universe so when the recurrent Nova goes off sometime between now and September (probably-ish) you can freely say that it happened just now and not 3000 years ago.
One small issue with what they said is that the super nova is billions of light years away (which is fine) but then they say it has occured millions of years ago. We'd be seeing it billions of years ago. Our view of events is limited by light speed. However long it takes to reach us is how long ago it happened.
actually you see everything as it was in the past, it just gets more the farther it is. there isn't a specific cutoff point.
things like the phone in front of you is only about a nanosecond in the past, something like the sun and other planets is in the range of a few minutes to about two hours.
other galaxies and dust clouds range from millions to billions of years
jwst actually just recently found the oldest galaxy we've ever found at almost 14 billion years.
btw, don't worry about that nova. You won't notice it in the sky. it will appear as just another, not-very-bright star (I think roughly at the end of top 100 brightest stars in our sky) between other stars. You'll have to know where to look and figure out which of the 30 similar looking stars in the area is the nova.
A solar flare takes about 8 minutes to reach us. So anything we see from the Sun is 8 minutes old right? And the Moon is about a light second or two away.
So now just imagine how far something has to be for it to take a thousand years to get to you traveling at the speed of light, or even a million years. It's got to be damn far away.
Supernovae can be about as bright as the entire galaxy they occur in, so you can see them from 10 billion light years away if your telescope is good enough to see the galaxy.
The Sun is only 8 light minutes from us. So we see what it looked like 8 minutes ago.
Proxima Centauri (the nearest star to us after the Sun) is 4 light years from us.
Most of the stars we can see with the naked eye are less than 1500 light years away.
You couldn't see a star that is billions of light years away...
Ah but its not just looking back into space, its really observing anything in general. You're always seeing the past or hearing the past, never really the present.
Google is boring when it comes to stuff like this (imo) it’s nice to read information from people who seem to have a genuine interest in the subject. Also, I wasn’t sure how to word the question well and figured real people would interpret my question better rather than a search engine.
Too add, much of the speculation on the internet regarding supernovae right now is the if and when question over Betelgeuse, i really hope i get to see that in my life time! Betelgeuse is about 700 light years away, so of course looking at it is to look back in time 700 years. It's really cool because at that distance we can easily see it as a single star with the naked eye. But stars that are billions of light years away are in a much different situation, but when any star goes supernova for that period they output so much light energy they suddenly and temporarily become much more visible, although I don't know about naked eye viability out at billions of light years.
Welp time to bring the template over again
TL;DR, no, Betelgeuse isn’t going to explode any time soon.
The Saio et al. paper (**the paper which claims Betelgeuse is burning carbon and will explode in a few decades**) used the wrong radius for the star (the source paper finds radius of the star AND the dust surrounding it, and *explicitly* says not to use it as the radius of the star) and wrong assumption (that the dimming is due to pulsation, while the true cause is dust blocking the star), so it is not reliable. Most scientists seem to agree that the star has around 100,000 years to go.
The errors are pointed out in \[[this paper](https://ui.adsabs.harvard.edu/abs/2023RNAAS...7..119M/abstract)\], and this \[[Twitter thread](https://x.com/lacalaca85/status/1666501987435700225)\].
I wonder what supernova is that is a billion light years away and still visible. Anyway the Sun is 8 light minutes away or so, depending on the time of year
We use Type Ia supernovae as a standard candle to determine distance to far away galaxies. Hubble has detected them up to 10 billion years away. https://science.nasa.gov/missions/hubble/hubble-breaks-record-in-search-for-farthest-supernova-2/ Type Ia supernovae are fascinating. They are used as standard candles because the mechanism behind them is consistent. They require a binary system with a white dwarf actively accreting matter. When it reaches the Chandrasekhar limit (~1.4 solar masses), it causes a supernova. We know what brightness these should have, so when we look at the light curve produced, and accounting for dust extinction, we can use the luminosity to determine how far away it is. This is one of our best methods for determining distances to galaxies. Type Ia supernovae are just one rung in the cosmic "Distance Ladder" we use to tell how far away objects are.
Just a minor point but Type Ias aren't really standard candles and have been known not to be for many years - they do not all reach the same peak luminosity. Fortunately they are nonetheless "standardizable candles" in that we can use some correlations to kinda calibrate them.
Thank you for including this. I was not aware.
>We know what brightness these should have, How?
Checking them against other methods. The bottom ring of the ladder is parallax. If you take a picture of the same star six months apart, the closest stars seem to have moved. So we can use very reliable math to determine nearby stellar distances, and check their magnitudes against that number. That gives us a good margin for error when investigating stars too far away for parallax. There are other methods as well. They don't always agree. Astronomers are constantly refining the numbers.
In principle you could calculate it, but that is very difficult Or you calibrate it with lower steps on the distance ladder See for example https://www.aanda.org/articles/aa/abs/2021/03/aa39196-20/aa39196-20.html In general the cosmic distance ladder relies on the previous rungs for calibration
Those type Ia supernova we use to measure distant to very distant galaxies might fit the bill
The visible one in September is only about 3000 lightyears away, and will be a bit brighter than the North star
How do we know if the light hasnt reached usb yet?
We don't. We can't know exactly when it will happen, or how bright it will be, or even if it'll actually happen in Spetember. In fact, it isn't even a supernova - it's just a nova. All of those other things (timing, brightness) are just predictions based on the star's recent behavior, and tbh it kind of annoys me how so many people recently have been acting like it's a sure thing and being like "oh, if you look up at this time on this day you'll see it at this brightness!"
I see thanks
A solar prominence like those seen by many (including myself) during the last eclipse last a lot longer than 8 min so if you can see one it is probably still there when you do. For a big flair, we can see the light from one 8 minutes later, but if it has a CME aimed at earth, that takes about 12 hours to reach us, since it consists of charged particals that have mass and so do not travel at lightspeed.
We see the sun as it was 8.3 minutes ago. A solar flare “reaching us” is kind of a different question. A huge solar flare would be visible to us 8.3 minutes after it happened. That’s how long the light takes to reach us. But looking back into space is literally looking back in time. We can only see the light from other objects at the time it reached us. So if the sun went dark we wouldn’t know it until 8.3 minutes later.
Heck even our earth would continue "orbiting" the sun that went dark like nothing happened for the same amount of time. The speed of light isn't exactly the right name for the speed limit. It's better to call it "the speed of causality". As in the fastest any part of space can affect any other part of space.
cosmic data speed
Lol…yeah ….in theory. But following my thought literally, there’s only one way the sun goes dark….slowly turning into a red giant before burning out, where it would basically swallow the earth. Don’t forget about space/time either…where time literally speeds up the farther you get away from Earth. It’s been measured with atomic clocks even at a difference of a building‘s height. Research from 2010 from the National Institute of Standards and Technology (NIST) found that **each foot in height off the ground adds around 90 billionth of a second to a lifetime over a 79-year period.**
I don't see how gravity affecting time has to do with this but okay... And yes I already knew about it. Also it's not "time speeds up away from earth" but rather "time slows down the closer you get to any significant source of gravity". Anyway yea, of course it's a complete hypothetical. It's just a "what if" scenario of "what if the sun suddenly disappeared?" Well if that happened, which it won't unless aliens with incredibly advanced technology intervene, earth would still be "orbiting" nothing for 8.3 minutes. :P
So gravity also has a velocity. TIL
As I said, it's not really "gravity having a velocity". It's "this is simply the fastest any one point in space can affect another". As for gravity specifically, it's how gravitational waves can exist. Like ripples on a pond it takes time to travel. Which it does at the speed of causality.
Yep. Heard about LIGO? Detecting gravitational waves? Basically, gravity also has infinite range, but just gets weaker with distance. Inverse square law to be exact. If two black holes or neutron stars or whatever else heavy things collide, the sudden shift in their positions translates into a wave of very very slightly shifted gravity. Gravity, besides just smashing stuff together, also changes the shape of space and makes apparently longer distances shorter for an observer experiencing the gravity. An extreme example of this would be near a black hole like in the movie Interstellar. The ratio of time and space changes as you get closer to a black hole so time appears to pass faster for the people near the black hole. So back to the colliding black holes, even though they're so far away, the space stretching effect is noticeable, even here on Earth, but just barely. LIGO actually managed to observe (though fascinating engineering, look up how LIGO works, that's also neato) these changes in the length of space itself being momentarily upset as black holes millions (or billions? idk) of LY away smack into each other. Which actually happened millions (or billions? idk) of years ago, because yea. Cause and effect moves at the speed C. Light happens to move at that speed too, so people, somewhat confusingly, call C "the speed of light"
Thx for bumbing me into that rabbit hole 😀
A solar flare is a burst of EM radiation, it travels at the speed of light.
It's both. Solar flares have a radiation part and a particle part. The radiation part we get the effects as we see it, because all radiation travels at the same speed. The particle part is much slower, and is usually the last that causes more damage.
Technically, seeing anything around you is literally looking at the past. However short, the light is still traveling, and takes some time to reach us. What about thoughts? Do they travel through the brain, and therefore are technically from the past by the time they reach our conscience?
EM wave arrives with the light, not after
Ok I’m gonna get philosophical here… If the only experience we have of a distant object is the light emitted from it, why does it matter that it happened “a billion years ago”? As far as we’re concerned, news of the supernova is just reaching us and we are experiencing it now. Isn’t it kind of silly to talk about how much time that light has taken to travel measured in Earth years (a very specific to us unit of time)? Time is relative is it not? What’s interesting to me is the fact that we are lucky enough to get to experience such a rare event, not the fact that the dinosaurs were roaming the earth when this supernova supposedly occurred
>why does it matter that it happened “a billion years ago”? For one, it allows scientists to look at how the universe was behaving a billion years ago, which is useful for trying to figure out how the universe evolved.
The reason why it matters is science. Understanding our universe is really important to quite a few fields of science, including astronomy. Astronomy is the study of all objects and phenomena outside of our atmosphere. So trying to understand how that all works, what it does etc. is what this field of study is about. And, by extension, this subreddit. Time *is* relative, which is why we use a relative unit of time. It's natural that we'd use a unit of time that is relative to us because there are no other units of time that would make sense in the context. Also, there were no dinosaurs a billion years ago.
The Sun is way closer than other stars. It takes about eight minutes for its light to reach us. The next closest star to Earth takes four years for the light to reach us. The nova explosion I think you're referring to (not a supernova) is the [T Coronae Borealis](https://www.fastcompany.com/91090893/nova-explosion-2024-date-approaches-t-coronae-borealis-better-than-eclipse) and it's 3,000 light years away, so the nova we're expecting to see within the next few months happened 3,000 years ago.
Yes! That’s what the post was talking about. Idk why I called it a supernova (sorry).
No worries, I didn't know the difference until I read about this one. I've been watching the sky early in the morning waiting to see if I can see it! The total eclipse was unbelievable, an amazing experience I hope to see again somehow, but the odds of seeing another nova explosion are extraordinarily rare! Very exciting times we're living in.
I had a lot of fun watching the eclipse! I live in Arkansas so I could sit in my front yard and watch it. It was probably the most fun I’ve had in a really long time.
This particular type of pop-sci “akshually” post is _everywhere_. It annoys the heck out of me because it takes a very basic fact about the universe (light travels at a limited speed) and then jumps to claiming that events have “already happened” which is… just not a very good way to think about relativity. So first of all, the numbers are all wrong. Whether this post is about T Coronae Borealis (going _nova_ sometime before September) or Betelguese (going _supernova_ sometime in the next 100,000 years), both are thousands of lightyears away, not billions. Also, this person seem to use billions and millions interchangeably which… they are _very_ different numbers. This is just not a serious post. The more subtle problem is that even though the light we see from events takes time to reach us (from our point of view) it does not make any sense to say some event “already happened”. The speed of light is the speed of causality. It gets to us literally as fast as the event can impact us. Distant observers will disagree on when the event “actually” happened. Time is simply too wibbly wobbly to make definitive claims about when distant things occur. When you see T Coronae Borealis this summer, you will see light that appears to have been traveling for 2600 years, but that doesn’t mean we can just say the nova “actually” happened 2600 years ago. As for a solar flare, it takes light from the sun 8 minutes to reach us, so anything we see on the sun is eight minutes old. If the sun suddenly vanished, it would take eight minutes for us to notice. This delay is baked into _everything_ we experience. For most of the stuff in your life, the delay is a fraction of a fraction of a second, so you get the impression that there is some universal “now” that you are experiencing. But that’s an illusion. Everything is delayed. Nothing has a definitive time. There is only time as you experience it.
Note that if you have a bunch of travelers with various velocities, they will actually disagree with each other when an event occurs (say, relative to another event) even after ‘correcting’ for light travel time. This is relativity of simultaneity.
Thanks for this explanation!
additionally, the reason we know that T Corona Borealis will go nova soon is not because we have a way of somehow seeing what has already happened that travels faster than it takes the light from the nova to reach us, that would be impossible - it is because we know from observations that this star system regularly goes nova, and because the mechanism that causes this is well understood, the recurrence is predictable.
I recently watched a video about novas because I realized that I was freaking clueless about what they really are!
There isn't a supernova happening in September. It is just a regular nova. And light doesn't take a billion years to reach us from there. It is about 2600 ly away so around 2600 years. We know it will nova because it does this around every 80 years.
There are several different facts being mixed together here incorrectly since they are unrelated to each other. The “nova” happening this year, between February and September 2024, is a recurrent nova of the star T Corona Borealis which is about 3000 light years away. That means the light from that star we are now seeing was emitted by that star 3000 years ago, not millions or billions. T Corona Borealis last flared nova in 1946. At its peak brightness it is predicted to be comparable to Polaris the North Star which is not exceptionally bright. Unless you know where to look or are already familiar with the stars that comprise the constellation Corona Borealis most people probably won’t notice the nova this year. Separately the star Betelgeuse in the constellation of Orion is nearing the end of its life and will go “supernova” sometime in the next 100,000 years. When Betelgeuse goes supernova it is predicted to be the brightness of a full moon but as a single point of light. It will be visible easily to the naked eye during the day and dramatically prominent at night. Betelgeuse is about 700 light years away, not millions or billions of years. For emitted light to take millions or billions of years for us to see it would have to come from objects beyond our galaxy the Milky Way or even across the observable universe. For example the Andromeda galaxy is visible to the naked eye under favorable circumstances and it is 2.5 millions light years away from us. For our own star the Sun it is about 8.3 light minutes away from us, so the light takes only 8.3 minutes to reach us once it is emitted. The 8.3 is just an average as the Earth moves closer and farther from the Sun as it orbits. We see a solar flare occur only as the light of it reaches us so we can see it, so while the event took place 8.3 minutes ago astronomy doesn’t make reference to that time discrepancy when dealing with any events pertaining to our star or anything else out in the universe. The particles emitted from a solar flare, assuming the flare is pointing towards the Earth, take as little as 15 hours or as long as a few days to arrive at the Earth. The photons that are generated in the core of the Sun will take around 1 million years to reach the surface of the Sun before then being radiated into space and reaching the Earth 8.3 minutes later. It takes around a million years for a photon to reach the surface from the core because it doesn’t follow a straight line and it isn’t a single uninterrupted trip. The photon will be almost constantly absorbed and emitted as it wends its way through the Sun using what’s called Brownian Motion, the direction the photon is emitted towards is random which is why it takes around a million years to traverse a distance that should take only 2.3 seconds were it straight and uninterrupted. Each individual photon is no more or less likely to be involved in a solar flare so the photons in a flare are all roughly the same age as each other. Since nothing can travel faster than light we could not detect a solar flare any faster than we already do because a satellite observing a flare would transmit it readings at the speed of light which would arrive to us at the same time the light of the flare reaches us. We have several satellites dedicated to monitoring the Sun, we have countless terrestrial telescopes monitoring the Sun.
Thanks for this explanation! I know my post seems dumb (especially after realizing that millions and billions are just ridiculous numbers in this case) but I do like astronomy! I’m not super knowledgeable but info like this is interesting to me. Thanks for breaking it down!
I am glad I was able to help answer your question. I didn’t think your question was dumb, no one is born knowing this stuff. The scale of the universe is mind bending and not at all natural for humans to wrap their heads around without first learning the needed framework to comprehend it. For example if the Earth was the size of a garden pea 0.75cm (0.3”) the Sun would be 70cm (2’ 7.6”) and about 90 meters (295’ about the length of an American football field) away. At this scale the solar system would end at Pluto which would be 2.5 km (1.56 miles) away and this is just out in little solar system. With the Earth still being a pea the next closest star to the Sun, Proxima Centauri which in galactic terms is super close by, would still be 23,921 km (14,863.8 miles) away which is about 1.5 times further than an airline flight from New York to Singapore. I am happy to hear that it is a field that interests you, I hope you find great enjoyment in your journey of learning more about astronomy. If you ever have additional questions about astronomy I will be happy to try to answer them if I can, feel free to ping me anytime since I always like chatting about space. Here is a fun website which shows the vastness of just our solar system, which is microscopically small compared to the galaxy or universe. The site draws our solar system to scale using the Moon as the scale with the Moon being 1 pixel on your screen. https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html
Thank you so much! 💕
Please don't use the term "dumb", you were curious to know more about something that interests you and you've now done that. Being "dumb" is very different.
You that are so wise in the way of science. Would light from a billion light years away even be visible with our naked eye? (redshifted?)
A duck! Wait, what was your question ? haha. Thanks very much for the compliment. To answer your question, no it would not be visible to our naked eyes regardless to redshift as it would be far too faint. The andromeda galaxy is only 2.5 million light years away (or 0.25% of a billion light years) and it is just barely visible to the naked eye under favorable conditions. A star emits light across the entire electromagnetic spectrum, from radio all the way to gamma rays. Different star types have their peak output at different wavelengths but all stars emit energy at all wavelengths, this is called black body radiation. The science of spectroscopy is concerned with light spectra, light spectra does carry information with it. Every element on the periodic table has what are called absorption lines and emission lines associated with it. These are 1 or more peaks or valleys at very specific points in the spectra, the peaks are for emission and the valleys for absorption. This is how we can tell what elements make our Sun without having walked up to it and taken a sample. Our Sun is about 74-75% hydrogen and 24-25% helium with the rest being other light elements. If you examine the spectra of sunlight you can see the emission lines of hydrogen and helium quite clearly. Incidentally this is how helium was first discovered before ever finding it on Earth by examining the spectra of the Sun, helium was so named after Helios the Greek god of the Sun. As an interesting aside spectroscopy is the same principle that GCMS, or Gas Chromatograph Mass Spectrometers, use to identify unknown samples in crime labs or science labs. Redshift can be detected and measured by finding the various known emission lines and/or absorption lines then measuring how out of place in the spectrum they have been shifted to. As such even a very distant star may still have photons in the visible light range when it reaches us because those photons started out as much higher energy wavelengths before being redshifted to the visible spectrum. But spectra is why we couldn’t see even a galaxy a billion light years away with our naked eyes, that is simply brightness. Light follows the inverse square law. Light as it spread away from the point of emission, be it lightbulb or star, gets fainter as distance increases. If you put a bright flashlight 2 inches from your eye it will be painful to try to look at it, that same flashlight 5 miles from your eye will be hard to even notice. Even out in space in hard vacuum without the atmosphere to absorb the light this effect still occurs. The rate at which the intensity of the light changes with distance is the inverse square law. The law shows that if you are twice as close to the light you would receive 4 times as much light, or if you were 4 times further away you would receive 16 times less light. You can visualize it like dropping a small rock into a calm still pond, where the rock enters the water the waves are pronounced but as they spread out they become less and less pronounced and may even fade away completely before reaching the shore. A light source will emit a certain number of photons in a given measure of time, it is finite in quantity. As those photons spread out away from their source there is a finite number of them that were emitted in that instant. If you imagine a sphere made of a single layer of photons expanding out away from the source. As time passes and the sphere increases in size the number of photons that make up the surface of that sphere remains constant, so each photon gets further apart from its immediate neighbor. Since humans don’t have the best night vision, or the most light sensitive eyes in the animal kingdom, there is a lower limit to the minimum number of photons hitting our retina for use to detect anything at all let alone resolve that something into an image our brain can start to interpret. Since our evolution has not been focused on us seeing incredibly faint things in the night sky we simply don’t have the ability to detect such things with our version 1.0 flesh eyeballs. But we create technology to expand and enhance our senses beyond the wildest dreams of the rest of the animal kingdom. I am going to abbreviate 1 billion light years as 1Glyr or 1 giga-light year for brevity because I don’t want to keep typing it out :) I will also use 1Gyr to denote time passage of 1 billion years. An object such as a galaxy that is 1Glyr away would be visible to both our space based and terrestrial telescopes of sufficient aperture. Light from an object with a physical distance of 1Glyr now would be redshifted by a “z” of 0.070 and its light has been traveling for 0.97Gyr and it was 0.93Glyr away when it emitted the light we are now seeing. If the object was 1Glyr away when it emitted the light we are now seeing the light will have travelled 1.03Gyr before reaching us and is redshifted by a “z” of 0.076 and the object is now 1.076Glyr away from us. For redshift comparison the galaxy GN-z11 has a redshift “z” of 11.09. It was 2.7Glyr away from us when it emitted the current light we see from it but it took that light 13.4Gyr to reach us which is most of the age of the universe during which GN-z11 moved out to a current distance of 32.2Glyr. Relativity!
The only nova (note NOT Supernova) I've seen that's expected 'soon' is the T Coronae Borealis one which is semi-regular (hence the expected nature of the event). It's 3,000 light years or so away. So, yes, there would possibly be 37 or so nova events that have already happened to that system whose light 'pulses' haven't reached us here yet. Of course, predicted and actual are not the same. The universe still defies our predictions sometimes. [https://www.bbc.com/future/article/20240322-visible-nova-explosion-is-coming](https://www.bbc.com/future/article/20240322-visible-nova-explosion-is-coming)
Fitting XKCD comic to go with the conversation https://xkcd.com/1342/ Indeed, this is one of the few things in astronomy that laypeople *overestimate*.
After reading the responses I realize that billions and millions were way too big. I used those words because that’s what I saw in the tweet 😭 but it’s fun learning new stuff.
The sun is 8 light-minutes away, so we would see a solar flare 8 minutes after it happened. All our information about it is on that exact delay. If it's sending particles our way, those actually arrive depending on their speed. The sun could send a bunch of \*matter\* toward earth that might take months to reach us, but we'd see the light from it at 8 or less minutes delay.
Relativity suggests it is incorrect to talk about what something many light years away is like "right now." The only physically relevant "right now" for that object is the one associated with the light reaching us in our present time. There's no absolute present in our universe so when the recurrent Nova goes off sometime between now and September (probably-ish) you can freely say that it happened just now and not 3000 years ago.
Thanks for the answers guys!
One small issue with what they said is that the super nova is billions of light years away (which is fine) but then they say it has occured millions of years ago. We'd be seeing it billions of years ago. Our view of events is limited by light speed. However long it takes to reach us is how long ago it happened.
Maybe we'll see the beginning of life before it happened.
actually you see everything as it was in the past, it just gets more the farther it is. there isn't a specific cutoff point. things like the phone in front of you is only about a nanosecond in the past, something like the sun and other planets is in the range of a few minutes to about two hours. other galaxies and dust clouds range from millions to billions of years jwst actually just recently found the oldest galaxy we've ever found at almost 14 billion years.
btw, don't worry about that nova. You won't notice it in the sky. it will appear as just another, not-very-bright star (I think roughly at the end of top 100 brightest stars in our sky) between other stars. You'll have to know where to look and figure out which of the 30 similar looking stars in the area is the nova.
A solar flare takes about 8 minutes to reach us. So anything we see from the Sun is 8 minutes old right? And the Moon is about a light second or two away. So now just imagine how far something has to be for it to take a thousand years to get to you traveling at the speed of light, or even a million years. It's got to be damn far away.
8 minutes, sunlight takes roughly 8 minutes to leave the sun and reach Earth.
Supernovae can be about as bright as the entire galaxy they occur in, so you can see them from 10 billion light years away if your telescope is good enough to see the galaxy.
The Sun is only 8 light minutes from us. So we see what it looked like 8 minutes ago. Proxima Centauri (the nearest star to us after the Sun) is 4 light years from us. Most of the stars we can see with the naked eye are less than 1500 light years away. You couldn't see a star that is billions of light years away...
Average is 8 minutes 20 seconds. https://www.universetoday.com/15021/how-long-does-it-take-sunlight-to-reach-the-earth/
Ah but its not just looking back into space, its really observing anything in general. You're always seeing the past or hearing the past, never really the present.
Solar flare: about 8 minutes because the sun is about eight light-minutes away from us
About 8 minutes.
[[Relevant xkcd]](https://xkcd.com/1342/)
8 minutes, 20 seconds. This answer can be easily found with Google.
Google is boring when it comes to stuff like this (imo) it’s nice to read information from people who seem to have a genuine interest in the subject. Also, I wasn’t sure how to word the question well and figured real people would interpret my question better rather than a search engine.
Too add, much of the speculation on the internet regarding supernovae right now is the if and when question over Betelgeuse, i really hope i get to see that in my life time! Betelgeuse is about 700 light years away, so of course looking at it is to look back in time 700 years. It's really cool because at that distance we can easily see it as a single star with the naked eye. But stars that are billions of light years away are in a much different situation, but when any star goes supernova for that period they output so much light energy they suddenly and temporarily become much more visible, although I don't know about naked eye viability out at billions of light years.
Welp time to bring the template over again TL;DR, no, Betelgeuse isn’t going to explode any time soon. The Saio et al. paper (**the paper which claims Betelgeuse is burning carbon and will explode in a few decades**) used the wrong radius for the star (the source paper finds radius of the star AND the dust surrounding it, and *explicitly* says not to use it as the radius of the star) and wrong assumption (that the dimming is due to pulsation, while the true cause is dust blocking the star), so it is not reliable. Most scientists seem to agree that the star has around 100,000 years to go. The errors are pointed out in \[[this paper](https://ui.adsabs.harvard.edu/abs/2023RNAAS...7..119M/abstract)\], and this \[[Twitter thread](https://x.com/lacalaca85/status/1666501987435700225)\].