Will they just not be there

[johnb]

Hi

hope this is not a silly question ?, as some of the things we observe are so old and the light has taken so long to get here i understand what we are seeing may not actually be there, so i assume i could be observing and the thing im looking at could just vanish

Or is it not as simple as that /

John B

[Macavity]

I think it a certainty that much of what we observe will be changed - often considerably, to an observer local to the object! Sometimes even local (to us) BRIGHT objects e.g. highly evolved, or short-lived stars may have tuned into (super-)novae and simply "no longer be there"... at least in their present guise...

And, if you are first to see the process in action, astronomical(?) fame may beckon...

[acey]

Things don't just vanish - stars go supernova or fade away, and either takes time.

But supernovae are observed, and it's something you can hope to see if you observe enough galaxies.

I'm still hoping!

[George]

I have often thought about this, say you are a space traveler and your heading for a star system 100 million light years away. You set the coordinates in your space ship and you go into hibernation for 100 million years (assuming you can travel at the speed of light). A few weeks before you are due to arrive you wake up and take a look out of the window and your star system is not there

It also begs the question how would you navigate these vast distances when reference stars could be popping off randomly and new ones appearing that shouldn't be there?

[MeerkatinBKK]

It also begs the question how would you navigate these vast distances when reference stars could be popping off randomly and new ones appearing that shouldn't be there?

Easy - just remember to turn on the Auto-update option on your GPS (Galactic Positioning System).

---

John yes your hypothesis is correct such that what we look at is what was there a long time ago. For me that's one of the most awe-inspiring facets of astronomy. When we look up at the night sky, we look far back in time.

As Acey states above though, stars will go supernova before they vanish to us. A couple of candidates that may have already exploded are eta Carinae and Betelgeuse. We had a discussion of what may await us in Betelgeuse's case a few months ago on this thread.

Nick

[johnb]

Thanks so im sort of right, so rather than objects disapearing they fade away, in wich case given the number of things out there going through this process is the fade and go concept happening all the time ?

John B

[ollypenrice]

Certainly it is. And of course, the more distant the thing is the greater the likelihood of its having changed or effectively disappeared.

But you don't need to go into space to see this at work. Go and watch a cricket match. Not too close. Watch the bat strike the ball and, when it does, note the delay before hearing the crack. (Sound travels far more slowly than light.) In this case you are simply HEARING smething that is no longer happening.

Olly

[vhbelvadi]

Go and watch a cricket match. Not too close. Watch the bat strike the ball and, when it does, note the delay before hearing the crack.

Olly

Like lightning and thunder, only, a lot more unbelievable.

[johnb]

So as the light from these distant objects do literally fade away and this process is happening as we speak its possibel that if i were observing an area of sky today I may be seeing less than an ancestor observing the same are say 50 years ago ?

Almost like the lights going out

John B

[kniclander]

So as the light from these distant objects do literally fade away and this process is happening as we speak its possibel that if i were observing an area of sky today I may be seeing less than an ancestor observing the same are say 50 years ago ?

Almost like the lights going out

John B

...and your ancestor about 1,000 years ago may have seen the crab nebula as a bright light in the sky in daytime. what do you see now ?

[Macavity]

Indeed so. I think it fair that, on a HUMAN time scale, to first order, object (stars etc.) "disappearance" is pretty much balanced by object formation or, more strictly, recycling! If the future universe is destined for the "big crunch", things may remain approx. unchanged until the "end" of OUR time.

If the universe is destined to last "forever" then very slow particle-physics and quantum phenomena become important. Eventually all light-emitting matter will be consumed by black holes. These in turn "evaporate". Also e.g. protons MAY decay etc. etc. Eventually the whole universe is filled with non-interacting "dark" stuff: photons, neutrinos, and just cools down into a dark, cold, "nothingness".

But these time scales are many orders of magnitude (One followed by hundreds or more zeros) greater than even the current age of the universe. So I sense our SPECIES need not worry overmuch!

[vhbelvadi]

if i were observing an area of sky today I may be seeing less than an ancestor observing the same are say 50 years ago ?

John B

You may be seeing more.

Probably a certain star is a considerably HUGE red giant now compared to what it was thousands of years ago.I suppose that wouldn't make a HUGE difference; but the possibility is there nonetheless.

[Beulah]

It's a fascinating thing to think about - and I was having a hard time explaining this to someone today!!

Found an interesting write up about M1...where there have been records of this object over time, notably the more reliable observations of J.C. Duncan during the 1920s...

Focus On The Crab Nebula

[vhbelvadi]

Interesting link Sam, thanks.

[661-pete]

But supernovae are observed, and it's something you can hope to see if you observe enough galaxies.

I'm still hoping!

I put a question about this on another forum, where one of our more accomplished imagers had posted an excellent animated image of a SN (not his discovery!). It seems that, if we (by which I mean this forum) were the only astronomers in the business, the chances would be fairly good. SN's happen on average about once every 100 years, per galaxy, so if you keep watch on several hundred galaxies throughout the year, you'd be bound to catch a few...

But alas! There are many observatories (and dedicated amateurs) around the world working full-time on SN-hunting. With the very best equipment to back them up. To beat these guys at their game would need an incredible piece of luck. We're not all Tycho Brahe's, I'm afraid!

I have often thought about this, say you are a space traveler and your heading for a star system 100 million light years away. You set the coordinates in your space ship and you go into hibernation for 100 million years (assuming you can travel at the speed of light). A few weeks before you are due to arrive you wake up and take a look out of the window and your star system is not there

Don't forget Special Relativity i.e. time dilation. If you really could go at the speed of light (well, almost) then you wouldn't need to hibernate: your proper time for the voyage might be only a few months...

[brantuk]

Another interesting way of considering this is by asking :

"If something happens millions of light years away right now - how long would it take before we see it from Earth?"

The first sighting may be thousands of years down the line for something that is happening right now in our lifetime (e.g. birth/death of a star, formation/collision of galaxies, ets...). By the time it was sighted, it will have been in existence a long time allready (but invisible to us).