The further we look into space the further back on the cosmic clock we are observing.

Thank you for making the science of observing space a joke. Hope it was meant as such. A clear waste of time. The only star concerning me is the sun. If it goes I'll know 8 min. later. Nobody give me the exact travel time. Even that would be wasted on me.

The entry question was asked in all seriousness so let me be honest. To look at light were the source has vanished 50 billion years, or three days ago for that matter, is like watching paint dry, just faster. It still takes that time to conclude "something" what ever that may or can or could have been.

To think of storing this "event" of a light pulse is so incredibly useless, impractical and not achievable at a rational level that it is taking my breath away. It really did for a moment.

"But we have no means of knowing that a particular star still exists, until we see a supernova, or other means of detecting the alteration."

And with what conclusion? The very exiting pictures (computer enhanced) of these actions of light and its source are the only thing coming out of it for human race. Maybe there are some others discoveries which are still being revised and disputed or revised again and the next time not so much talked about any more. Only by the few which have made this their life's quest. It should be an art form and not a science. Light traveling? Bloody boring. Light reflecting off things is all we will ever see.

Sound traveling (Music) is more of a "to be studied" subject. It can be stored, repeated, is universal and includes the aspect of light in some ways. While music is absorbed it rejuvinates and will never die. The lights I see when I listen to Beethoven's 9th Symphonies (yes the plural because the light is stored and can be repeated as I mentioned) or Voodoo Child, we all know by who.

'To wish upon a star' land. I'll stick to what is in the here and now. Not as boring as some. Sorry all you guys in the "perfect know" but you are wasting time. No not mine or yours it's our time. Foot in mouth disease? Rather tongue in cheek.

The further we look into space the further back on the cosmic clock we are observing.

Back to were we came from. Some day. Ky.

G'day gals, guys, gurus & ky

• The only star concerning me is the sun. If it goes I'll know 8 min. later.

I could be wrong but I get the impression you are not that interested with astronomy and cosmology.

On the subject of stars that are of concern, other than our Sun which we are completely dependent on, the next one that is worth close monitoring is η‑Carinae (eta Carinae) which is located in the diagram below at the centre of the small dashed circle near the centre of the image.

The easiest way to fine η-Carinae is to look for the southern cross first as shown by the red cross in the lower right quadrant of the image

η-Carinae is a super giant star that is pert of the milky way that is about 7,000 light years away from us and it at the end of its life. Currently η‑Carinae has a light intensity of 6.21 so you will need a telescope to see it, however it has varied in intensity from 7.9 to -0.8 over the last century or so.

The reason η‑Carinae is worth monitoring is that it is at the very end of its life as a star and could go supernova at any time. Late last year a similar star in distant galaxy blew itself apart in what astronomers described as the most energetic event ever witnessed. For some time it was emitting more energy and light than the remaining billion or so stars in the galaxy.

Statistically a galaxy the size of our Milky Way would see a supernova event every 100-200 years ant that means we are somewhere between 100 and 300 years overdue and η-Carinae is definitely behaving in a manner that is exactly what you would expect immediately prior to it going super nova.

So, what can we expect to see if η‑Carinae blows itself to oblivion. For observers in Australia η‑Carinae is always above the horizon so it will be visible 24 hours a day. The intensity and energy that is expelled would make it only second to the Sun in brightness and produce enough light to make it possible to read by but that's not what is of most concern. Large supernova events like this usually produce a very intense burst of γ-radiation and there is a chance that the intensity of γ-radiation that reaches the ground cold be of great concern.

Then there are the asteroids and comets that cross Earth orbit. Admittedly these are technically not stars but many people will refer them to stars an the word comet comes from the Greek komētēs which loosely translates to a long‑haired (star)

So, if you aren't concerned with any other star than our Sun then I would suggest reassign your priorities. The risk to your general health and wellbeing from other extraterrestrial events is slim but it isn't zero and considering the possible consequences requires serious consideration.

• Nobody give me the exact travel time. Even that would be wasted on me.

Since the distance between the Earth and Sun varies from 147,098,074 to 152,097,701 km but that is centre to centre and you need to allow for the equatorial diameter of Earth 6,378.1 km and the Sun's 1,391,000. Now, the speed of light in a vacuum is 299,792,458 ms-1 so the time it takes for the light leaving the surface of the Sun

Therefore we can calculate the time for light to travel from the surface of the Sun to the surface of the Earth as follows.

However, this is only valid when the Sun is directly overhead. Depending on the elevation of the Sun the distance the light needs to travel will be increased by up to half the diameter of the Earth. We can then calculate the additional time as follows:

So, to the nearest millisecond the time it takes for the light from the sun to reach the surface of the earth varies between 8 minutes 8.438 seconds and 8 minutes 25.119 seconds plus up to an additional time that is calculated by the cos of the apparent elevation of the Sun above the horizon multiplied by 11 milliseconds.

Is that sufficiently accurate or would you like me to calculate the delay to the nearest microsecond or nanosecond?

I ask because calculating the delay more accurately than milliseconds requires taking into account parameters like the density of the Earth's atmosphere, the Sun's corona and any matter that may be in the space between the Earth and Sun. The amount of matter in space between the Earth and Sun can vary quiet dramatically especially if there has been a recent Coronal Mass Ejection.

PS Clearly my new year resolution to be less of a cynical sod wasn't worth the toilet paper I wrote it on.

Starry Night image?

Ok, I found the star (Starry night) also last night it was clear enough.

Are the directions still the same for those down North that cannot see The southern cross (but as you used mostly accurate terminology, should have been named Crux)

I'd love to try that here, but being under Stage 3 (something) water restrictions, I think one of my neighbors will call the police ;o(

Not for much longer Mate. Which ever end of that road. You will have time to waste water, and time, all at the same time. That's three for the price of one! Remember the rainbows we could create in the yard when using a hose?

Ever seen a cat run towards a sprinkler? I'd see light escaping the black hole first. A bit agro today Ky?

It's getting on dark here so the plants are next. Photo synthesis was the other thing that only works in the here and now. So Stevie Wonder comes to mind. "The secret life of plants". Go and listen. Acquire the taste if you have not heard it. Light travels and he wonders about nothing and is in the hear/here and now.

It's a hard rain gonna fall. Ky.

Boring - except for the part about Del runing toward a sprinkler.

I am trying to be more human and more logical at the same time. Ky.

The smart ass answer would be, Sure, light is stored in flourescent tube that is released when excited electrically. The ends turn dark when it's empty. You'd be surprised how many people fall for that. Or, my personal favorite, an incandescent light bulb emits light, while a flourescent tube actually absorbs darkness. It's a "dark absorber". When it's full, the ends turn dark, and it won't work anymore. Even more people fall for that one.

Ah, what the mind turns to, trying to while away the months at sea!

Beautiful indel!

This on a engineering site? What will they think of next. Who was the Author? Or is it just your middle of the road Texan wisdom? Light will never be the same to me after all of this. Thank you. Ky.

Thank you for your kind words. The translation (I wish it was mine!) is not the best, but shows some depth of thinking.

Romanian poet Eminescu wrote it in December 1886.

You know what, I will put music to it and send it to you when done. This is, if CR4 would except sound files. Maybe they do and I haven't found the way to do such an operation yet.

Some one will tell me if it can be done, I'm sure. These people at CR4 are so helpful, which includes us.

Pearls for the swines? I don't think so! I shouldn't even be talking to a 'Guest" like that. But then again, at the light of day, nobody really cares unless involved in a subject.

Greetings. Ky.

PS:

Your Bridge rules should continue "unless the opponent is Chinese". Never one a game!

You know what, I will put music to it and send it to you when done.

Do that, and I will send it to the Romanian TV. Could be your place to launch your artistic carrier

See what happens. What ever will be will be. I would like some gymnasts to be choreographed if that is possible. Playing with the lightness of light past, present or future should be very rewarding. Ky.