Astronomy-Interesting Facts

[PeiWen]

Four small planets lie quite close to the Sun. All of them have about the same density as the Earth and so they are called "Terrestrial". Besides the Earth, they are Mercury, Venus, and Mars. The most distant of these planets from the Sun is Mars, a little over 1.5 A.U. from the Sun. Want to walk about 350 million miles? Then head for the next nearest planet: Jupiter.
As you cross the road on your way to Jupiter, watch out for vehicle traffic! If you were crossing between the orbits of Mars and Jupiter in the actual Solar System, you would have to watch out for asteroids. They are found in great numbers in this region of the Solar System (they appear on the Solar System Map of the Inner Planets as Ida and Gaspra) near the giant planet Jupiter. It's the largest planet in our Solar System and its strong gravitational tug probably broke up a small planet that came too close.

As you walk along the path from the model of Neptune to the model of Pluto, you are following the orbital path of Neptune as it circles the Sun - but in the opposite direction to the real motion of the planet. It would take Neptune about 20.5 years to make the trip you will complete in about 3.5 minutes!

Pluto is about 1600 feet, in a direct line, from the corner of Albertus Hall - where our solar walk began. The real Pluto is nearly 4 billion miles from the Sun! Our walk from the Sun to Pluto took about 15 minutes: light from the Sun, traveling at 186,000 miles per second, would take about 5.5 hours to reach Pluto.

[PeiWen]

Four small planets lie quite close to the Sun. All of them have about the same density as the Earth and so they are called "Terrestrial". Besides the Earth, they are Mercury, Venus, and Mars. The most distant of these planets from the Sun is Mars, a little over 1.5 A.U. from the Sun. Want to walk about 350 million miles? Then head for the next nearest planet: Jupiter.
As you cross the road on your way to Jupiter, watch out for vehicle traffic! If you were crossing between the orbits of Mars and Jupiter in the actual Solar System, you would have to watch out for asteroids. They are found in great numbers in this region of the Solar System (they appear on the Solar System Map of the Inner Planets as Ida and Gaspra) near the giant planet Jupiter. It's the largest planet in our Solar System and its strong gravitational tug probably broke up a small planet that came too close.

As you walk along the path from the model of Neptune to the model of Pluto, you are following the orbital path of Neptune as it circles the Sun - but in the opposite direction to the real motion of the planet. It would take Neptune about 20.5 years to make the trip you will complete in about 3.5 minutes!

Pluto is about 1600 feet, in a direct line, from the corner of Albertus Hall - where our solar walk began. The real Pluto is nearly 4 billion miles from the Sun! Our walk from the Sun to Pluto took about 15 minutes: light from the Sun, traveling at 186,000 miles per second, would take about 5.5 hours to reach Pluto.

[PeiWen]

Please try out this link, it's a simulator that can show you whichever planet you wish to view from whichever location...have fun!

http://space.jpl.nasa.gov/

[PeiWen]

Please try out this link, it's a simulator that can show you whichever planet you wish to view from whichever location...have fun!

http://space.jpl.nasa.gov/

[jo_n]

say. what's the difference between astrology and astronomy? just asking? :wink:

[__earth]

Astronomy is the study of celestial bodies. It is science. Astronomy has nothing to do with astrology.

Astrology is about predicting one's fortune. Astrology is a pseudoscience and pretends to use astronomy in its practice.

It is simply an unfortunate decision to have astrology and astronomy in one sig.

[Zeroth]

Astrology is metascience, Astronomy is science, haha!

Similarity is, they both involve the stars.. haha!

[tezuka87]

If the sun blots out it would take 8 minutes for us to find out..this is cos it takes 8 minutes for the sun's light to reach earth. This also means that the sun we see is actually the sun as it was 8 minutes ago.

Similarly, the moon we see is the moon as it was 1 minute ago.

[youngyew]

If the sun blots out it would take 8 minutes for us to find out..this is cos it takes 8 minutes for the sun's light to reach earth. This also means that the sun we see is actually the sun as it was 8 minutes ago.

Similarly, the moon we see is the moon as it was 1 minute ago.
The light from moon should be about 1.2 to 1.3 seconds ago, as the moon's distance from earth is 360,000 km to 400,000 km while the speed of light is about 300,000 km/s.

Anyway, it's interesting to think about the speed of light in terms of interstellar distances. There's an interesting paragraph in Bill Bryson's book "A Short History of Nearly Everything" about Drake equation:

"... Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least two hundred light years, which is a great deal more than merely saying it makes it sound. It means, for a start, that even if these beings know we are here and are somehow able to see us in their telescopes, they're watching light that left Earth two hundred years ago. So they're not seeing you and me. They're watching the French Revolution and Thomas Jefferson and people in silk stockings and powdered wigs - people who don't know what an atom is, or a gene, and who make their electricity by rubbing a rod of amber with a piece of fur and think that's quite a trick. Any message we receive from these observers is likely to begin 'Dear Sire', and congratulate us on the handsomeness of our horses and our mastery of whale oil. Two hundred light years is a distance so far beyond us as to be, well, just beyond us."

[tezuka87]

The light from moon should be about 1.2 to 1.3 seconds ago, as the moon's distance from earth is 360,000 km to 400,000 km while the speed of light is about 300,000 km/s.


I stand corrected! :) Yeah...should do calculations b4 claiming something. :oops:

Hey, true! If it's possible to see such things...hehehehe...nothing is secret anymore! You can murder someone, and then it is possible to find out!!! Brings a whole new meaning to the Chinese idiom "tian wang hui hui, shu er bu lou". I think its "The wheels of God grind slowly, but they grind exceeding small." in English...Criminals, beware! I (Mr Alien) know wat you did last summer...kakakka

[vseehua]

I stand corrected! :) Yeah...should do calculations b4 claiming something. :oops:I stand corrected means you hold that your previous claims are correct, but you seemed to admit your mistake in the phrase afterwards. So which one is correct?

[tezuka87]

I'm WRONG. The moon we see is the moon as it was 1.2~1.3 seconds ago.

I was just under the wrong impression that 'I stand corrected' means 'Yes, I have been corrected. I bow my head, I admit defeat.'

Or am I really under the wrong impression? If I wanted to say I am actually correct, wouldn't I say 'I am actually correct' :roll: rather than use the term 'corrected'?

Thank you, dear vseehua....please correct me if I am wrong. :roll:

Anyway, another related interesting astronomical fact...There are many stars in the sky which we can see but which really don't exist anymore...[/b]

[vseehua]

I'm WRONG. The moon we see is the moon as it was 1.2~1.3 seconds ago.

I was just under the wrong impression that 'I stand corrected' means 'Yes, I have been corrected. I bow my head, I admit defeat.'

Or am I really under the wrong impression? If I wanted to say I am actually correct, wouldn't I say 'I am actually correct' :roll: rather than use the term 'corrected'?

Thank you, dear vseehua....please correct me if I am wrong. :roll:

Anyway, another related interesting astronomical fact...There are many stars in the sky which we can see but which really don't exist anymore...[/b]As far as i know, the term "i stand corrected" literally means my points are corrected and i refuse go budge from it. That is what i can derive from the numerous time that i had encountered this phrase...

The fact is based on the fact that the light from the stars required time to travel to our eyes. In fact, the time that it takes to travel to our eyes are so long that they are can take millions if not billions of years to do so. Since the speed of light is determined to be about 300,000 m/s you can imagine that the size of the universe if indeed very epic in itself.

The light from the stars that you are looking now actually have been emitted in the past, as such, you are looking at the history of the star, not the present state of it ;)

[KenChan]

If the sun blots out it would take 8 minutes for us to find out..this is cos it takes 8 minutes for the sun's light to reach earth. This also means that the sun we see is actually the sun as it was 8 minutes ago.

Similarly, the moon we see is the moon as it was 1 minute ago.
The light from moon should be about 1.2 to 1.3 seconds ago, as the moon's distance from earth is 360,000 km to 400,000 km while the speed of light is about 300,000 km/s.

Anyway, it's interesting to think about the speed of light in terms of interstellar distances. There's an interesting paragraph in Bill Bryson's book "A Short History of Nearly Everything" about Drake equation:

"... Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least two hundred light years, which is a great deal more than merely saying it makes it sound. It means, for a start, that even if these beings know we are here and are somehow able to see us in their telescopes, they're watching light that left Earth two hundred years ago. So they're not seeing you and me. They're watching the French Revolution and Thomas Jefferson and people in silk stockings and powdered wigs - people who don't know what an atom is, or a gene, and who make their electricity by rubbing a rod of amber with a piece of fur and think that's quite a trick. Any message we receive from these observers is likely to begin 'Dear Sire', and congratulate us on the handsomeness of our horses and our mastery of whale oil. Two hundred light years is a distance so far beyond us as to be, well, just beyond us."

its possible for an object to travel faster than the speed of light.
care to give me your opinion?

[Zeroth]

I thought it's impossible to travel beyond the speed of light?

[youngyew]

In Einstein's frameworks, nothing can travel faster than light. However, nobody really says that nothing exists outside Einstein's framework, so who knows, one day it might be possible?

But of course I am not qualified to talk about this thing, just some random ramblings here.

[Al-Bert]

Did you all ever heard of Cerenkov Radiation? I don't really understand its meaning...but i guess it has something to do with the phenomenon when a particle travel faster than the speed of light....means it should be possible for an object to travel faster than light!

Wanna ask something, light beam has the speed of 300000 km/s....
Do you think the speed of light beam will increase when we shoot the light beam in a constant velocity moving vehicle?

Let say if the velocity of the vehicle is 200km/s....will the speed of light beam shot from the vehicle increase to 300200 km/s ?

[youngyew]

Did you all ever heard of Cerenkov Radiation? I don't really understand its meaning...but i guess it has something to do with the phenomenon when a particle travel faster than the speed of light....means it should be possible for an object to travel faster than light!

Wanna ask something, light beam has the speed of 300000 km/s....
Do you think the speed of light beam will increase when we shoot the light beam in a constant velocity moving vehicle?

Let say if the velocity of the vehicle is 200km/s....will the speed of light beam shot from the vehicle increase to 300200 km/s ?
I can't comment much about the cerenkov radiation.

For your question about the light beam, no, regardless of the velocity of the vehicle, the velocity measured from the car is still c, 299,792.458 km/s. This counter-intuitive result holds true in our observable universe, and it in fact forms the basis of the theory of special relativity by Einstein. Read more here:

http://en.wikipedia.org/wiki/Speed_of_light

[tezuka87]

Harlo, feel like reviving this thread...a bit... :D

Cerenkov radiation is the electromagnetic radiation emitted when a (charged) particle travels faster in a medium than the speed of light in the same medium...

I guess when people say nothing can travel faster than the speed of light, they mean the speed of light in a VACUUM...

[Al-Bert]

I could comprehend why Sun could "burn" without oxygen gas...

However, I have no idea why something would get burned when it travels close to the Sun? ( There's no any kind of gas particle exist in outerspace )

[youngyew]

In the absence of oxidant (e.g. oxygen), you will most probably melt / denature instead of burn when you are heated up.

[vseehua]

In Einstein's frameworks, nothing can travel faster than light. However, nobody really says that nothing exists outside Einstein's framework, so who knows, one day it might be possible?

But of course I am not qualified to talk about this thing, just some random ramblings here.In Einstein's frameworks, there is nothing that prevents anything from travelling faster from light. It just states that we cannot ever accelerate from 0 to the speed of light. However, it doesn't state that an particle cannot travel natively faster than light.

I could comprehend why Sun could "burn" without oxygen gas...

However, I have no idea why something would get burned when it travels close to the Sun? ( There's no any kind of gas particle exist in outerspace )That is burning in the sense of combustion. In the case of something burned while being close to the sun, it is refering to the melting-evaporating-plasmafication of matter/destruction of chemical bonds when it gets too heated because of the heat radiating from the sun's surface...



Wanna ask something, light beam has the speed of 300000 km/s....
Do you think the speed of light beam will increase when we shoot the light beam in a constant velocity moving vehicle?

Let say if the velocity of the vehicle is 200km/s....will the speed of light beam shot from the vehicle increase to 300200 km/s ?
When you move, your time actually slows in relative to your surroundings, which makes it possible for light to stay at a constant speed however fast that you are moving.

It had been tested in the 70s by putting an atomic clock on a concorde and one on the surface of the Earth. The one on the concorde is a tiny bit slower than the one which is on the surface of the Earth but still measurable to an extent.

Strange as it sounds, but that is some of the most accurate predictions that General Relativity had predicted to date...

[bluez_aspic]

In Einstein's frameworks, there is nothing that prevents anything from travelling faster from light. It just states that we cannot ever accelerate from 0 to the speed of light. However, it doesn't state that an particle cannot travel natively faster than light.
There are such hypothetical particles known as tachyons, but even if they were to exist information would still not be transmitted faster than the speed of light. General relativity reduces to special relativity in a local sense, but I've routinely read articles (usually re: big bang) which claims that the equations permit space to expand in such a way that two objects, located at a great distance apart, can have a recession velocity greater than the speed of light. Note that this refers to an expansion of space, not motion through space - so Special Relativity is not violated.

(to see this space expansion thing - assume that the universe expands in such a way that its size is doubled every 1 year. So two planets A and B which were initially, say, 5 light years apart, would now be 10 light years apart. But this took place in the time span of only 1 year. So from the perspective of A, planet B would have receded much faster than the speed of light)

Most 'faster-than-light' phenomena involves 'cheating' in some sense - but information still is not transmitted faster than light. If that were to be the case, cause-and-effect would be literally turned upside down - one immediate consequence would be that the laws of physics would appear different to different observers. Terrible indeed, but so far we have no reason to conclude otherwise.

When you move, your time actually slows in relative to your surroundings, which makes it possible for light to stay at a constant speed however fast that you are moving.
This isn't quite accurate, actually. One of the fundamental postulates of Special Relativity is the universality of the speed of light - that whatever you do, whether you were to travel fast or slow or remain motionless, light will always travel at the same speed. It's taken as an AXIOM, a FUNDAMENTAL TRUTH - and so far that has been well corroborated by experimental evidence.

It's weird and mysterious, isn't it? A good way to understand this is to try comparing the speed of light (which is independent of both source and receiver), to the apparent speed of a ball (which depends on both the speed of the source and receiver), and the way in which sound travels (independent of the speed of the source, but dependent on the speed of the receiver relative to the medium).


re: Al-Bert - If you're serious about picking up Special Relativity, it's actually quite easy (only requires knowledge of Pythagoras' theorem and elementary algebra) - Halliday, Resnick and Walker has a chapter or two dedicated to a gentle introduction on the subject. Special Relativity by A.P. French. is more hardcore, but that happens to be my favourite text.

[vseehua]

This isn't quite accurate, actually. One of the fundamental postulates of Special Relativity is the universality of the speed of light - that whatever you do, whether you were to travel fast or slow or remain motionless, light will always travel at the same speed. It's taken as an AXIOM, a FUNDAMENTAL TRUTH - and so far that has been well corroborated by experimental evidence.

It's weird and mysterious, isn't it? A good way to understand this is to try comparing the speed of light (which is independent of both source and receiver), to the apparent speed of a ball (which depends on both the speed of the source and receiver), and the way in which sound travels (independent of the speed of the source, but dependent on the speed of the receiver relative to the medium).


re: Al-Bert - If you're serious about picking up Special Relativity, it's actually quite easy (only requires knowledge of Pythagoras' theorem and elementary algebra) - Halliday, Resnick and Walker has a chapter or two dedicated to a gentle introduction on the subject. Special Relativity by A.P. French. is more hardcore, but that happens to be my favourite text.
Well, i am trying to put it in a way that more people can understand what is going on :P Something like the electronic shells in the atoms taught during our SPM years:laugh

[Al-Bert]

Is black hole a kind of wormhole?

And if no light could escape from black hole ( means we can't see black hole ), then how come Hawking radiation from the black hole could be observed?

[bluez_aspic]

Is black hole a kind of wormhole?

And if no light could escape from black hole ( means we can't see black hole ), then how come Hawking radiation from the black hole could be observed?
My memory is rather fuzzy on this one, but I'll give it a shot:

A wormhole is two separate black holes being connected by a 'tunnel' (in the fabric of space-time) - but it's more of a sci-fi concept, really. The existence of black holes on the other hand rests on a sounder basis, since the equations of General Relativity predicts their existence - whether they truly exist is another thing altogether. I'm not quite sure what the consensus is nowadays.

Hawking radiation is emitted from a black hole due to a quantum mechanical effects (the Heisenberg uncertainty principle, to be precise). Primordial black holes (i.e. those which were formed in the infancy of the universe) could emit more Hawking radiation than they suck in, and thus this would enable primordial black holes to be observed. But it's said that the emitted radiation would be very weak, so not much success in verifying this one either.

[vseehua]

Observations have proved that black holes do exist in the universe... so far, because of the limits of certain extreme conditions like a glaxy being able to hold it's mass or matter (stars, materials) together.

A wormhole, however, is a hypothesis that have not yet been proved, or calculated to a convincing extent. This will be the reason why i would call it hypothesis. Wiki article here (http://en.wikipedia.org/wiki/Wormhole).

More about Hawking Radiation here. (http://en.wikipedia.org/wiki/Hawking_radiation)Notice that the radiation doesn't really come from inside the hole, rather, just above the event horizon. So the statement about things needing to travel more than the speed of light to excape a black hole still holds.

[Al-Bert]

I understand that the formula to calculate the wave energy is E=hf, where E is energy, h is Planck contant and f is frequency of wave.

My doubt : wouldn't the amplitude of the wave bring any effect to wave energy? I mean, you need work in order to increase the intensity of a wave, thus don't you think that the work done will be converted into the new energy of the wave? But the formula E=hf doesn't seem to endorse it.

[youngyew]

The E=hf formula is for the energy of a single photon. Amplitude of a wave reflects the number of photons, but it doesn't affect the energy contained in each photon.

[ChristopherCWL]

Anything to do with the E=MC^2 formulae??