Interesting facts

[Quasar]

This thread is for interesting facts about the Universe...

Algoran gave us this:-

Hello all! Astronomy is most certainly very cool. Im a fan of all things space-related - astronomy, scifi... X3

Here is a random piece of information people may or may not be interested in. Feel free to ignore me if not:

There are no green stars. Why? It was quite awhile after first asking this question that i found what seems a reasonable answer. The human eye has a dip in perception around green, or more correctly it has two peaks, at yellow and blue.

Stars glow simply because they are hot, and like all objects that do as much they emit light across the entire electromagnetic spectrum, with a peak at a point determined by their temperature.

This peak is not terribly high - no star has a very strong colour. As it happens in the case of green stars ('medium' temperature) the peak is more or less canceled out by the dip in the human eye's perception, so the star appears white.

[J VORTEX]

interesting, more please.

[Quasar]

most of us have heard of Neutron Stars, or Pulsars (so called because they emit a pulse at radio wavelengths), which have their atoms so squashed together that the protons are turned into neutrons by joining with electrons and the neutrons are squashed tightly together...

most of us have also heard of a Black Hole where the gravity is so great that not even light can escape...

well... there is a small varient in between the two, called a Quark Star and it is very rare, it is thought that 2 have now been positively identified... the gravity is too high for even neutrons to survive, and it crushes the neutrons causing them to breakdown into a quark soup (hence Quark Star).

Why is it so rare?
Because a little lighter and it'd be a Neutron Star, and a little heavier and it'd be a Black Hole.

[Quasar]

a few more facts:-

A star begins as a cloud of dust and gas, which condenses to form a single star, a two-star system also known as a binary star, or a star cluster which may contain several.

The first telescope was built in the early 1600s, by Dutch lens-grinder Hans Lipperhey.

The first asteroid to be discovered was Ceres, in 1801. It is believed there are millions of asteroids in our solar system, but only about 264,000 have been identified, and only about 12,136 of those have been named.

A comet looks like a dirty snowball until it approaches the Sun--a comet’s nucleus only shines when reflecting the Sun’s light, and the comet’s head and tail don’t form until the Sun’s heat causes dust and gas to evaporate.

According to some estimates, approximately 19,000 meteorites weighing about 3.5 ounces each shower the Earth every day, but only about 10 are recovered each year.

The first solar flares were recorded on Sept. 1, 1859, by scientists Richard C. Carrington and Richard Hodgson.

The Sun is the largest object in the solar system, and constitutes over 99 percent of the solar system’s mass.

A star’s color depends on its temperature: blue stars have the highest temperatures, followed by yellow-white stars, and finally by red stars, which have the coolest temperatures.

[Cebraio]

I don't know much about astronomy but I know some facts about the human eye. So regarding Algorans post: The human eye has no "dip" at green. Humans are actually capable to distinguish most colors from the green spectrum. The "dip", if you want to call it like that, is moreover in the blue perception. See also this wiki article (http://en.wikipedia.org/wiki/Color_vision) and the picture showing the spectrum of responses by human cone cells. The blue cone cells show less response than red and green.

Now to tread on creationists toes: The reason for the better vision of green colors is presumably our evolution in woods and hunting for food. How much blue prey do you know? And how much blue is there anyway - despite water and blueberries? So, no need to distinguish many blue tones.

Why there are no green stars? I don't know. Maybe they just don't burn in green sprectrum. Maybe this is a good point to start reading: http://en.wikipedia.org/wiki/Star#Classification

[Algoran]

a few more facts:-

A star begins as a cloud of dust and gas, which condenses to form a single star, a two-star system also known as a binary star, or a star cluster which may contain several.

The largest number of stars known to be in a single system is 6, for example the 'star' Castor.

And I forget the exact proportions, but I think over half of all stars/star systems are binaries, with trinaries and single stars being less common.

I don't know much about astronomy but I know somefacts about the human eye. So regarding Algorans post: The human eye has no "dip" at green. Humans are actually capable to distinguish most colors from the green spectrum. The "dip", if you want to call it like that, is moreover in the blue perception. See also this wiki article (http://en.wikipedia.org/wiki/Color_vision) and the picture showing the spectrum of responses by human cone cells. The blue cone cells show less response than red and green.

Now to tread on creationists toes: The reason for the better vision of green colors is presumably our evolution in woods and hunting for food. How much blue prey do you know? And how much blue is there anyway - despite water and blueberries? So, no need to distinguish many blue tones.

Why there are no green stars? I don't know. Maybe they just don't burn in green spectrum. Maybe this is a good point to start reading: http://en.wikipedia.org/wiki/Star#Classification

Well from looking at that response spectrum, I would say the dip is in green - although offcenter towards blue. Its around 480nm, and compared with the electromagnetic spectrum here: http://en.wikipedia.org/wiki/Electromagnetic_spectrum
Green is around 500nm.

Also there certainly should be green stars, because as Quasar said a stars colour depends on its temperature - this is because stars act as blackbodies, meaning they glow simply because they are hot, and emit a spectrum of a predictable shape with a peak output at a wavelength defined by their temperature. The hotter they are, the shorter the wavelength at the peak: http://en.wikipedia.org/wiki/Blackbody

If you still wanted to do some creationist toe-treading you could observe we have a high sensitivity in the yellow region of the spectrum, where the sun outputs most strongly :)

[Aragon Speed]

It should also be noted that the human eye has more green receptors than any other colour, and psychologically green is the only colour the mind does not get bored of and finds the most relaxing. (As long as it's a natural green (and not neon lighting for example) of course. :grin:) And yes this does relate to our evolution. ;)

[Cebraio]

Also there certainly should be green stars, because as Quasar said a stars colour depends on its temperature - this is because stars act as blackbodies, meaning they glow simply because they are hot, and emit a spectrum of a predictable shape with a peak output at a wavelength defined by their temperature. The hotter they are, the shorter the wavelength at the peak: http://en.wikipedia.org/wiki/Blackbody
Thanx for the blackbody link. I forgot about that and there you find an interesting image (http://en.wikipedia.org/wiki/Image:PlanckianLocus.png). Doesn't it explain why there are (almost ?) no green stars? The graph doesn't really go into the green part of the spectrum and around 6000°K it looks probably more white than green.

Also from looking at the response spectrum (http://en.wikipedia.org/wiki/Image:Cones_SMJ2_E.svg) I would say the dip is around 485nm. If we can believe that Planckian Locus image (in contrary to the electromagnetic spectrum image), then it looks like at 485nm there is pretty much blue, followed by turquoise.

[Algoran]

Hmm you're right, it dosnt seem to go far into the green.. But im not sure what those perpendicular lines are supposed to indicate?

But, if we had reduced perception to blue, isnt it odd we can see blue stars..?

Or maybe im just not as clever as i think i am :p

Regardless, I cant think why you wouldnt get stars that peak in the green.

[Cebraio]

It just came into my mind to ask the great oracle about green stars and look what it showed me:
http://www.astronomycafe.net/qadir/q72.html

I think the most important part that we missed so far, is this:
Another factor working against us is that we see stars in the sky using our black/white rods not our color-sensitive cones. This means that only the very brightest stars have much of a color, usually red, orange, yellow and blue. By chance there are no stars nearby that would have produced green colors had their spectral shapee been just right.

That site probably has more interesting information for you guys, if you look into the index.

[Quasar]

The earth's end may not be as often predicted... that the sun will expand and swallow the earth in approximately 5 billion years, before becoming a white dwarf...

Why? Because in approximately 4.5 billion years, our galaxy, the Milky Way, is due to begin a collision with the Andromeda Galaxy... exactly what will happen, and what will become of the solar system, is not known at this point... however, the radiation from the two supermassive black holes becoming active is likely to extinguish all life in both galaxies... and some stars will likely be cast out into the intergalactic void...

While the media and others use "light years" to determine distance in the universe, Astronomers do not... the "parsec" is the unit they use, and it is defined as the distance from our Sun to Alpha Centauri, the nearest star to us (approximately 4.6 light years)...

[Aragon Speed]

Astronomers do not...
Of course they don't. Why on earth would they want to use a unit that everyone can easily understand (Light years) instead of an arbitrary one (parsecs) that makes working out how far away something is harder for the normal mind to grasp. :rolleyes:8)

[Quasar]

the distances are so vast, it doesn't really matter, as the mind can't really appreciate the difference between a distance like a million parsecs or 4.5 million light years... it's just one hellva long way!! :grin:

[Snowship]

I dunno though; Being in the solar system of one of the suns flung into deep space might be interesting (at least the stars in the sky would change)

[Quasar]

:lol: you'd have a galactic lens view, that was very large, and very slowly shrinking... a bit like a couple of sectors in the New Horizon's Mod, very spectacular! :grin: