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Universe's Dark Ages May Not Be Invisible After All
StartsWithABang writes: The Universe had two periods where light was abundant, separated by the cosmic dark ages. The first came at the moment of the hot Big Bang, as the Universe was flooded with (among the matter, antimatter and everything else imaginable) a sea of high-energy photons, including a large amount of visible light. As the Universe expanded and cooled, eventually the cosmic microwave background was emitted, leaving behind the barely visible, cooling photons. It took between 50 and 100 million years for the first stars to turn on, so in between these two epochs of the Universe being flooded with light, we had the dark ages. Yet the dark ages may not be totally invisible, as the forbidden spin-flip-transition of hydrogen may illuminate this time period after all.
is not scientific news, nor does the link point to any academic results. "Ask Ethan" is simply a popular-scientific discussion of results already known. So no News for Nerds, and hardly any Stuff that Matters, IMHO.
Religous speak to God. Insane are spoken to by God. When all shut up, one can finally hear Shostakovich in peace
No. We looked at the sun. Helium is something we can see, though, not with our eyes.
You see, beyond the basic blackbody radiation (Which is purely due to matter radiating heat), each atom glows at specific wavelengths - this happens when an electron moves to a lower energy state (Think: smaller orbit), and emits a photon at the energy level that corresponds to the difference. Every atom has its own set of wavelengths that it emits - this is called the emission spectrum, and if you stretch out the spectrum of a point of light, you can see bright spots that correspond to this emission spectrum.
Additionally, each atom has a set of wavelengths that it highly efficient at absorbing. These appear as darker spots when you spread out the spectrum of a star. These are called absorption spectrum, and they are unique to each element.
Analyzing the emission and absorption spectrum of the Sun showed that it was largely made up of a gas that hadn't been discovered, because there were strong emission and absorption lines that corresponded to an element we hadn't yet discovered. This gas was named "Helium", after the Greek word "Helios", meaning the sun.
A number of years later, knowing that there was strong evidence of its existence, chemists managed to isolate Helium in the lab, and ran tests on it to measure the properties of Helium's spectrum, and it matched to what we saw in the Sun.
This is how we know the Sun is made of Helium.
The energy is expressed as wavelength - higher energy photons have shorter wavelengths.
And, if it helps, shorter wavelengths = higher frequency, if you choose to describe it that way (Since, the frequency in Hz of light, including radio, is the distance light travels in a second divided by the wavelength).
Blue light is higher energy than red light.
X-Rays are higher energy than any visible light.
Radio waves are lower energy than any visible light.
Gamma rays are higher energy than X-Rays (and all other photons, because past a point, we call everything a gamma ray)
http://en.wikipedia.org/wiki/E...
If you had enough energy to make one 350nm photon (a wavelength that just might be visible, maybe, as it is UV), you could instead make two 700nm photons with the same energy (which also might just barely be visible, as it is at the edge of infrared). More reasonably, if you had enough energy to make 3 blue photons, you could instead make 4 red ones with that same amount of energy.
http://en.wikipedia.org/wiki/V...
http://www.chemteam.info/Elect...