The Venus Transit 2004
... Brief InfoSheet G1
What is LIGHT?
All cosmic bodies emit radiation - photons. Gamma photons come from a violent universe. A hot Universe is observed in X-rays. Infrared radiation is emitted by a warm universe (in near infrared) and cold universe in far infrared. Some photons reaching our eyes are less than one thousandth of a second old (lightning, meteors), others are milions of years. In microwaves astronomers observe the oldest light of all, from the time when Universe was 300 000 years old. At that time the Universe became transparent. Since then the Universe (and the wavelengths of radiation) expanded 10 000 times and during the 13 billions years the light has changed into microwave radiation. It is called the cosmic background radiation. In the Cosmos, there are two billion (2 x 10 9 ) relic photons for each protons. They are by far the most abundant photons in the Universe.
This topic is discussed in a more detailed way in the associated Extended InfoSheet.
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