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Top Document: [sci.astro] Cosmology (Astronomy Frequently Asked Questions) (9/9) Previous Document: I.14. Can the CMB be redshifted starlight? Next Document: I.16. What about objects with discordant redshifts? See reader questions & answers on this topic! - Help others by sharing your knowledge If the Universe were infinitely old, infinite in extent, and filled with stars, then every direction you looked would eventually end on the surface of a star, and the whole sky would be as bright as the surface of the Sun. This is known as Olbers' Paradox after Heinrich Wilhelm Olbers (1757--1840) who wrote about it in 1823--1826 (though it had been discussed earlier). A common suggestion for resolving the paradox is to consider interstellar dust, which blocks light by absorping it. However, absorption by interstellar dust does not circumvent this paradox, as dust reradiates whatever radiation it absorbs within a few minutes, which is much less than the age of the Universe. The resolution of Olbers' paradox comes by recognizing that the Universe is not infinitely old and it is expanding. The latter effect reduces the accumulated energy radiated by distant stars. Either one of these effects acting alone would solve Olbers' Paradox, but they both act at once. User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] Cosmology (Astronomy Frequently Asked Questions) (9/9) Previous Document: I.14. Can the CMB be redshifted starlight? Next Document: I.16. What about objects with discordant redshifts? Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
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[sci.astro] Cosmology (Astronomy Frequently Asked Questions) (9/9)
Section - I.15. Why is the sky dark at night? (Olbers' paradox)
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[sci.astro] Cosmology (Astronomy Frequently Asked Questions) (9/9)
Section - I.15. Why is the sky dark at night? (Olbers' paradox)
( Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page
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with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP