Top Document: [sci.astro] Astrophysics (Astronomy Frequently Asked Questions) (4/9) Previous Document: D.11 What are magnetic monopoles? Are they real? Next Document: D.13 Saturn's rings, proto-planetary disks, accretion disks---Why are disks so common? See reader questions & answers on this topic! - Help others by sharing your knowledge Empty space itself cannot have a temperature, unless you mean some abstruse question about quantum vacuums. However, if you put a physical object into space, it will reach a temperature that depends on how efficiently it absorbs and emits radiation and on what heating sources are nearby. For example, an object that both absorbs and emits perfectly, put at the Earth's distance from the Sun, will reach a temperature of about 280 K or 7 C. If it is shielded from the Sun but exposed to interplanetary and interstellar radiation, it reaches about 5 K. If it were far from all stars and galaxies, it would come into equilibrium with the microwave background at about 2.7 K. Spacecraft (and spacewalking astronauts) often run a bit hotter than 280 K because they generate internal energy. Arranging for them to run at the desired temperature is an important aspect of design. Some people also consider the "temperature" of high energy particles like the solar wind or cosmic rays or the outer parts of the Earth's atmosphere. These particles are not in thermal equilibrium, so it's not correct to speak of a single temperature for them, but their energies correspond to temperatures of thousands of kelvins or higher. Generally speaking, these particles are too tenuous to affect the temperature of macroscopic objects. There simply aren't enough particles around to transfer much energy. (It's the same on the ground. There are cosmic rays going through your body all the time, but there aren't enough to keep you warm if the air is cold. The air at the Earth's surface is dense enough to transfer plenty of heat to or from your body.) User Contributions:Top Document: [sci.astro] Astrophysics (Astronomy Frequently Asked Questions) (4/9) Previous Document: D.11 What are magnetic monopoles? Are they real? Next Document: D.13 Saturn's rings, proto-planetary disks, accretion disks---Why are disks so common? 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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