72 captures

08 Apr 2000 - 28 Mar 2022

Dec	JUN	Sep
	26
2014	2016	2017

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About this capture

COLLECTED BY

Organization: Internet Archive

The Internet Archive discovers and captures web pages through many different web crawls. At any given time several distinct crawls are running, some for months, and some every day or longer. View the web archive through the Wayback Machine.

Collection: Wide Crawl Number 14 - Started Mar 4th, 2016 - Ended Sep 15th, 2016

The seed for Wide00014 was:

- Slash pages from every domain on the web:

-- a list of domains using Survey crawl seeds

-- a list of domains using Wide00012 web graph

-- a list of domains using Wide00013 web graph

- Top ranked pages (up to a max of 100) from every linked-to domain using the Wide00012 inter-domain navigational link graph

-- a ranking of all URLs that have more than one incoming inter-domain link (rank was determined by number of incoming links using Wide00012 inter domain links)

-- up to a maximum of 100 most highly ranked URLs per domain 

The seed list contains a total of 431,055,452 URLs
The seed list was further filtered to exclude known porn, and link farm, domains
The modified seed list contains a total of 428M URLs

TIMESTAMPS

NEW TECHNOLOGY

During the past few decades, infrared astronomy has become a major field of science due to the rapid advances in infrared detector technology. Many of these advances arose from U.S Department of Defense research into infrared array technology in the 1980's. Infrared radiation, having longer wavelengths and lower energy than visible light, does not have enough energy to interact with the photographic plates which are used in visible light astronomy. Instead infrared astronomers rely on electronic devices to detect radiation. Early infrared astronomers used thermocouples and thermopiles (a group of thermocouples combined in one cell).

In the 1950's astronomers started to use Lead-sulphide (PbS) detectors to study infrared radiation in the 1 to 4 micron range. When infrared radiation in this range falls on a PbS cell it changes the resistance of the cell. This change in resistance can be measured and is related to the amount of infrared radiation which falls upon the cell. To increase the sensitivity of the PbS cell it was cooled to a temperature of 77 degrees Kelvin by placing it in a flask filled with liquid nitrogen.

A major breakthrough came in 1961, with the development of the germanium bolometer. This instrument was hundreds of times more sensitive than previous detectors and was capable of detecting all infrared wavelengths. Basically, a cool thin strip of germanium is placed in a container which has a small opening in it. When infrared radiation comes through the opening and hits the germanium, it warms the metal and changes its conductivity (a measure of how much electrical current flows through an object). The change in conductivity can be measured and is directly proportional to the amount of infrared radiation entering the container. The germanium bolometer works best at an extremely low temperature (much lower than liquid nitrogen). The best way to cool the bolometer to such a low temperature is to surround it with liquid helium which cooled it to 4 degrees Kelvin. This is only a few degrees above absolute zero. To do this a metal Dewar (similar to a well insulated thermos flask) was developed which was able to hold the liquid helium in which the germanium bolometer was immersed. This type of infrared detector is sensitive to the entire range of infrared wavelengths. To study a particular wavelength of infrared emission from astronomical objects, astronomers place filters in front of the detectors, which filter out all but the desired wavelengths.

Infrared detector technology continues to advance at a rapid rate. Astronomers now use InSb and HgCdTe detectors for the 1 to 5 micron range. These operate in a way similar to the PbS detectors but use materials which are much more sensitive to the infrared. The development of infrared array detectors in the 1980's caused another giant leap in the sensitivity of infrared observations. Basically a detector array is a combination of several single detectors. These arrays allow astronomers to produce images containing tens of thousands of pixels at the same time. Infrared arrays have been used on several infrared satellite missions. In 1983 the IRAS mission used an array of 62 detectors. Astronomers now commonly use 256x256 arrays (thats 65,536 detectors!). Due to these breakthroughs in infrared technology, infrared astronomy has developed more rapidly than any other field of astronomy and continues to bring us exciting new views of the universe.

Background & Technology Index | Early Infrared Astronomy | New Technology | Ground Based Infrared Observatories | Infrared Astronomy Takes Off | Infrared Astronomy From Earth's Orbit

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