Radar astronomy: Difference between revisions

The strength of the [[radar]] return signal is [[radar#Radar range equation|proportional to the inverse fourth-power of the distance]]. Upgraded facilities, increased [[transceiver]] power, and improved apparatus have increased observational opportunities.

Radar techniques provide information unavailable by other means, such as testing [[general relativity]] by observing [[Mercury (planet)|Mercury]]<ref>{{cite conference |title=Radar and spacecraft ranging to Mercury between 1966 and 1988 |author=Anderson, John D. |author2=Slade, Martin A. |author3=Jurgens, Raymond F. |author4=Lau, Eunice L. |author5=Newhall, X. X. |author6=Myles, E. |journal=Proceedings of the Astronomical Society of Australia |conference=IAU, Asian-Pacific Regional Astronomy Meeting, 5th, Proceedings |location=Sydney, Australia |date=July 1990 |type=Held July 16–20, 1990 |publisher=Astronomical Society of Australia |issn=0066-9997 |volume=9 |issue=2 |pages=324 |bibcode=1991PASAu...9..324A }}</ref> and providing a refined value for the [[astronomical unit]].<ref name="SP4218"/> [[Radar imaging|Radar images]] provide information about the shapes and surface properties of solid bodies, which cannot be obtained by other ground-based techniques.

[[File:ADU-1000-34.jpg|thumb|250px|Early planetary radar [[Pluton (complex)|Pluton]], USSR, 1960]]

Relying upon high-powered terrestrial radars (of up to one MW[[megawatt]]),<ref>{{cite web |url=http://www.naic.edu/~nolan/radar/radarstatus.html |title=Arecibo Radar Status |author=<!--Staff writer(s); no by-line.--> |access-date=22 December 2012}}</ref>), radar astronomy is able to provide extremely accurate [[Astrometry|astrometric]] information on the structure, composition and movement of Solar System objects.<ref>{{cite web |url=http://echo.jpl.nasa.gov/introduction.html |title=Asteroid Radar Research Page |last1= Ostro |first1= Steven |date=1997 |publisher= JPL |access-date=22 December 2012}}</ref> This aids in forming long-term predictions of [[asteroid impact|asteroid-Earth impacts]], as illustrated by the object [[99942 Apophis]]. In particular, optical observations measure where an object appears in the sky, but cannot measure the distance with great accuracy (relying on [[parallax]] becomes more difficult when objects are small or poorly illuminated). Radar, on the other hand, directly measures the distance to the object (and how fast it is changing). The combination of optical and radar observations normally allows the prediction of orbits at least decades, and sometimes centuries, into the future.

In August 2020 the Arecibo Observatory ([[Arecibo Observatory|Arecibo Planetary Radar]]) suffered a structural cable failure, leading to the collapse of the main telescope in December of that year.<ref name="NSFrelease20-010">{{cite web |title=Giant Arecibo radio telescope collapses in Puerto Rico|url=https://www.theguardian.com/world/2020/dec/01/arecibo-radio-telescope-collapses-puerto-rico |website=www.theguardian.com |date=December 2020 |access-date=March 5, 2021 |language=en }}</ref>

|doi-access=free }} Using further analysis, this gives a refined figure of {{val|149598845|250|u=km}}.</ref> Once the correct value was known, other groups found echos in their archived data that agreed with these results.<ref name="SP4218"/>

While operational the Arecibo Observatory provided information about earthEarth threatening comet and asteroid impacts, allowing impact and near miss predictions decades into the future such as those for [[99942 Apophis|Apophis]] and other bodies.<ref name="NSFrelease20-010"/> Being smaller the [[Goldstone Solar System Radar]] is less sensitive and unable to provide the same predictive capacity.

* [http://www.planetary.org/blog/article/00003248/ How radio telescopes get images of asteroids] {{Webarchive|url=https://web.archive.org/web/20120125070636/http://www.planetary.org/blog/article/00003248/ |date=2012-01-25 }}

* {{cite web |url= http://www.naic.edu/%7Epradar/pradar.htm |title=Planetary Radar at Arecibo Observatory |publisher=NAIC |access-date=2008-05-15 |archive-date=2008-05-14 |archive-url=https://web.archive.org/web/20080514034816/http://www.naic.edu/%7Epradar/pradar.htm |url-status=dead }}