Editing Geostationary orbit (section)

=== Communications ===
Geostationary communication satellites are useful because they are visible from a large area of the earth's surface, extending 81° away in latitude and 77° in longitude.<ref name="eisemann"/> They appear stationary in the sky, which eliminates the need for ground stations to have movable antennas. This means that Earth-based observers can erect small, cheap and stationary antennas that are always directed at the desired satellite.<ref name="smad"/>{{rp|537}} However, [[Latency (engineering)|latency]] becomes significant as it takes about 240&nbsp;ms for a signal to pass from a ground based transmitter on the equator to the satellite and back again.<ref name="smad"/>{{rp|538}} This delay presents problems for latency-sensitive applications such as voice communication,<ref>{{cite web|url=http://www.isoc.org/inet96/proceedings/g1/g1_3.htm |title=The Teledesic Network: Using Low-Earth-Orbit Satellites to Provide Broadband, Wireless, Real-Time Internet Access Worldwide |first=Daniel |last=Kohn |publisher=Teledesic Corporation, USA |date=March 6, 2016}}</ref> so geostationary communication satellites are primarily used for unidirectional entertainment and applications where low latency alternatives are not available.<ref name="wiley">{{cite book|chapter=Satellite Communications|first=Roger L.|last=Freeman|date=July 22, 2002|publisher=American Cancer Society|doi=10.1002/0471208051.fre018|title = Reference Manual for Telecommunications Engineering|isbn = 0471208051}}</ref>

Geostationary satellites are directly overhead at the equator and appear lower in the sky to an observer nearer the poles. As the observer's latitude increases, communication becomes more difficult due to factors such as [[atmospheric refraction]], Earth's [[thermal radiation|thermal emission]], line-of-sight obstructions, and signal reflections from the ground or nearby structures. At latitudes above about 81°, geostationary satellites are below the horizon and cannot be seen at all.<ref name="eisemann">{{cite journal|url=http://www.ngs.noaa.gov/CORS/Articles/SolerEisemannJSE.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.ngs.noaa.gov/CORS/Articles/SolerEisemannJSE.pdf |archive-date=2022-10-09 |url-status=live|page=123|title=Determination of Look Angles To Geostationary Communication Satellites|first1=Tomás |last1=Soler|first2= David W. |last2=Eisemann|journal=Journal of Surveying Engineering |volume=120|issue=3|date=August 1994|issn=0733-9453|access-date=April 16, 2019|doi=10.1061/(ASCE)0733-9453(1994)120:3(115)}}</ref> Because of this, some [[Russia]]n communication satellites have used [[elliptic orbit|elliptical]] [[Molniya orbit|Molniya]] and [[Tundra orbit|Tundra]] orbits, which have excellent visibility at high latitudes.<ref name=seh>{{cite book|page=416|url=https://books.google.com/books?id=2ZNxDwAAQBAJ&q=molniya+orbit+OKB-1+history&pg=PA416|isbn=978-1-85109-514-8|title = Space Exploration and Humanity: A Historical Encyclopedia|volume=1|author=History Committee of the American Astronautical Society |editor-first=Stephen B. |editor-last=Johnson|publisher = Greenwood Publishing Group|date = August 23, 2010|access-date=April 17, 2019}}</ref>