Editing Length contraction (section)

==Visual effects==
{{Main|Terrell rotation}}
[[File:Lorentz contractie - mural Leiden, 2017.jpg|upright=1.35|thumb|Formula on a wall in Leiden, Netherlands. Lorentz was chair of theoretical physics at the [[University of Leiden]] (1877–1910).]]
Length contraction refers to measurements of position made at simultaneous times according to a coordinate system. This could suggest that if one could take a picture of a fast moving object, that the image would show the object contracted in the direction of motion. However, such visual effects are completely different measurements, as such a photograph is taken from a distance, while length contraction can only directly be measured at the exact location of the object's endpoints. It was shown by several authors such as [[Roger Penrose]] and James Terrell that moving objects generally do not appear length contracted on a photograph.<ref>{{cite journal |author=Kraus, U. |year=2000 |title=Brightness and color of rapidly moving objects: The visual appearance of a large sphere revisited |journal=American Journal of Physics |volume=68 |issue=1 |pages=56–60 |doi=10.1119/1.19373|url = http://www.tempolimit-lichtgeschwindigkeit.de/sphere/sphere.pdf |bibcode = 2000AmJPh..68...56K }}</ref> This result was popularized by [[Victor Weisskopf]] in a Physics Today article.<ref>{{Cite journal |doi = 10.1063/1.3057105|title = The visual appearance of rapidly moving objects|journal = Physics Today|volume = 13|issue = 9|pages = 24–27|year = 1960|last1 = Weisskopf|first1 = Victor F.|bibcode = 1960PhT....13i..24W|s2cid = 36707809}}</ref> For instance, for a small angular diameter, a moving sphere remains circular and is rotated.<ref>{{cite book|last=Penrose|first=Roger|title=The Road to Reality|year=2005|publisher=Vintage Books|location=London|isbn=978-0-09-944068-0|pages=430–431}}</ref> This kind of visual rotation effect is called Penrose-Terrell rotation.<ref>{{Cite web|url=https://math.ucr.edu/home/baez/physics/Relativity/SR/penrose.html|title=Can You See the Lorentz–Fitzgerald Contraction?|website=math.ucr.edu}}</ref>