Editing Motion (section)

=== Superluminal motion ===
{{See also|Superluminal motion}}
Some motion appears to an observer to exceed the speed of light. Bursts of energy moving out along the [[relativistic jet]]s emitted from these objects can have a [[proper motion]] that appears greater than the speed of light. All of these sources are thought to contain a [[black hole]], responsible for the ejection of mass at high velocities. [[Light echo]]es can also produce apparent superluminal motion.<ref>{{cite journal |last=Bond |first=H. E. |display-authors=etal |year=2003 |title=An energetic stellar outburst accompanied by circumstellar light echoes |journal=[[Nature (journal)|Nature]] |volume=422 |issue=6930 |pages=405–408 |arxiv=astro-ph/0303513 |bibcode=2003Natur.422..405B |doi=10.1038/nature01508 |pmid=12660776 |s2cid=90973}}</ref> This occurs owing to how motion is often calculated at long distances; oftentimes calculations fail to account for the fact that the speed of light is finite. When measuring the movement of distant objects across the sky, there is a large time delay between what has been observed and what has occurred, due to the large distance the light from the distant object has to travel to reach us. The error in the above naive calculation comes from the fact that when an object has a component of velocity directed towards the Earth, as the object moves closer to the Earth that time delay becomes smaller. This means that the apparent speed as calculated above is ''greater'' than the actual speed. Correspondingly, if the object is moving away from the Earth, the above calculation underestimates the actual speed.<ref>{{cite journal |last1=Meyer |first1=Eileen |date=June 2018 |title=Detection of an Optical/UV Jet/Counterjet and Multiple Spectral Components in M84 |journal=The Astrophysical Journal |volume=680 |issue=1 |page=9 |arxiv=1804.05122 |bibcode=2018ApJ...860....9M |doi=10.3847/1538-4357/aabf39 |s2cid=67822924 |doi-access=free }}</ref>