page_title: Light echo
section_title: V838 Monocerotis
hierarchical_section_title: Light echo / Examples / V838 Monocerotis
caption_attribution_description: English: Successive photos of V838 Monocerotis showing the progress of a light echo. Português: Fotos sucessivas da V838 Monocerotis mostrando o progresso do 'eco de luz'.
context_page_description: A light echo is a physical phenomenon caused by light reflected off surfaces distant from the source, and arriving at the observer with a delay relative to this distance. The phenomenon is analogous to an echo of sound, but due to the much faster speed of light, it mostly only manifests itself over astronomical distances.
  For example, a light echo is produced when a sudden flash from a nova is reflected off a cosmic dust cloud, and arrives at the viewer after a longer duration than it otherwise would have taken with a direct path. Because of their geometries, light echoes can produce the illusion of superluminal motion.
context_section_description: The variable star V838 Monocerotis experienced a significant outburst in 2002 as observed by the Hubble Space Telescope. The outburst proved surprising to observers when the object appeared to expand at a rate far exceeding the speed of light as it grew from an apparent visual size of 4 to 7 light years in a matter of months.
caption: Images showing the expansion of the light echo of V838 Monocerotis. Credit: NASA/ESA.
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