edX
is an online repository of educational courses covering a wide variety of subjects delivered by a number of recognised universities. All of the courses are free to take; if you choose to, you can pay to be assessed and receive a certificate.
I've compiled a list of those that may be of interest to the community:
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Alien Worlds:
The Science of Exoplanet Discovery and Characterization
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Exoplanets:
Exploring the mysteries of exoplanets - planets around other stars.
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Greatest Unsolved Mysteries of the Universe:
Exploring the biggest mysteries of modern astrophysics.
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Relativity and Astrophysics:
Explore the powerful and intriguing connections between astronomy and Einstein’s theory of relativity.
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The Evolving Universe:
A survey of the physical universe and its constituents, including the formation, function, and evolution of stars, galaxies, black holes, quasars, and more.
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The Violent Universe:
Exploring the deadliest places in the universe, from black holes to supernovae.
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Waves and optics:
This course covers the physics of waves on strings, electromagnetic waves, geometrical optics, interference, diffraction, and image formation.
Note that there are other courses including electronics, mathematics, signal analysis, computer programming and general physics that may be of interest so have a look.
(Insert usual guff about my not being associated with edX here...)
  