There is now very strong evidence that the root cause of these cycles lies in periodic variations in the earth's rotation axis and orbit around the sun. (reddit.com)
These crystals are nanostructured materials in which periodic variations of the refractive index on the length scale of visible light produces a photonic «band gap». (nanotechweb.org)
A month later, follow - up observations with the Lovell radio telescope in Cheshire, UK, revealed periodic variations in the pulsar's signals, indicating the existence of an orbiting companion with the mass of a planet. (newscientist.com)