Today's astro seminar was by Pieter van Dokkum (Yale), about the Dragonfly project and their discovery of large, dark-matter-only-ish galaxies. That is, they have found galaxies that have way fewer stars per unit of dark-matter mass than anything previously. That's exciting. We had lots of discussion during the talk and before about the technical value and also challenges of working with small telescopes, and in particular refractors. van Dokkum put a lot of weight on the existence (in the digital photography world) of nano-scale structured anti-reflection coatings, which are available in (high end) commercial lenses but not in refracting telescopes. He discussed the value of having no supports in the aperture, and no mirrors (yes, mirrors are bad for ultra-low surface brightness). There are many connections between this work and the future coronography we need to do to directly image exoplanets. Dragonfly is a beautiful, sensible, low-cost project that is incredibly successful.

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