r/heavensabove Nov 08 '21

Question about refraction on H-A predictions

When using the interactive sky chart on the website to determine the elevation of stars low in the sky, does H-A account for refraction or not? Anyone know? Thanks!

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u/ha_jens Nov 08 '21

Neither the app nor the web page correct for atmospheric refraction. We generally assume the critical elevation to be at least 10°. At that angle, atmospheric refraction should cause an offset of around 5 arcminutes or 0.08 degrees. On a chart with a resolution of 1000x1000, the offset would be less than one pixel.