Julian Day Number
About Julian Day
What this tool does
Astronomy tools calculate telescope magnification, orbital periods, escape velocity, habitable zone boundaries, light travel times, parsec-to-light-year conversions, star trail lengths, and satellite visibility windows.
Why use this tool
Amateur astronomers and students need quick reference calculations when planning observations or solving physics problems. Knowing the magnification of an eyepiece-telescope combination, or the escape velocity of a planet, informs both practical stargazing and academic work.
How it works
Magnification divides the telescope's focal length by the eyepiece's focal length. Orbital period uses Kepler's third law. Escape velocity applies the formula v = sqrt(2GM/r). Habitable zone boundaries are estimated from stellar luminosity.
Pro tip
For visual observing, do not exceed 50x magnification per inch of aperture. Higher magnification dims the image and amplifies atmospheric turbulence, making objects harder to see, not easier.
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