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Telescope Field of View Calculator Field Guide: When Exit Pupil, True FOV, and Useful-Magnification Ceiling Decide Whether the Eyepiece You Grabbed Is the One That Actually Works

By xiezixing 2026年9月12日

Your telescope eyepiece math collapses to one rule, the exit pupil has to land where…

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Light-Year & Astronomical Unit Converter Field Guide: When the Parsec Was Built to Match the Arcsecond

By xiezixing 2026年8月16日

A light-year is not a year of light. It is a distance measured in meters,…

Kepler Orbit Solver — Numerically solve Kepler equation M = E − e·sin E for eccentric anomaly, true anomaly, and orbital radius.

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Kepler Orbit Solver: Why M = E − e·sin E Has No Closed Form (And How to Solve It Anyway)

By xiezixing 2026年7月11日

Three numerical methods for Kepler's transcendental equation: Newton-Raphson, bisection, and fixed-point iteration — compared on Earth, Mercury, and a near-parabolic comet orbit.

Telescope Field of View Calculator — 8-inch SCT, 25mm eyepiece, deep-sky framing

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Telescope Field of View Calculator: Why a 25mm Eyepiece Doesn’t Always Show Andromeda

By xiezixing 2026年7月10日

True field of view, exit pupil, and Dawes limit determine what you actually see through any telescope — and the wrong eyepiece math can hide Andromeda in plain sight.