---
title: 'How to Estimate the Distance to the Sun'
source: 'https://youtube.com/watch?v=gzbFNnTCkqQ'
video_id: 'gzbFNnTCkqQ'
date: 2026-08-10
duration_sec: 91
---

# How to Estimate the Distance to the Sun

> Source: [How to Estimate the Distance to the Sun](https://youtube.com/watch?v=gzbFNnTCkqQ)

## Summary

This video explains a clever geometric method to estimate the distance to the Sun using only observations of the Moon's phases. It clarifies a common misconception about the Half Moon and shows how a simple right triangle can unlock cosmic distances.

### Key Points

- **Using the Moon to Measure the Sun** [00:01] — The video introduces the idea of using the Moon's phases to estimate the distance to the Sun without knowing its size.
- **The Right Angle Is at the Moon** [00:38] — The Half Moon occurs when the side of the Moon facing us overlaps by exactly 90° with the side illuminated by the Sun, meaning the right angle is at the Moon, not at Earth.
- **Half Moon Timing and Sun Distance** [01:05] — Half moons are slightly closer to new moons than to full moons, and the exact timing depends on the Sun's distance.
- **Using the Triangle to Estimate Distance** [01:17] — By drawing a right triangle involving the Earth-Moon distance and the angle at the Moon, you can estimate the Earth-Sun distance.

## Transcript

distance to the Sun without knowing its size and how could you do this on your own you again use the moon you look at phases of the moon so the sun illuminates half of the the moon at any
given time and so we on Earth we also see half the moon but it's a different half um and so because of that we get phases of the moon so sometimes you get over here um and sometimes sometimes you get a half half moon you can pretty much
estimate the distance to the Sun by asking when exactly a Half Moon occurs halfway between a new moon and a full moon but that's actually not true Half
Moon occurs not not when the Moon and the Sun make a right angle at the Earth but actually when the Earth and the Sun make a right angle at the Moon hopefully this makes some sense for us to see a half moon it means that the side of the
moon that we see facing Us overlaps by exactly 90° with the side of the Moon being illuminated by the sun which in turn means we have have a right angle at the spot labeled here half moons are slightly closer to new moons than they
other full moons of course in this graphic the effect is very exaggerated because the sun is being drawn so close to the Earth how far away the sun is determines when exactly that Half Moon occurs the farther away the closer it is
to the true halfway point and if you can walk out that right angle triangle involving the distance of the Moon this is the Sun and