---
title: "Astronomy starts with a measurement"
description: "Explore stellar positions, photometry, spectra, galaxy colors, telescope arrays and radio pulses through six interactive astronomy courses."
canonical_url: "https://sandboxphysics.com/stories/astronomy/"
language: "en"
page_type: "story"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/stories/astronomy/"
last_modified: "2026-10-28"
---

STARS · LIGHT · MEASUREMENT

# Astronomy starts with a measurement

A point of light gives us a position, a brightness and a spectrum. Change how you observe it, and each tells a different part of the story.

## Start with a star you can move

Begin with geometry, then count the light reaching a detector, then spread that light into colours. Each route connects a visual experiment with a longer explanation and a calculation you can repeat.

01

## [Positions and distances](https://sandboxphysics.com/stories/astrometry/)

Are neighbouring stars really neighbours?

As Earth travels around the Sun, a nearby star traces a small path against the distant sky. Follow that motion to measure distance, then see how uncertainty changes the answer.

[Track a star across a year](https://sandboxphysics.com/labs/stellar-parallax-proper-motion/)

02

## [Measuring starlight](https://sandboxphysics.com/stories/stellar-photometry/)

Did the star fade, or did the background change?

A telescope spreads each star over several pixels. A small aperture loses light; a large one admits neighbours. Move the aperture and measure brightness from the saved pixels.

[Measure a star in a crowded field](https://sandboxphysics.com/labs/crowded-star-photometry/)

03

## [Reading stellar spectra](https://sandboxphysics.com/stories/stellar-spectroscopy/)

Why does one dark line deepen, widen and shift?

A stellar atmosphere absorbs particular colours. Moving atoms shift and broaden those dark lines. Follow one line to separate the effects of temperature, gas column and velocity.

[Change an atmosphere and compare its lines](https://sandboxphysics.com/labs/stellar-absorption-lines/)

04

## [Galaxy colors and redshift](https://sandboxphysics.com/stories/galaxy-colors/)

Can a color give a unique distance?

Old stars, dust and cosmic expansion can all redden a galaxy. Pass a spectrum through five filters, follow competing redshift solutions, then test the method on measured SDSS fluxes.

[Observe a galaxy through five bands](https://sandboxphysics.com/labs/galaxy-colors-photometric-redshift/)

05

## [Telescope arrays and images](https://sandboxphysics.com/stories/interferometric-imaging/)

How does a sparse array constrain an image?

A few telescope pairs measure only part of the sky’s structure. Move a station, change the sampled directions and compare two reconstructions from the same saved signals. The tutorial starts with a measured EHT triangle.

[Move telescopes and compare sky images](https://sandboxphysics.com/labs/stellar-interferometer/)

06

## [Radio pulses in interstellar space](https://sandboxphysics.com/stories/interstellar-radio/)

Why does a flash become a sweep and a tail?

Free electrons delay lower-frequency radio waves. Scattering stretches a flash into a tail. Move the plasma screen and magnetic field, then examine a measured CHIME intensity cutout.

[Send a radio flash through plasma](https://sandboxphysics.com/labs/interstellar-radio-propagation/)

## Follow the light farther

Stellar measurements lead to galaxies and cosmic expansion. Continue with the astronomy evidence stories or the cosmology course.

[How we learned to read the universe](https://sandboxphysics.com/stories/astronomy-gravity/) [Cosmology from expansion to inference](https://sandboxphysics.com/stories/cosmology/)