Understanding stellar parallax
Turn a star’s annual parallax into a distance in parsecs and light-years.
The idea behind it
As Earth moves around the Sun, a nearby star appears to shift against distant background stars. The annual parallax is half of the total angular shift between opposite points in Earth’s orbit.
The relationship to remember
1 / 0.1 arcseconds = 10 parsecs = 32.62 light-years.
Make your own discovery
Reduce the parallax angle by a factor of ten. The inferred distance increases by the same factor.
Try the interactive lab ↗What this model leaves out
The standard small-angle parsec relation with exact input. The diagram exaggerates angles and compresses distances. Real measurements include uncertainty and corrections.
Check your understanding
What is a parsec?
A parsec is the distance corresponding to one arcsecond of annual parallax, approximately 3.26 light-years.
Why are distant stars harder to measure?
Their parallax angles are smaller, so a fixed angular uncertainty represents a larger fraction of the measurement.
Continue with the formula reference or test yourself in space practice.