Astronomy — The Sun, Our Star

Accessibility: This is the accessible version of the lab, built following WCAG 2.1 AA guidelines. It adds screen-reader support, full keyboard navigation, and text descriptions of the interactive diagrams. If you encounter any barrier, please let us know through e2innovations.ai so we can address it.

Theory — The Sun, Our Star

The Sun is an ordinary star: a vast ball of hot plasma held together by gravity and powered from its core.

1. Structure

From the centre outward: the core, where energy is generated; the radiative zone and convective zone, which carry energy to the surface; the photosphere, the visible surface; and above it the thin chromosphere and the vast, hot corona.

2. Energy generation

In the core, at about 15 million kelvin, hydrogen nuclei fuse into helium through the proton-proton chain. A little mass is lost in each reaction and converted to energy by E = mc². This fusion has powered the Sun for about 4.6 billion years and will continue for roughly 5 billion more.

3. Sunspots and the solar cycle

Sunspots are cooler, darker patches on the photosphere where strong magnetic fields suppress convection. Their number rises and falls in an 11-year cycle, and over a cycle they migrate from higher latitudes toward the equator.

4. Rotation from sunspots

Because sunspots are carried around by the Sun’s rotation, tracking one across the disk measures how fast the Sun turns. If a spot moves through a change in longitude ΔL over a time Δt, the rotation period is:

Rotation period from a sunspot P = 360° × Δt / ΔL
The Sun rotates in about 25 days at its equator.

The Sun does not rotate as a solid body: the equator turns faster than the poles, a behaviour called differential rotation.

Apparatus

Solar observing uses instruments to image the disk safely, spread its light, and map its magnetism. In the simulation these are modelled, but the readings match what each instrument would give.

Solar disk

A safely filtered image of the photosphere showing sunspots and their motion.

Prominence loop

A loop of glowing gas suspended above the surface by magnetic fields.

Spectrohelioscope

Images the Sun in a single spectral line to reveal the chromosphere and flares.

Projection screen

A safe way to view the Sun by projecting its image through a telescope onto a screen.

Magnetometer

Maps the strong magnetic fields that produce sunspots and the solar cycle.

Coronagraph

Blocks the bright disk so the faint corona and prominences can be seen.

Instructions

Work through both tabs. Calculate first by hand, then press the button to compare.

Part A — Solar rotation from a sunspot

Step the days forward and read the sunspot’s longitude on each day.
Take two observations, find the change in longitude ΔL and the elapsed time Δt, and compute P = 360° × Δt / ΔL by hand.
Enter your rotation period and press Check.

Part B — Sunspots and the cycle

Move through the solar cycle and watch the sunspot number and latitude change.
Predict the length of the sunspot cycle, then press Check.

Simulation

Day

Your rotation period (days)

Year in cycle

Predicted cycle length (years)

Team Questions

1. The Sun generates its energy by:

Burning coal and gas Fusing hydrogen into helium in its core Chemical reactions in the corona Reflecting starlight

2. Sunspots appear darker than their surroundings because they are:

Cooler, where magnetic fields suppress convection Holes through the Sun Clouds of dust Shadows of planets

3. The Sun’s equator rotates faster than its poles, a behaviour called:

Solid rotation Precession Differential rotation Nutation

Example Report

Worked example: the Sun’s rotation period

On day 0 a sunspot is at longitude 20°; on day 6 it has moved to 105°.

The change is ΔL = 85° over Δt = 6 days, a rate of about 14.2 degrees per day.

P = 360° × Δt / ΔL = 360 × 6 / 85 ≈ 25.4 days. The Sun’s equatorial rotation period is about 25 days, so the measured and accepted values agree. Tracking the spot and computing the period is the calculate-then-compare core of the lab.

The Sun, Our Star