PhysicsUK
Astrophysics & Cosmology Lab

OBSERVATION
LIVE EVIDENCE MODEL / INSTRUMENT

Choose an investigation

Setup and notebook are saved on this device. Playback resumes paused.

Experiment controls

Guided investigation
    Model and limitations

    Keyboard and accessibility

    Tab reaches all controls. Arrow keys adjust native sliders. On the graph, arrows move its cursor; H–R uses left/right for temperature and up/down for luminosity. Space runs or pauses a focused canvas, C captures and R restarts. Escape cancels a drag or closes a panel. Playback respects reduced-motion settings by avoiding decorative animation; scientific motion remains available through Run, Pause and Step.

    Sources and curriculum

    Observation notebook

    Fits use the latest compatible series and need three distinct x values. Green points are captured observations; gold is the unweighted fit.

    Find Hubble’s constant

    PUPIL INVESTIGATION · SYNTHETIC GALAXY SURVEY

    Measure at least five galaxies over a wide distance range. Distances are supplied independently. Your calculated velocities produce your graph; the model velocities are hidden in this mode.

    1. Measure the spectrum

    Recorded observed wavelength:

    Rest Hα: 656.28 nm. Close this notebook, align the wavelength cursor with the observed line, and select Record wavelength. Repeat measurements replace that galaxy’s row.

    2. Calculate and plot

    z = (λobserved − λrest) / λrest   ·   v ≈ cz, using c = 299,792 km/s.

    3. Fit a line and estimate H₀

    After plotting three or more galaxies, use the two fit sliders on the bench. Aim for a line through the middle of the scatter; it need not join every point. Choose two far-apart points on that line and calculate Δv / Δd.

    Evaluate your investigation

    How would a wavelength error change the velocity? Why are widely separated galaxies useful for the gradient? Repeat the survey with peculiar velocities enabled and discuss the scatter. The low-redshift v ≈ cz approximation is appropriate for this dataset; it is not a general formula for distant cosmological redshifts. The comparison fit uses your data, including any calculation mistakes.