Probability experiment lab
Run repeatable coin, die or card-rank experiments. Increasing the trial count usually reduces random fluctuation, but it does not force the observed percentages to equal theory.
Science experiments
Browse practical tools, sky models and country-specific scenarios. Each tool explains its method and limitations.
How it works
Run repeatable coin, die or card-rank experiments. Increasing the trial count usually reduces random fluctuation, but it does not force the observed percentages to equal theory. Explore why shared birthdays become likely in a moderately sized group. The model deliberately treats all 365 dates as equally likely.
Select a country independently of the interface language. Rates and fees are supplied by you unless an official dated source is explicitly stated.
Shared birthday experiment
Explore why shared birthdays become likely in a moderately sized group. The model deliberately treats all 365 dates as equally likely.
Monty Hall experiment
Test staying versus switching under the classic host rules. If the host opens doors without knowing the prize or offers switches selectively, this model no longer applies.
Bayesian probability explorer
See how a prior probability and a signal interact. A signal with false positives can still have a low posterior probability when the original event is rare.
Survey uncertainty explorer
Explore uncertainty around a yes-or-no survey proportion. The interval describes random sampling variation under the model, not whether the sample represents the population.
Scale the Solar System
Build a tabletop or outdoor Solar System scale model. Planet diameters and orbital distances share a scale, which makes the large gaps between planets visible.
Light and sound travel
Compare light and sound travel over the same distance. Sound depends on the medium and conditions, while the light calculation assumes a vacuum.
Ideal pendulum simulator
Explore how pendulum length and gravity affect the ideal period. The animation uses a small swing and does not model damping or a large-amplitude correction.
Gear and pulley ratios
Compare input and output rotation for a pair of gears or pulleys. Tooth count and diameter are alternatives within the selected model; use consistent units.
Queue waiting simulator
Observe how random arrivals and service times create waiting. High offered utilization can produce long queues even when average service seems fast enough.
Telescope magnification and field of view
Compare an eyepiece with your telescope. See magnification, approximate sky coverage and exit pupil together.
Star photograph exposure estimate
Estimate an initial exposure for an untracked wide-angle star photograph, then check a test image for trails.
Planet altitude and azimuth
Locate the Sun, Moon and planets relative to your local horizon at a chosen UTC instant. The coordinates describe the sky, not astrological influence.
Moon rise and set times
Find Moon rise and set events during the selected UTC day at the entered location. Some locations and dates have no event within that day.
Moonless dark-sky sampling
Inspect half-hour samples across a UTC day when the Sun is below astronomical twilight and the Moon is below the horizon.
Planet observing samples
Find half-hour UTC samples when your chosen planet is high enough and the Sun is below civil twilight. Use local weather and a horizon check before observing.
Twenty-four solar terms
Find the instants at which the apparent solar longitude reaches each multiple of 15 degrees during a Gregorian year.
Planetary station calendar
Find changes between direct and retrograde apparent geocentric longitude motion over a bounded date window.
Equatorial coordinate horizon map
Plot objects from your own equatorial coordinates on a north-up local sky diagram and list their altitude and azimuth.
Meteor radiant observing geometry
Compare radiant height, astronomical darkness and Moon height during a 24-hour observing window using coordinates from a current shower notice.
ISS and satellite TLE pass sampler
Compute geometric satellite pass samples from two orbital element lines you provide. The built-in ISS example is historical, dated June 2019; it is not a live prediction.
Planet and local obstruction comparison
Compare a planet track with a skyline you measured, so a geometric rise does not get confused with clearing a building or hill.
Optical airmass and extinction estimate
Estimate why a low object is dimmer through a longer atmospheric path, using an extinction coefficient measured for your conditions.
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