Space Radar Lab

Tiny space simulators

Orbits and gravity

• Binary Dance

  Two stars really orbit a point between them, closer to the heavier one.

• Comet Tail Compass

  A comet's tail always points away from the Sun, even when the comet is leaving.

• Five Parking Spots (Lagrange Points)

  In the rotating frame of two bodies there are five spots where a third thing can stay still.

• Gravity Slingshot Steal

  A spacecraft can steal a little of a planet's speed by swinging past it.

• Gravity Well Rubber Sheet

  Mass bends the pattern of space-time like a ball in a stretched sheet, and light or marbles follow the dips.

• Janus and Epimetheus

  Two Saturn moons share nearly one orbit and swap places every four years without colliding.

• Kepler Equal Areas

  A planet sweeps out equal areas in equal times, so it speeds up as it nears the Sun.

• Mercury Rosette

  Mercury's orbit slowly turns, and Newton alone could not explain all of it.

• Moons in Step

  Io, Europa and Ganymede orbit Jupiter in a 4:2:1 beat, and their tugs keep the pattern locked.

• One Launch, Four Orbit Shapes

  Circle, ellipse, parabola and hyperbola are all the same orbit with different speeds.

• Orbit Painter

  Each throw gets one push, then gravity bends the path into an orbit, a plunge into the star or an escape.

• Orbit Zoo

  The higher a satellite flies, the slower it goes and the longer its lap.

• The ISS Always Falls

  The Space Station is dragged down a little every day and must be pushed back up.

• The Moon Spins to Match

  Over time tides slow a moon's spin until it faces its planet with one side forever.

• Three Bodies on a Figure Eight

  Three equal stars can chase each other along one figure-eight path forever.

• Throw It Faster

  Throw a ball faster and it lands farther away; at about 7.9 km/s the ground curves away as fast as the ball falls, and it never lands.

Planets and moons

• Greenhouse Dial: Why Venus Is Hot

  A thick CO2 blanket can heat a planet far above what its sunlight alone would do.

• Io: The Squeezed Moon

  Jupiter's tug squeezes Io like a stress ball, heating it enough to power hundreds of volcanoes.

• Mercury Double Sunrise

  On Mercury the Sun can rise, stop, retreat and rise again because of its spin and orbit.

• Roche Limit Shredder

  A moon that gets too close to its planet is torn apart by tides, which is how rings can form.

• Saturn Rings Edge-On

  Saturn's rings are 280,000 km wide yet in places only about ten metres thick.

• Tilt Makes the Seasons

  Earth's tilt, not its distance, makes summer and winter.

• Two Tides, Not One

  The Moon pulls the oceans into two bulges, so tides come twice a day.

• Venus Day Race

  Venus spins once in 243 Earth days and circles the Sun in 225, so its day is longer than its year.

Scale and distance

• Asteroid Belt Is Not Crowded

  Despite pictures, the asteroid belt is almost empty between rocks.

• Earth From the Sun, Shrinking

  From farther out Earth shrinks from a ball to a single pixel.

• Earths in Jupiter

  More than 1,300 Earths would fit inside Jupiter's volume.

• From Ground to Space in 100 km

  Space is only about 100 km up: roughly the drive between two cities.

• Milky Way Address

  Earth is about 27,000 light-years from the centre of our galaxy, in a quiet outer arm.

• Nearest Star by Voyager

  At Voyager's speed the nearest star would take tens of thousands of years.

• Planets Fit Moon Gap

  The other seven planets laid side by side almost fit in the gap between Earth and the Moon: not quite at the average distance, yes at the farthest.

• Powers of Ten Zoom Out

  Zoom out by factors of ten and Earth, solar system, stars and galaxy fall away in seconds.

• The Solar System Is Mostly Empty

  To scale, planets are specks separated by huge gaps.

• The Sun as a Marble

  Shrink the Sun to a marble and Earth is a grain of sand several metres away.

• Voyager Odometer

  Voyager 1 has been travelling since 1977 and is still the farthest thing humans made, at 17 km/s.

• Walk the Solar System

  If the Sun were at your door, Neptune would be a long walk away.

• Your Closest Stars

  The nearest stars are enormous distances away and mostly dim red dwarfs.

Light and time

• Crossing the Galaxy at Light Speed

  A beam of light needs about 87,000 years to cross the Milky Way's disc, longer than human history.

• Doppler Siren Waves

  Waves bunch up in front of a moving source and stretch behind it, changing pitch or colour.

• Inverse Square Flashlight

  Light spreads as it travels, so at twice the distance it is four times dimmer.

• Light Speed Road Trip

  Sunlight takes about 8 minutes to reach Earth and over four hours to reach Neptune.

• Redshift Stripes

  The faster a galaxy flies away, the more its light shifts toward red.

• Stars Bunch Up Ahead

  At near light speed the stars crowd into a bright tunnel in front of you.

• The Sun Vanishes

  If the Sun vanished, we would keep seeing it and keep orbiting for 8 minutes 19 seconds.

Rockets and spaceflight

• Aerobraking Dip

  A probe can shrink its orbit by dipping into the thin upper air, saving fuel.

• Delta-v Subway Map

  Moving around the solar system is like a metro map where each line costs a number of km/s.

• Free-Return Loop to the Moon

  A spacecraft can swing around the Moon and come back to Earth without extra fuel.

• Ion Drive vs Chemical Rocket

  With the same fuel, an ion engine pushes weakly for years and ends up faster than a single chemical burst.

• Mars Launch Window

  You can only launch to Mars cheaply when the planets line up, once every 26 months.

• Reentry Heat: Speed Squared

  Slowing from orbit turns a huge amount of energy into heat, because it scales with speed squared.

• Rocket Equation

  Each extra km/s of speed costs a fifth of what is left, so a rocket bound for orbit is almost all fuel.

• Solar Sail Surf

  Sunlight pushes a thin sail a tiny bit all the time, and that adds up to high speed.

• Staging: Drop the Dead Weight

  Dropping empty tanks lets the rest of a rocket go much faster than one big tank could.

• To Catch Up Slow Down

  In orbit, to catch a craft ahead you drop to a lower orbit, which is faster.

Stars and their lives

• Cepheid Cosmic Yardstick

  A pulsing star's period tells you its true brightness, so you can tell how far away it is.

• Element Factory

  Heavier elements are made in stars in layers, ending at iron.

• Planet Shadow: Transit Light Curve

  When a planet crosses its star the star dims a little, and that is how we found thousands of worlds.

• Pulsar Lighthouse

  A pulsar is a spinning dead star that sweeps a beam past Earth like a lighthouse.

• Sunspot Cycle Counter

  Sunspots rise and fall every 11 years, with storms at the peak.

• Supernova Shockwave

  A massive star's core collapses and the outer layers blast away within seconds.

• What Happens to Our Sun

  In about five billion years the Sun swells into a red giant and swallows the inner planets.

• Wobbling Star

  A planet pulls its star in a little circle, shifting its light blue and red.

Sky from Earth

• Mars' Loop in the Sky

  Planets seem to loop backward as faster Earth overtakes them.

• Meteor Shower Radiant

  Meteors in a shower look like they come from one point because the streams are parallel.

• Midnight Sun

  Above the Arctic Circle the Sun doesn't set for weeks in summer.

• Moon Phases From Above

  The Moon is always half lit; the phase is how much of the lit half faces us.

• Star Trails by Latitude

  The sky spins around different points depending on where you stand, from the pole to the equator.

• Two Eclipses One Geometry

  Solar eclipses happen when the Moon is between us and the Sun; lunar eclipses when Earth is between.

• Venus Phases (Galileo's Proof)

  Venus shows phases like the Moon, proving it circles the Sun, not us.

Cosmology and black holes

• Black Hole Lens in 2D

  A black hole bends light around itself, so a background star can show up twice or as a ring.

• Dark Matter Rotation Curve

  Stars at the edge of galaxies orbit nearly as fast as inner ones, which suggests unseen mass holds them.

• Galaxy Merger Dance

  Galaxies can collide and pass through each other, with their stars rarely touching.

• Spaghettification

  Falling feet-first into a black hole, your feet are pulled harder than your head and you are stretched.

• Time Freezes at the Horizon

  Seen from afar, a clock falling into a black hole ticks slower and slower and never quite crosses.

• Universe Timeline Scrub

  The universe is 13.8 billion years old, and humans arrived in the last sliver.