Astronomical Distances:
This program is meant to help you get a feel
for astronomical distances, which are large and difficult to comprehend.
Imagine that you are in a spaceship. Choose your speed and see how long
it takes to get to some of the most interesting places in the Universe!
Let's Go!

Astronomical Sizes:
In order to understand the size of objects in
the Universe it is helpful to scale them to a smaller size. For instance
a pulsar is roughly the size of Washington D.C. But how big would a pulsar
be if the Earth was the size of a baseball? Click here, Astronomical
Sizes, to create scaled models of the Universe for yourself.

Scientific Notation:
Scientific notation allows you to represent very
large or very small numbers in a compact form. Your calculator converts
to scientific notation when you multiply two very large numbers together.
Practice working with Scientific
Notation and quiz yourself!

Working With Equations:
Many important laws of science can be written
as algebraic equations with different variables representing different
physical quantities. How do we decipher what an equation is telling us?
One way is to determine how one side of the equation is affected when a
variable is changed. Click here to practice Working
With Equations.

Universe Timeline:
When would the Earth have formed if the entire
history of the Universe was squeezed into the length of a year? A week?
A day? Just how long is two thousand years when compared with the history
of life on Earth? Using the Universe
Timeline you can explore the history of the cosmos in timescales you
can actually have a feel for.
 
Planetary Calculator:
Compare the sizes, spin periods, surface
gravity, and other data for the eight planets of our Solar
System plus dwarf planet Pluto. Convert to your favorite units and define your own
formulae. Calculations are easy with the
Planetary
Calculator.

Satellite Calculators:
Compare physical and orbital data for all
satellites of the planets. Which moon is largest? Which has the
strongest surface gravity? These calculators operate on multiple moons
simultaneously making comparisons easy. Explore the Solar System's 70
largest and closest moons with
the Regular Satellite
Calculator and more than 100 more distant moons with
the Irregular Satellite
Calculator.

Solar Systems Visualizer
The Solar System consists of rocky terrestrial
planets, gaseous outer planets, asteroids, comets, and Kuiper Belt objects.
All of these objects follow their own independent orbits around the
Sun. Hundreds of satellites circle the planets, and hundreds of planets
have been found around others stars. Watch the orbits of all of these
objects with the
Solar Systems Visualizer.
DEPRECATED

The Life of the Sun
Since its birth 4.5 billion years ago, the
Sun has grown slowly larger and brighter with each four Hydrogen
nuclei that it fuses into Helium. Billions of years from now, it will
swell into a red giant and engulf the inner planets. Using up the last
of its nuclear fuel, the Sun will finally collapse into an Earthsized
white dwarf.
Animate the Sun!
DEPRECATED

Historical Viewers
Planetary Orbits:
Our Solar System!
Satellite Orbits:
Show me the moons!
Planetary Orbits: Other Solar Systems
DEPRECATED

Star Race
Which stars burn though their fuel fastest? Enter stars of different
masses into the PanGalactic
Star Race
and find out!
DEPRECATED


Orbital Elements
An asteroid or comet moving subject to the Sun's
gravity has an orbit shaped like a circle, an ellipse, a parabola, or a
hyperbola. What type of orbit depends on the value of the orbital elements,
quantities that determine the size, shape, and orientation of the orbit
in space. Use these two orbital viewers to see how the appearance of an
orbit depends on the values of the orbital elements.
Orbits in a plane:
Orbital Elements (2D)
More General Orbits:
Orbital Elements (3D)

The Solar System
Watch several planets in our Solar System simultaneously
orbit the Sun. Change the orbital parameters of an additional object 
an asteroid or a comet  to see what types of orbits are possible. In the
real Solar System, objects on crossing orbits will eventually collide (Pluto
and Neptune are an exception; if you watch them move you'll notice that
they never come close to one another).
Inner Solar System (with Asteroid)
Outer Solar System (with Comet)
DEPRECATED

Changing the Elements
An orbit can be represented by a position and velocity vector, or by a
set of six orbital elements that describe the size, shape, and
orientation of the orbit in space. Use this tool to convert between
the two.
Changing the Elements

 
Central Force Integrator
A central force, F(r), is one that is directed radially
toward or away from a fixed point. Orbits in timeindependent central force
fields conserve both orbital angular momentum and energy. Explore the types
of orbits that result from these strange force laws!
Newtonian Gravity F(r) = GM/r^{2}
2D Harmonic Oscillator F(r) = r
General Central Force Integrator

ThreeBody Integrator
How does a small object orbit in the combined gravity field
of two large objects?
Watch an asteroid in the Sun Jupiter system
(2D orbits and 3D orbits)!
Investigate planetary orbits around a Binary Star
(2D orbits and 3D orbits)!
Find Solar System stability zones with the
Lagrange Point Explorer

Satellite Integrator
How far away can our moon be before the sun's gravity
pulls it away into heliocentric orbit? Why don't we find any satellites in the
solar system that orbit over their planets' polar regions? Answer these questions
and more by investigating satellite orbits around different planets!
What if the Moon's orbit were ...
Twice as large?
Tilted by 90 degrees?

Extrasolar Planetary Satellite Integrator
Most of the planets discovered outside our solar system
as of 2003 are gas giants not unlike our very own Jupiter and Saturn. These planets
have no solid surfaces, as they're made almost entirely of gas. However, could these
planets have moons orbiting around them? Would such orbits be stable? Answer these
and other questions as you investigate satellite orbits around extrasolar
planets!
Transiting Planet HD209458b

