This visualization shows the orbits of 288 exoplanets, taking eccentricity of the orbit
and Kepler's 2nd law
into account. The orbits of the planets have been scaled to each other. The star in the center is
scaled to the size of our Sun in comparison to the orbits.
The sizes of the planets are scaled as well, but not to the orbits. Otherwise most planets would
become extremely small (smaller than a pixel)
Astronomical Unit (au)
An astronomical unit is a unit of length, roughly the distance from the Earth to the Sun.
However, that distance varies as the Earth orbits the Sun, from a maximum (aphelion) to
a minimum (perihelion) and back again once a year. It is now defined as about 150 million km,
or 93 million miles
Eccentricity
Although some objects follow circular orbits, most orbits are shaped more like
"stretched out" circles: ellipses. An ellipse can be very long and thin,
or it can be like a circle.
The eccentricity of an ellipse describes how round or how "stretched out" an ellipse is.
If the eccentricity is close to one, the ellipse is long and skinny. If the eccentricity
is close to zero, the ellipse is like a circle.
The eccentricity of Earth's orbit is only 0.02, so Earth's orbit is nearly circular.
Many comets have extremely eccentric orbits. Halley's Comet has an orbital eccentricity of almost 0.97!
The star is not at the center of an elliptical orbit. It is a little off to one side,
at a point called a "focus" of the ellipse. Because of this offset the planet moves
closer to and further away from the Star every orbit. The close point in each orbit is
called "perihelion". The far away point is called "aphelion". If an orbit has a large
eccentricity, the difference between the perihelion and aphelion distance
will be large. Earth is only 3% further from the Sun at aphelion than it is at
perihelion. Pluto's eccentricity is 0.25 and its aphelion distance from the Sun is
66% greater than its perihelion distance
1.
Semi-Major Axis
The semi-major and semi-minor axes of an ellipse are radii of the ellipse.
The semi-major axis is the longest radius and the semi-minor axis the shortest.
If they are equal in length then the ellipse is a circle
Data
The data was taken from the Orbit database of exoplanets.org
of exoplanets where the Planetary Radius, Semi-Major Axis, Orbital Period,
Orbital Eccentricity and Effective temperature of the exoplanet's star
are known