Before we get into the nitty-gritty details of classifications, we need to define some important key terms. These will
come in handy soon.
Aphelion: The point of orbit at which an asteroid is furthest from the Earth.
Perihelion: The point of orbit at which an asteroid is closest to the Earth.
Semi-major axis: The length of the longest radius of an ellipse, that is the greatest
distance between the centre of the ellipse and the perimeter of the ellipse.
Astronomical Unit (au): A unit of length, roughly the distance from Earth to the Sun and
equal to about 150 million kilometers
Amors
Orbits are larger than Earth's but smaller than Mars's.
The semi-major axis is greater than 1 au.
The perihelion is between 1.017 au and 1.3 au.
Apollos
Orbits cross the Earth's but the semi-major axes are bigger.
The semi-major axis is greater than 1 au.
The perihelion is less than 1.017 au.
Atens
Orbits cross the Earth's but the semi-major axes are smaller.
The semi-major axis is less than 1 au.
The aphelion is greater than 0.983 au.
Atiras
Orbits are entirely contained in the Earth's.
The semi-major axis is less than 1 au.
The aphelion is less than 0.983 au.
Click here to move
This is a simulation to help you visualize how many asteroids there are. Blue objects represent parts of rocket bodies.
Yellow objects represent payload (waste ejected from rockets). Grey objects represent general debris and green ones represent
others. Check the box if you want to trigger viewing orbits.
