astronomy

List of Earth-crossing asteroids

List of Earth-crossing asteroids is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand List of Earth-crossing asteroids rather than just read about it. In short: An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here.

Key takeaways

List of Earth-crossing asteroids belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect List of Earth-crossing asteroids to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of List of Earth-crossing asteroids from memory before moving on to harder problems.

Reference excerpt

An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids. (See also the Amor asteroids.) An asteroid with an Earth-crossing orbit is not necessarily in danger of colliding with Earth. The orbit of an Earth-crossing asteroid may not even intersect with that of Earth. This apparent contradiction arises because many asteroids have highly inclined orbits, so although they may have a perihelion less than that of Earth, their paths can never cross. An asteroid for which there is some possibility of a collision with Earth at a future date and which is above a certain size is classified as a potentially hazardous asteroid (PHA). Specifically, an asteroid is a PHA if its Earth minimum orbital intersection distance (MOID) is <0.05 AU and its absolute magnitude is 22 or brighter. The concept of PHA is intended to replace the now abandoned strict definition of ECA (Earth-crossing asteroid) which existed for a few years. Determining if an asteroid was an ECA required calculation of its orbits millennia into the future, including planetary gravitational perturbations, to assess whether a collision with Earth was possible and this has proved to be impractical. Having a small MOID is not a guarantee of a collision. On the other hand, small gravitational perturbations of the asteroid around its orbit from planets that it passes can significantly alter its path. For instance, 99942 Apophis will approach Earth so closely in 2029 that it will get under the orbit of the Earth's geostationary satellites. Of the Earth-crossing asteroids, 3753 Cruithne is notable for having an orbit that has the same period as Earth's.

List

Notes: † outer-grazer

See also Earth-grazing fireball List of asteroid close approaches to Earth Asteroid impact avoidance List of Mercury-crossing minor planets List of Venus-crossing minor planets List of Mars-crossing minor planets List of Jupiter-crossing minor planets List of Saturn-crossing minor planets List of Uranus-crossing minor planets List of Neptune-crossing minor planets

References

External links Very Close Approaches (<0.01 AU) of PHAs to Earth 1900–2200 Upcoming Close Approaches (<0.10 AU) of Near-Earth Objects to Earth Table of next close approaches to the Earth -Sormano Astronomical Observatory Small Asteroids Encounter List -Sormano Astronomical Observatory Minor Body Priority List -Sormano Astronomical Observatory IAU-MPC Close Approaches to the Earth within 0.2 AU -Minor Planet Center

Illustrations

List of Earth-crossing asteroids: Flyby of the near-Earth asteroid 2004 FH in March 2004. The other object that flashes by is an artificial satellite. Images were by Stefano Sposetti and composite by Raoul Behrend of Geneva Observatory — Flyby of the near-Earth asteroid 2004 FH in March 2004. The other object that flashes by is an artificial satellite. Images were by Stefano Sposetti and composite by Raoul Behrend of Geneva Observatory

Worked examples

Example 1 — a first encounter with List of Earth-crossing asteroids

Start with the simplest possible case. Write down what List of Earth-crossing asteroids claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to List of Earth-crossing asteroids before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about List of Earth-crossing asteroids ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of List of Earth-crossing asteroids

In research: List of Earth-crossing asteroids appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses List of Earth-crossing asteroids in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: List of Earth-crossing asteroids is common in secondary-school and first-year university syllabi. It links to neighbouring topics Earth-crossing asteroids, Lists of minor planets, Minor planet groups and families, so understanding it makes those chapters shorter.
In everyday life: Look for List of Earth-crossing asteroids outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study List of Earth-crossing asteroids in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what List of Earth-crossing asteroids means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain List of Earth-crossing asteroids out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is List of Earth-crossing asteroids in simple terms?

An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here.

Why does List of Earth-crossing asteroids matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study List of Earth-crossing asteroids?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on List of Earth-crossing asteroids.