Glossary
Asteroid: a rock in space that can be
sized between a few feet and several miles wide. Most asteroids in our
solar system are part of a belt between Mars and Jupiter.
Comet: a chunk of frozen gasses, ice, and
rocky debris that orbits the Sun. A comet nucleus is about the size of a
mountain on earth. When a comet nears the Sun, heat vaporizes the icy
material producing a cloud of gaseous material surrounding the nucleus,
called a coma. As the nucleus begins to disintegrate, it also produces a
trail of dust or dust tail in its orbital path and a gas or ion
tail pointing away from the Sun. Comet comas can extend up to a million
miles from the nucleus and comet tails can be millions of miles long.
There are thought to be literally trillions of comets in our solar system
out past Neptune and Pluto, but only once per decade or so does one become
near and bright enough to see easily without binoculars or a telescope.
Galaxy: a system of about 100 billion stars.
Our Sun is a member of the Milky Way Galaxy, which is sometimes just
designated by capitalization: Galaxy. There are billions of galaxies in
the observable universe. Exactly when and how galaxies formed in the
Universe is a topic of current astronomical research.
Law of gravitation: Newton's law of gravitation is a statement
that any particle of matter in the universe attracts any other with a
force varying directly as the masses and inversely as the square of the
distance between them.
Laws of motion: Newton's laws of motion are relation between the
forces acting on a body and the motion of the body, which had been
discovered experimentally by Galileo about four years before Newton was
born.
Newton's first law states that, if a body is at rest or moving at a
constant speed in a straight line, it will remain at rest or keep moving
in a straight line at constant speed unless it is acted upon by a force.
This postulate is known as the law of inertia, and it is basically a
description of one of the properties of a force: its ability to change
rest into motion or motion into rest or one kind of motion into another
kind.
Newton's second law is a quantitative description of the changes
that a force can produce in the motion of a body. It states that the time
rate of change of the velocity (directed speed), or acceleration, is
directly proportional to the force and inversely proportional to the mass
of the body. This is the most important law, and from it all of the basic
equations of dynamics can be derived by procedures developed in the
calculus.
Newton's third law states that the actions of two bodies upon each
other are always equal and directly opposite; reaction is always equal and
opposite to action. The proposition seems obvious for two bodies in direct
contact; the downward force of a book on a table is equal to the upward
force of the table on the book. It is also true for gravitational forces.
Meteor: in particular, the light phenomenon
which results from the entry into the Earth's atmosphere of a solid
particle from space.
Meteorite: a natural object of
extraterrestrial origin (meteoroid) that survives passage through the
atmosphere and hits the ground.
Meteoroid: a solid object moving in
interplanetary space, of a size considerably smaller than a asteroid and
considerably larger than an atom or molecule.
Meteor Shower: a number of meteors
with approximately parallel trajectories. The meteors belonging to one
shower appear to emanate from their radiant.
Occultation: this is when one celestial body, passes in front of
, and obscures another.
Orbit: the path of one body around another due to the influence
of gravity.
Planet: a spherical ball of rock and/or gas
that orbits a star. The Earth is a planet. Our solar system has nine
planets. These planets are, in order of increasing average distance from
the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune,
and Pluto.
Star: a ball of mostly hydrogen and helium
gas that shines extremely brightly. Our Sun is a star. A star is so
massive that its core is extremely dense and hot. At the high stellar core
temperatures, atoms move so fast that they sometimes stick to other atoms
when they collide with them, forming more massive atoms and releasing a
great amount of energy. This process is known as nuclear fusion.
Scientists have not yet been able to use nuclear fusion as a power source
here on earth, but they are trying!
Supernova: the death explosion of a
massive star, resulting in a sharp increase in brightness followed by a
gradual fading. At peak light output, supernova explosions can outshine a
galaxy. The outer layers of the exploding star are blasted out in a
radioactive cloud. This expanding cloud, visible long after the initial
explosion fades from view, forms a supernova remnant . |
