- accretion
- Accumulation of dust and gas into larger bodies
such as stars, planets and moons.
- Adams, John Couch
1819-1892
- English astronomer and mathematician who, at the
age of 24, was the first person to predict the
position of a planetary mass beyond Uranus. But,
unfortunately, Adams did not publish his
prediction. Galle confirmed the existance of
Neptune based on independent calculations done by
Le Verrier.
- albedo
- the ratio of the amount of light reflected by an
object and the amount of incident light; a
measure of the reflectivity or intrinsic
brightness of an object (a white, perfectly
reflecting surface would have an albedo of 1.0; a
black perfectly absorbing surface would have an
albedo of 0.0).
- albedo feature
- A dark or light marking on the surface of an
object that may not be a geological or
topographical feature.
- antipodal point
- the point that is directly on the opposite side
of the planet
- aphelion
- the point in its orbit where a planet is farthest
from the Sun; when refering to objects orbiting
the Earth the term apogee is used; the
term apoapsis is used for orbits around
other bodies. (opposite of perihelion)
- arcuate
- having the form of a bow; curved; arc-shaped
- Arago, Dominique François
Jean 1786 - 1853
- French astronomer and physicist and Director of
the Paris Observatory, who discovered the
phenomenon of the production of magnetism by
rotation
- d'Arrest, Heinrich Louis
- Danish astronomer who assisted Galle with the first
observations of Neptune. After receiving its
predicted position from Le
Verrier, Galle and d'Arrest began searching.
With Galle at the eyepiece and d'Arrest reading
the chart, they scanned the sky and checked that
each star seen was actually on the chart. Just a
few minutes after their search began, d'Arrest
cried out, "That star is not on the
map!" and earned his place in the history
books.
- asteroid
- (also "planetoid") a medium-sized rocky
object orbiting the Sun; smaller than a planet,
larger than a meteoroid
- asteroid number
- asteroids are assigned a serial number when they
are discovered. It has no particular meaning
except that asteroid N+1 was discovered after
asteroid N.
- astronomical unit (AU)
- = 149,597,870 km; the
average distance from the Earth to the Sun.
1 AU is a long way -- at 100 miles per hour (160
kph) it would take over 100 years to go 1 AU.
- atmosphere
- = 1.013 bars = 1.03
kg/cm2 = 14.7 pounds per square inch, standard
atmospheric pressure at sea level on Earth.
- aurora
- a glow in a planet's ionosphere caused by the
interaction between the planet's magnetic field
and charged particles from the Sun
- aurora borealis
- the "Northern Lights"; caused by the
interaction between the solar wind, the Earth's
magnetic field and the upper atmosphere. A
similar effect happens in the southern hemisphere
where it is known as the aurora australis.
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