A large, basin-shaped volcanic depression that is more or less
circular in form. Most volcanic calderas are produced by collapse of the
roof of a magma chamber due to removal of magma by voluminous eruptions or
subterranean withdrawal of the magma, although some calderas may be formed
by explosive removal of the upper part of a volcano.
(Aka Jean Dominique) Italian-born French astronomer. Cassini was the first
director of the Royal Observatory in Paris. He discovered four of
Saturn's moons (Tethys,
Dione, Rhea
and Iapetus) and the major gap in its rings.
Yellow stars which vary in brightness regularly. The time it takes for it to go through one complete brightness cycle tells astronomer how bright the star actually is. They compare its actual brightness with its brightness from Earth and this gives them the approximate distance to the star.
The exposed core of uplifted rocks in complex meteorite impact
craters; the central peak material typically shows evidence of intense
fracturing, faulting and shock metamorphism.
Polish astronomer who advanced the
heliocentric theory that the earth
and other planets revolve around the Sun. This was highly controversial
at the time; the Ptolemaic view of the
universe, which was the prevailing theory for more than 1000 years,
was deeply ingrained in the prevailing philosophy and religion.
1) The upper level of the solar atmosphere,
characterized by low densities and high temperatures (> 1.0E+06 K);
it is not visible from the Earth except during a total eclipse of the
sun or by use of special telescopes called coronagraphs.
2) An ovoid-shaped feature.
Electromagnetic rays of extremely high frequency and energy;
cosmic rays usually interact with the atoms of the atmosphere before
reaching the surface of the Earth. Some cosmic rays come from outside the
solar system while others are emitted from the Sun and pass through
holes in the corona.
The relatively stable portions of continents composed of shield
areas and platform sediments; typically, cratons are bounded by tectonically
active regions characterized by uplift, faulting and volcanic activity.
A major stratigraphic boundry on Earth marking the end of the
Mesozoic Era, best known as the age of the dinosaurs. The boundary
is defined by a global extinction event that caused the abrupt demise
of the majority of all life on Earth.
Rock types made up of crystals or crystal fragments, such as
metamorphic rocks that recrystallized in high temperature or pressure
environments, or igneous rocks that formed from cooling of a melt.
