The existence of the Earth's galaxy,
the Milky Way, as a separate group of stars, was only proved
in the 20th century, along with the existence of "external"
galaxies, and soon after, the expansion of the universe, seen
in the recession of most galaxies from us. Modern astronomy
has also many exotic objects such as quasars,
pulsars, exoplanets, and black holes. Our solar system orbits
within the Milky Way, a barred spiral galaxy that is a
prominent member of the Local Group of galaxies. It is a
rotating mass of gas, dust, stars and other objects, held
together by mutual gravitational attraction. As the Earth is
located within the dusty outer arms, there are large portions
of the Milky Way that are obscured from view.
Physical cosmology, as a branch
of astronomy, is the study of the large-scale
structure of the universe and is concerned with
fundamental questions about its formation and
evolution. Astronomers try to measure it all the
time. They use a special instrument called a
spectroscope to tell whether an object is moving
away from Earth or toward Earth. The age of the
Universe can also be estimated from a cosmological
model based on the Hubble constant and the densities
of matter and dark energy. As the early universe
developed the stars were drawn together into large
clusters called galaxies. And hundred billion stars
in our galaxy, hundreds of billions of galaxies in
the observable universe.
Astronomy is one of the oldest
sciences. Astronomers of early civilizations performed
methodical observations of the night sky, and
astronomical artifacts have been found from much earlier
periods.
Saturn is soo far from the
sun that its atmosphere is of course colder than the one
of Jupiter. The temperature above the clouds is minus
170 degrees compared to those of Jupiter being minus 120
degrees. The atmosphere is almost similar comprising
mainly Hydrogen- Helium and also Methane and Ammonia are
present.
Comets originate in the outer solar system; they are thrown
inwards towards the Sun by gravitational perturbations from
planets or nearby stars. They have a variety of different
orbital periods, ranging from a few years, to 50 or 100 years,
to thousands of years, while some are believed to pass through
the inner Solar System only once before being thrown out into
interstellar space. Short-period comets are thought to
originate in the Kuiper Belt, which lies beyond the orbit of
Neptune. Some comets can very occasionally collide with a
planet or satellite. As comets approach the Sun they develop
enormous tails of luminous material that extend for millions
of kilometers from the head.
A telescope is an instrument designed
for the observation of remote objects by the collection of
electromagnetic radiation. The first known practically
functioning telescopes were invented in the Netherlands at
the beginning of the 17th century. "Telescopes" can refer to
a whole range of instruments operating in most regions of
the electromagnetic spectrum.The
Celestron telescope was founded in
the early 1960s by Tom Johnson. Celestron made its name with
the first commercial produced Schmidt-Cassegrain
telescope introducing its "C8" 8-inch
telescope designed by Johnson.
