Particle Accelerators
A huge device
used by particle physicists to accelerate particles. By accelerating particles, scientists
can better understand particle interactions.
Particle Physics
The study of
elementary particle interactions. Particle physicists
historically have worked at particle accelerators.
Recently particle physicists have worked with astrophysicists
to try to understand stars and other stellar objects.
Photons
Particles which are packets
of light. Photons move at the speed of light, 300,000,000 meters per second.
Planets
Large bodies that orbit around stars. There
are nine planets in our solar system. Planets are categorized
into two types: gas giant planets, and
terrestrial planets.
Planetary Nebula
A type of nebula caused by an expanding cloud of gas
ejected by a dying star. For cool pictures, check out HST's
planetary nebula gallery.
Hourglass Planetary Nebula
Pluto
The smallest planet in our solar system. Pluto is
neither a gas giant planet, nor a
terrestrial planet, but rather is though to have been
gravitationally captured by our Sun.
Check out SEDS'
Nine Planets, for more
about planets. Or see StarDate's
Solar
System Guide.
Polaris
The proper name of the north star.
Protons
A sub-atomic particle found
in the nuclei of an atom. The proton
has a positive charge.
Quasar
A Compact, extra-galactic object which emits
huge amounts of energy, but looks like a point of light. Black holes are thought to live at the
center of quasars. Several thousand quasars are known. Quasar is actually short for
quasi-stellar object (QSO).
Quarks
A type of sub-atomic particle,
quarks are thought to be the most elementary of particles.
Right Ascension (R.A.)
A coordinate used on
the celestial sphere just as longitude is used on Earth.
An object's right ascension is measured in hours and minutes eastward from the vernal equinox.
Saturn
Saturn has an orbit of almost 1.5 billion km.
It is the second biggest planet and is a gas giant planet.
Check out SEDS' Nine
Planets, for more about planets. Or see StarDate's
Solar System Guide.
Saturn
Solar System
Any system composed of one or more
stars and one or more planets or other celestial bodies gravitationally bound to the star(s).
Although most solar systems are binaries (meaning that they have two stars), our own solar
system is composed of one star (named Sol, but commonly called the Sun), nine planets, and
other, smaller stuff. Since 99% of the mass in the solar system is in the Sun and Jupiter,
astrophysicists like to joke that our solar system is composed of the Sun, Jupiter, and other
stuff. This probably says more about astrophysicists than it does about our solar system.
Sidereal Day
The period of rotation of an object
with respect to the stars. Compare this to a solar day, which is the period of rotation of
an object with respect to the Sun. On Earth a sidereal day is 23 hours, 56 minutes and 4
seconds, while the solar day is 24 hours.
Spiral Galaxy
A class of galaxy, spiral galaxies
are so named because of their spiral shape.
Spiral Galaxy
Standard Candle
A type of object whose brightness
is well understood. Standard candles are used to determine how far away distant objects are.
Cephied variables and supernovae
are used as standard candles.
Standard Time
The time in Greenwich, England,
used by scientists by synchronize events. Standard Time is also called Universal Time and
Greenwich Mean Time.
Summer Solstice
The point on the
ecliptic where the Sun is farthest north. The summer solstice,
which is the longest day of the year, occurs on, or near, June 21, and marks the beginning of summer.
See celestial sphere for a helpful diagram.
Sun (Sol)
Big yellow thing visible in the sky during the
day, the Sun is by far the largest object in the solar system. It has a
mass of 2,000,000,000,000,000,000,000,000,000 kg. It has a diameter of almost
1.4 million km. Over 100,000 Earths could fit inside the Sun! The Sun is composed mostly of
hydrogen, and is about five billion years old. Check out SEDS'
Nine Planets, for more
about the Sun. Or see StarDate's
Solar System
Guide.
Supernova
The explosion resulting when a massive star
explodes violently, becoming temporarily brighter than a thousand stars. Because supernovae
are so bright, they can be seen from very far away, and thus are useful as
standard candles. For more about supernovae, check out the
distant supernova search.
Terrestrial planets A type of planet characterized by having a rocky core, and by being small and close to the Sun. Mercury, Venus, Earth and Mars are terrestrial planets.