Glossary

Glossary: P through T

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

P

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.

Q

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.

R

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.

S

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.

To find out what the Universal time is click here. Warning! This can be slow!

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.

T

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.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Last modified: 1/15/1998, by Paul Shestople
Questions or Comments?
Contact: cfpaedu@physics.berkeley.edu