Science SHS Entrance Exam Reviewer

• Star - A giant ball of hot,

  glowing gases

  (usually hydrogen

  & helium).
• Nuclear Fusion - A process where the nuclei of atoms join and emit energy as light, heat and other electromagnetic radiation.
• Apparent Magnitude Scale - A measurement of

  a celestial object's

  brightness when

  viewed from Earth

  (the more positive

  the number the

  dimmer the star).
• Absolute Magnitude Scale - A measurement of a celèstial object's brightness if viewed from the same distance: a measure of a celestial object's actual brightness or luminosity.
• Hertzs-prung--Russel Diagram (HR) - A graph that plots a star's temperature on the X-axis and absolute magnitude on the y-axis.
• Main Sequence - A diagonal band most stars fall into when plotted on the HR Diagram.
• Speed of Light - Light travels at 300,000 km/s
• Light-Year - The distance that light travels in a year (9,500,000,0- 00,000 km).
• Parsec - Approx. 3.26 light-- years.
• Parallax - The effect where an object appears to move when viewed from twWo different positions.
• Galaxy - A group of stars held together by their gravity, galaxies form three shapes, elliptical, spiral and irregular.
• Constellation - An imaginary picture in the night sky made up of stars.
• Nebula - A cloud of gas and dust held together by the gravity of the hydrogen atoms within it.
• Protostar - When the center of a nebula heats up and pressure increases.
• Hydrostatic Equilibrium - The baiance of the forces of a star's gravity output.
• Red Giant - Hydrogen decreases, gravity is stronger than energy output, a and energy new type of nuclear fusion begins, releasing more energy, reaching a new hydrostatic equili- brium and cooling to red.
• Planetary Nebula - Helium supply decreases in a red giant and the outer region fades to a shell.
• White Dwarf - The core of a planetary nebula Continues nuclear fusion, increases energy rate and temperature to get a small, white hot star.
• Black Dwarf - The result of a white dwarf cooling and fading away.
• Red Superagiant - A continuation of the red giant until iron is formed, resulting in a much larger, red star.
• Supernova - The event where a

  red supergiant

  runs out of energy

  and coliapses.

  resulting in a large

  expiosive death.
• Neutron Star - The aftermath of a

  Supernova with a

  mass of less than

  3 solar masSes, an

  incredibly dense

  star with a

  diameter of only

  tens of kilometers.
• Black Hole - The result of a Supernova with a mass greater than 3 solar masses, a region of space with an extrao- rdinary gravitational pull and density that even light cannot escape.
• Absorption Spectrum - A spectrum with lines missing from the pattern due to elements of the star absorbing their light wavelengths, therefore removing them from the spectrum.