Flashcards in D.1 Stellar Quantities Deck (16):
What is the solar system?
Consists of eight planets that revolved around the sun. The order of the planted starting form closest to the sun is mercury, menus, earth, mars, Jupiter, Saturn, urns and Neptune. All of these except the first two have moon orbiting them.
What is an asteroid?
Small rocky objects in orbit around the sun between mars and Jupiter.
What is a comet?
A small object of ice, rock and frozen gases whose nucleus is about 10km across. Those comets that orbit the sun have very large elliptical orbits, when a comet is near the sun gases stream out form it for thousands of km in a direction away from the sun.
What is the astronomical distances?
The average distance between the earth and the sun is called an astronomical unit. The distance traveled in one years is called a light year. Another unit is the parsec.
What is a star?
Large mass consisting mostly of hydrogen with temperature in its core that is high enough for nuclear fusion reactions to take place. The energy released in these reactions produces an outward pressure on the outer layers of the star thus preventing gravity from collapsing the star. A star is in equilibrium under the action of the opposing pressures of gravity and radiation.
What is a binary star?
A pair of stars orbiting a common centre. The stars have a common period of revolution which means they are always diametrically opposite each other. The common period is determined by the separation of the stars and their total mass the heavier star is in the inner orbit.
What is a stellar cluster?
A large number of stars relatively close to each other the affect each other through their gravitational forces. Stellar clusters are divided into globular and open cluster. Stars in globular clusters tend to be closest o one another and are many old evolved star, open clusters contain young stars further apart than those in globular clusters.
What is a constellation?
A group os stars in a recognisable pattern as seen from earth, thought not necessarily close to each other in space.
What is a nebula?
A cloud of gases and dust extending for light years across space. It is formed by the mass ejected when a red giant or supergiant explodes.
What is a galaxy?
A collection of very many stars that attract one another gravitationally. A galaxy can be spherical, elliptical, spiral or irregular in shape. The average separation of stars in a galaxy is of the order of a few pc, and the average separation of galaxies is of the order of a few hundred kpc.
What are clusters and superclusters of galaxies?
Galaxies are often found in groups called clusters, and clusters are grouped together in superclusters.
What is luminosity?
The total power radiated by a star given by
L = @AT^4 where A is the stars surface area and T is its surface temperature in kelvin. The @ constant is the Stefan Boltzmann constant, the unit of luminosity is the watt.
What is apparent brightness?
The power received per unit area, a measure of how bright a star appear from earth. It is given by b = L/(4pid^2) where d is the distance to the star from the earth, The unit of apparent brightness is Wm-2. A star with low luminosity may appear brighter than another star of higher luminosity because it is closer.
What is the proton proton cycle?
Hydrogen fuses with hydrogen to produce helium. The outflow of energy from fusion reactions in the core of a star produces an outward radiation pressure that balances the gravitational pressure.
what is the parallax method?
Consists of observing a star at two different times six months apart. In the six months the earth has moved in its orbit around the sun and so the star will be observed to have shifted relative to the background of the very distant stars.