and What are eclipsing binaries, pulsating stars, and cataclysmic variables? Why are RR Lyrae and Cepheid variables useful in astronomy? What is a "standard candle"?
2007-03-28 11:31:26 · 3 answers · asked by darkvamp4542 3 in Science & Mathematics ➔ Astronomy & Space
A standard candle is an astronomical object (usually a star) which has a known brightness or luminosity. There is a formula that lets one calculate the distance to that object by knowing how bright the object appears to be and how bright is actually is. For example, all incandescent 100 watt bulbs are the roughly the same brightness. Let's say that at 100 feet away the bulb appeared 1/2 as bright as at 10 feet, 500 feet it appeared 1/5 as bright as at 10 feet. If someone pointed to a light across the street and said "Hey that is a 100 watt bulb." You could compare its brightness to your brightness chart for 100 watt bulbs and determine how far away the bulb actually was.
Cepheid variables are used this way. They pulsate, growing brighter and dimmer over time in a constant cycle. There is a relationship between the period of their cycle and how bright they actually are. It is the 100 watt bulb problem all over again. You know how bright they appear to be, and you know (from their cycle) how bright they actually are, so you can calculate their distance. RR Lyrae stars are the same.
Using these standard candle the rough dimensions of our galaxy can be charted. Even the distances to a few close galaxies can be determined this way.
Eclipsing binaries are stars that are so oriented in space that one of them gets directly between us and its companion in exactly the same way that the moon gets between us and our own sun. One star hides the other behind it. Some eclipsing binaries can be used as standard candles, too.
Pulsars are neutron stars that rotate with a very strong electro-magnetic field. The magnetic field focuses the charged particles that are ejected from around the neutron star. This loss of energy causes the star to slow down over time.
HTH
Charles
2007-03-28 13:21:51 · answer #1 · answered by Charles 6 · 0⤊ 0⤋
a pulsar will eventually slow down and cool off and then just be a very dense blackened ball floating around uselessly.
eclipsing binaries are two stars orbitting each other. and whose orbit is in line with earths so that we see them edge on. then they eclipse each other as they orbit, so the stars gets dimmer and brighter.
pulsating stars, any stars that pulse, not to be confused with pulsars, which are totally different.
cataclysmic variables are stars that are so unstable that their variations are chaotic and random. usally these stars are good candidates for supernovae.
cepheids pulse at a certain rate that is dependent on how bright they are. so if you can see a cepheid in another galaxy and measure its pulse rate, then you can figure out how bright it actually is. then using this info you can figure out how far away it is. this makes them a standard candle in calculating how far away galaxies are.
2007-03-28 21:11:05 · answer #2 · answered by Tim C 5 · 0⤊ 0⤋
a pulsar is a rotating neutron star with an EM field, the reason it is called a pulsar is because you can only see the light from the star when the EM poles are pointed directly towards you (or whatever is receiving the frequency) as it rotates. as pulsars age, their rotation slows down, therefore the period that it pulses gets longer
2007-03-28 18:42:29 · answer #3 · answered by Danielle S 2 · 0⤊ 0⤋