What is the Magnitude Scale?
A magnitude scale is a numerical tool of reference, most often used to describe either the strength of an earthquake or the brightness of a star as seen from earth. The scale that is most commonly used to denote the brightness of stars, or their “apparent magnitude,” is called the astronomical magnitude scale. For the description of earthquakes, the Richter scale and the moment magnitude scale are used. The astronomical magnitude scale defines the magnitude of stars based on the amount of light they give off as perceived by an observer on earth. The higher a star’s magnitude number, the dimmer it appears. For example, the brightness of the sun, our closest star, is about a magnitude -26, while the full moon is assigned a magnitude of about -13. An observer in an urban area will be able to see some stars at night, but none dimmer than a magnitude three. Someone in a rural area can see stars as dim as magnitude six or seven, and binoculars bring the number almost to ten. Telescopes allow
This image was copied from Nick Strobel’s Astronomy Notes. The magnitude scale is a logarithmic scale in which each integral step corresponds to a change of approximately 2.5 times in brightness. Brighter objects have smaller magnitudes than dimmer ones. For example, an object with magnitude m = 1 is about 2.5 times fainter than an object with magnitude m = 0. The magnitude scale originated with the Greeks, who designated the brightest stars in the sky as “first magnitude” and the faintest stars that the eye can see as “sixth magnitude.” (The Greeks hadn’t yet learned about the number “0!”) Astronomers later quantified the magnitude scale, and extended it to brighter and fainter stars. With binoculars or a small telescope, you can see stars as faint as about 10th magnitude, and the Hubble Space Telescope can detect stars as faint as 30th magnitude, about 10 billion times fainter than the eye can see. The magnitude of a star depends on two factors, the intrinsic brightness of the star a
How are brighter stars denoted? 2) What are Keplers three laws of motion? 3) How does the gravitational pull between 2 objects change if the objects masses or distance change? 4) What is the difference between mass and weight? 5) List several applications of Einsteins Special Theory of Relativity. Repeat for the General Theory of Relativity. 6) What are the various parts of the electromagnetic spectrum? How do these parts vary in wavelength? 7) What is Placks law? 8) What is reflection? Refraction? 9) What are the basic parts of a refractor? A reflector? 10) Describe the three powers of a telescope. What does each depend on? Which is the most important power? 11) What is the difference between a Newtonian and Cassegrain reflector? 12) What are some of the problems with refractors? With reflectors? 13) What is the problem with the HST? 14) List Kirchhoffs rules of spectra 15) How is a stars color related to its surface temperature? 16) List the Harvard spectral classes from hot to cool.
