* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Apparent Magnitude
Survey
Document related concepts
Dyson sphere wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Corona Borealis wikipedia , lookup
Star of Bethlehem wikipedia , lookup
Stellar kinematics wikipedia , lookup
Aries (constellation) wikipedia , lookup
Stellar evolution wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Canis Minor wikipedia , lookup
Star catalogue wikipedia , lookup
Canis Major wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Corona Australis wikipedia , lookup
Star formation wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Transcript
Ch 28 Apparent Magnitudes In 125 B.C., a famous astronomer of that time, named Hipparchus, was making a star map of the “celestial sphere”. Hipparchus not only wanted to locate each star’s position on his map, but also to indicate the brightness of each star. To do this Hipparchus invented the concept of stellar magnitude. Hipparchus designated the brightest stars as stars of the first magnitude. The dimmest stars visible he designated sixth magnitude stars. The other stars were given magnitudes from second through fifth. Notice the brighter the star, the lower the actual number of the magnitude. The symbol for apparent magnitude is a lower case m. Hipparchus’ system was used until the late 1700’s when it became possible to more accurately measure stellar magnitudes. William Herschel modified the system into essentially the system we use today. Herschel determined the difference in brightness between each magnitude is equal to 5√100 or 2.512. For the purpose of our calculations, we will use the approximation of 2.5. We can therefore produce the following table. Table 1 Difference in Magnitudes 1 = 2 = 3 = 4 = 5 = (2.5)1 (2.5)2 (2.5)3 (2.5)4 (2.5)5 Difference in Brightness = 2.5 = 6.25 = 16 = 40 = 100 Example 1 If one star is a first magnitude star and the other is a third magnitude star, what is the difference in brightness? Answer We first find the difference in magnitude between the two stars (3-1=2). Then we look for the number 2 in the left hand column in Table 1. Now read horizontally across to the right hand column. The answer is 6.25 times difference in brightness. Problems 1a. Star A has a magnitude (m) of 1; Star B has a magnitude (m) of 4. Using Table 1, what is the difference in brightness between the two stars? 1b. Which is the brighter star? 2a. Star A has a magnitude (m) of 2, star B has a magnitude (m) of 6. What is the difference in brightness between the two stars? 2b. Which is the brighter star? Remember that the brighter the star, the lower the magnitude, and that the average of the 20 brightest stars is magnitude 1. Since some of these stars are brighter than the average of their group, a few stars have magnitude lower than 1, and in fact, lower than zero (ex. Negative #’s) Example What is the difference in brightness between a m +2 star and a m or –1 star? Answer The difference in magnitude is three (+2-(-1)=3). Therefore, the difference in brightness (using Table 1) is 16. Also, the star with m= -1 is the brighter star. Problems 3a. Star A has a m of 4, star B has a m= -1. What is the difference in brightness between the two stars? 3b. Which star is the brighter star?