CHARACTERISTICS OF STARS
LEARNING GOALS I will be able to explain the colour, mass, and temperature of a star. I will be able to distinguish between absolute and apparent magnitude.
STAR BRIGHTNESS Luminosity: amount of energy produced each second by a star. Luminosity is measured by comparing a star to the luminosity of our sun (luminosity = 1) The brightest star in the night sky, Sirius, has a luminosity = 22. Sirius
Luminosity is also affected by the distance each source is from the observer. Sirius is 22 times brighter than the sun and yet, the sun appears brighter. Why? Sirius is 9 ly away and the sun is 1.6 x ly away When placed at equal distances from the observer, the light with higher luminosity will appear brighter.
APPARENT & ABSOLUTE MAGNITUDE Apparent Magnitude: The brightness of stars in the night sky as they appear from Earth. Lower magnitude = brighter celestial objects. i.e Sun >> Apparent magnitude = -27; vs. Polaris >> Apparent magnitude = 1.97 Absolute Magnitude: The brightness of stars as if they were all located 33 ly from Earth. I.e: Sun >> Absolute magnitude = 4.8 vs. Polaris >> Absolute magnitude = -3.63
Therefore, if Polaris and the Sun were side by side, Polaris would appear much brighter. Which of these five stars is the brightest from Earth? From an equal distance away? From Earth: The Sun, apparent magnitude From equal distance: Deneb, abs. magnitude -7.5 StarApparent MagnitudeAbsolute Magnitude Sun Sirius Vega Betelgeuse Deneb
STAR COLOR & TEMPERATURE Color of a star gives scientists an indication of the surface temperature. Hottest stars appear bluish-white whereas cooler stars appear reddish Our sun, with a temperature of C and a yellowish-white appearance falls midway in the table. Blue star Rigel
COLOR AND TEMPERATURE RANGES OF SOME STARS ColorTemperature Range ( 0 C) Example(s) Bluish25000 – 50000Zeta Orionis Bluish-white11000 – 25000Rigel Whitish7500 – 11000Sirius Yellowish-white Polaris Yellowish Sun Orangish Arcturus Reddish Betelgeuse Zeta Orionis in Horsehead Nebula
THE MASS OF A STAR The mass of our sun is 2 x kg and is referred to as one solar mass. Scientists use this measurement to compare masses of other stars. These masses can range from 0.1 to 120 solar masses. i.e. AI (a massive star) has a solar mass of 118!
LEARNING GOALS REVISISTED I will be able to explain the colour, mass, and temperature of a star. I will be able to distinguish between absolute and apparent magnitude.
YOUR TURN … Please complete p373 #7, 8, 10, 11