Stellar Parallax Magnitude and H-R Diagram

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Presentation transcript:

Stellar Parallax Magnitude and H-R Diagram

Distance to Stars is Measured in: Km – kilometers (#’s become too large to write) AU – Astronomical Unit (the average distance of Earth-Sun 1.5 x 108 (#’s can still become too large) L.Y. – Light Year, the distance light travels in 1 yr. at the speed of 186,000 mi/sec OR 300,000 km/sec Parsec - 3.26 L.Y. ( 1 sec or arc)

Stellar Parallax The shift in the direction of a star caused by the change in the position of the Earth as it moves about the Sun A technique that measures the slight shift in nearby stars to determine their distances. http://sci2.esa.int/interactive/media/flashes/2_1_1.htm

We use trigonometry to calculate the distance to the star (Hypotenuse) Right angle Use the Formula: Sino = opposite hypotenuse Opposite = Earth/Sun Average distance (1 AU) 1.5x 108 km Why is stellar parallax effective for measuring the distance to only the closest stars?

Sample Calculation: Bernard’s Star Sino = 2.69 x 10-6 Formula: Sino = opposite/hypotenuse 2.69 x 10-6 = 1.5 x 108 km X 2.69.10-6 X = 1.5 x 108 2.69 x 10-6 2.69 x 10-6 X = .55 x 1014 Km (5.5 x 1013)

The farther away the star the smaller the angle of parallax becomes The farther away the star the smaller the angle of parallax becomes. Eventually the angle will become so small we are unable to measure it

Absolute Magnitude and Apparent Magnitude

Magnitude – The brightness of a star Apparent Magnitude The brightness as we see it from Earth Absolute Magnitude The actual brightness of a star when compared to other stars at a standard distance of 10 parsecs. (32.6 L.Y.s) Luminosity - the total amt. of energy a star is sending out. This is independent of how far away the star is. The greater the luminosity the greater the absolute magnitude.

Stars must be compared at 10 parsecs Compare the two stars below. If Sirius appears very bright to us What is the distance for Sirius, 2.6 pc or 5 pc?

The scale for measuring magnitude is based on the larger the # the less bright!! The Sun - very bright at -26 Polaris – less bright at +2

What factors determine the Magnitude? Size Temperature Distance

Comparing Luminosity to Absolute Magnitude Luminosity – the amt. of energy released by star Magnitude – the brightness of a star SUN -> The Sun has a luminosity of 1. A luminosity of 10,000 means The star is 10,000 times more Energy than the Sun.

Compare the magnitudes. Is star’s distance close? Far away? Star Apparent Magnitude Absolute Magnitude distance The Sun -26.93 4.8 ? Sirius -1.44 1.41 Vega 0.03 0.58 Betelgeus 0.45 -5.14 GJ 75 5.63 Star Apparent Magnitude Absolute Magnitude distance The Sun -26.93 4.8 ? Sirius -1.44 1.41 Vega 0.03 0.58 Betelgeus 0.45 -5.14 GJ 75 5.63 Complete the practice sheet **Magnitude Questions