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Stellar Distances

Stellar Distances . Brittany Griner. Radar Ranging . When a light signal is directed at a nearby planetary body part of the signal will be reflected back By timing how long it takes this light echo to return, the distance to the planet can be determined

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Stellar Distances

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  1. Stellar Distances Brittany Griner

  2. Radar Ranging • When a light signal is directed at a nearby planetary body part of the signal will be reflected back • By timing how long it takes this light echo to return, the distance to the planet can be determined • The atmosphere poses difficulties and this is one reason that radio waves are used as the atmosphere is largely transparent to certain radio frequencies • The second difficulty is signal strength • The signal will start to spread out as soon as it is sent

  3. Stellar Parallax Stellar parallax the difference in direction of a celestial object as seen by an observer from two widely separated points The measurement of parallax is used directly to find the distance of the body from the Earth and from the Sun The two positions of the observer and the position of the object form a triangle

  4. Spectroscopic Parallax 1. Take spectra of a star 2. Types of spectral lines ⇒ spectral class ⇒ horizontal position 3. Thickness of spectral lines ⇒ luminosity class 4. Location on HR Diagram ⇒ absolute magnitude 5. Distance Modulus ⇒ distance The spectroscopic parallax technique requires that a star's apparent magnitude and its spectrum have been observed Information gathered from the spectrum is used to find the star's position on the HR Diagram The types of spectral lines in the star's spectrum allow astronomers to determine the spectral type which determines the location of the star horizontally on the HR Diagram

  5. Variable Stars • Is a star whose brightness as seen from Earth fluctuates • This variation may be caused by a change in emitted light or by something partly blocking the light • Variable Stars are classified as either: • Intrinsic variables, whose luminosity actually changes • Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth

  6. http://astro.unl.edu/naap/distance/radar.html http://abyss.uoregon.edu/~js/glossary/parallax.html http://astro.unl.edu/naap/distance/spectroscopic_parallax.html

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