Stellar Distances

Stellar Distances Brittany Griner

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

Radar Ranging

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

Stellar Parallax

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

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

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

Variable Stars

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