Download PSC100 Transparant Replacement for Chapter 8 Measurement of

Measuring the Distance to Stars
Measuring Method
Max. distance
8-2a
Accuracy
Radar
1/1000 Parsec
** Finds distance to the planets and the Sun
.01%
Stellar Parallax
20 - 40 Parsecs
** Finds distance to nearest stars in Milky Way
10%
Spectroscopic Parallax
100 Parsecs
** Finds distance to far away stars in our galaxy.
15%
Standard Candle Methods
Similar spectra class stars
** Finds distance to nearby galaxies
20%
Variable stars
** Finds distance to most distant galaxies
25%
5th brightest galaxy
50%
Supernova / Nova explosions
50%
Measuring the distance to stars is so important that many
astronomers spend their entire lives working on this.
Even though it is critical to understanding many of the other
properties of stars, we can only determine the distance to far away
objects in space to about 50% accuracy.
8-2 b
How do these methods of measuring distance work?
Radar
* Send out radio signal toward object in our Solar system.
* Measure time for reflected signal to return to Earth.
* Calculate distance as speed of light x time of travel.
Stellar Parallax
* Measure angle to star at two different times.
* Use largest base line possible, the diameter of Earth’s
orbit around the Sun
* This means data readings must be taken 6 months apart.
* Calculate distance using triangulation.
Spectroscopic Parallax
* Once a star is plotted on an H-R diagram, its distance
can be found on the other coordinate axis.
Standard Candle Methods
* Determine two light sources are similar in brightness.
Similar spectra class should mean that the two stars
have about the same intrinsic brightness.
Variable stars have flash rates that tell their luminosity.
5th brightest galaxy in any cluster assumed to have
about the same absolute magnitude.
Supernova explosions all assumed to have about the
same total energy output.
* Use the inverse square law of brightness as a function
of distance to compare the visual magnitude as seen
from Earth to the absolute magnitude..