Distance of Stars

1. Trigonometric parallaxes

2. Parallax decreases with distance

3. Parallax formula

d=1/p

p = parallax angle in arcseconds

d = distance in "Parsecs"

3.1.Parallax Second = Parsec (pc)

A star with a parallax of 1 arcsecond has a distance of 1 Parsec.

1 parsec (pc) is equivalent to:

206,265 AU

3.26 Light Years

3.086x10¹³km

4. Light year

1 Light Year is the distance traveled by light in one year.

1 light year (ly) is equivalent to:

0.31 pc

63,270 AU

5. Hipparcos

The Hipparcos satellite (launched by the European Space Agency in 1989) measured precision parallaxes to an accuracy of about 0.001-arcsec.

Hipparcos measured parallaxes for about 100,000 stars

Got 10% accuracy distances out to about 100 pc

Good distances for bright stars out to 1000 pc.

6. Gaia

Gaia is a European follow-up mission to Hipparcos that was launched on 19 December 2013, reaching its orbital station at the Earth/Sun L2 point in January 2014, and began science operations in July 2014. Its goal is to conduct what amounts to a Galactic census. Gaia is undertaking an all-sky survey of the Galaxy that build up high-precision angular measurements through repeated measurements. The final Gaia data catalog will not be completed until about 2020.

Mission Goals:

Measure positions and motions for about 1 Billion Stars

Measure parallaxes for >200 Million Stars

Max precision of 10 microarcseconds

This means 10% or better distances out to 10,000pc