# Why can’t we determine the distances to galaxies using the geometric method of trigonometric parallax ?

##### 1 Answer

Mar 9, 2016

There is a limit in using parallax method to find stellar distance.

#### Explanation:

- It is about
#40 \quad pc# for ground based observations. **Hipparcos**: In 1989 ESA launched Hipparcos (HIgh Precision PARallax COllection Satellite) which could measure parallaxes as small as#1 \quad# milli-arc seconds which translate to a distance of#1000\quad pc = 1 \quad kpc# **GAIA**: In 2013 ESA launched the GAIA satellite, a successor to Hipparcos which can measure parallaxes as small as#10\quad# micro arc-seconds which translate to a distance of#10^5\quad pc = 100 \quad kPc# **SIM**: NASA had its own Space Interferometry Mission (SIM) which planned to measure parallaxes as small as#4\quad# micro src-seconds which translates to a distance of#250\quad kpc# . But the mission had been finally cancelled.

The **LMC** and **SMC** dwarf galaxy systems (Large Magellenic Cloud and Small Magellenic Cloud) at distances of approximately

When distance increase the Angle become very small and is difficult to measure..In such case a Cepheid variable is used as standard candle to measure distances.

picture credit astronomy ohio state ed.