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

Answer 1

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

  1. It is about #40 \quad pc# for ground based observations.
  2. 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#
  3. 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#
  4. 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 # 50 \quad kpc# and #64\quad kpc# come inside the resolution of GAIA. But the Andromeda galaxy our nearest neighbour after these dwarf galaxies lie at a distance of #778\quad kpc# which lies well outside GAIA's capacity to probe.

    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.

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Answer 2

Because galaxies are so far away—much farther away than the stars for which trigonometric parallax works—we are unable to calculate the distances to them using trigonometric parallax because the angular shift in position caused by Earth's orbit around the Sun is too small to measure for galaxies. Instead, astronomers use techniques such as standard candles, redshift, and the cosmic distance ladder to estimate distances to galaxies.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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