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B Does Modern Astronomy have a problem?

  1. Nov 6, 2017 #21


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    It wasn't clear from the sentence structure what the parenthetical was referencing, and since 18.5 is close to the first three significant digits of the speed of light in miles per hour, I assumed it was referring to the speed of light and in error. But, your reading does make sense.
  2. Nov 6, 2017 #22


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    Is stellar abberation due to Earth's orbital speed actually relevant for parallax measurements? I would have imagined that measurements of parallax would be done by measuring deflection of the target object against a backdrop of other distant objects in photos taken 6 months apart. Stellar abberation from the Earth's motion would cancel out of such a measurement.
  3. Nov 6, 2017 #23


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    It depends on where your reference is and how you establish these references. Gaia for example has the near-term reference by the same telescope and one 60 degrees ahead/behind by the other telescope, and it has to correct for aberration with high precision.

    10-6 speed corresponds to up to 0.2 arcseconds deviation, and Gaia aims for ~10 microarcseconds precision for the brightest stars, a factor 20,000 smaller.
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