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Why do they always track Canopus?

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#1 Araguaia

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Posted 25 January 2020 - 03:49 AM

Navigation systems in most spacecraft seem to have a Canopus tracker.  

 

Not brighter Sirius - perhaps because Sirius will occasionally be too close to the Sun.  But then wouldn't something like Alpha Centauri be even better, being at a wider angle to the plane of the Solar System?



#2 Redbetter

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Posted 25 January 2020 - 04:06 AM

Compared to Alpha Centauri, Canopus has several advantages I suppose:

  • Far, far more distant, so less parallax.
  • Far, far smaller proper motion so less year to year change in position.
  • It isn't part of a nearby multiple star system--the orbit again adding to complexity of position determination.

Based on the above, if I was going to pick something bright for precise alignment in orbit I wouldn't pick Alpha Centauri.



#3 Tony Flanders

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Posted 25 January 2020 - 06:35 AM

Canopus is the bright star that is closest to the South Ecliptic Pole. Or to put it as you did, it's farthest from the plane of the solar system. Alpha Cen is about 45 degrees from the ecliptic; Canopus is about 75 degrees from the ecliptic.


Edited by Tony Flanders, 25 January 2020 - 06:39 AM.

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