"Jim" wrote:
On Apr 6, 11:26 am, (Eugene Griessel) wrote:
"John Nagelson" wrote:
Already downloaded this and printed it - very nice chart
but shows the 57 with names and numbers, not the 173.
I'm sure your life must be empty not knowing that the likes of Eta
Virginis, Delta Velorum and Beta Corvi and the like are also on rare
occasions used to navigate by. I could give the full list but really
think its pointless.
Eugene L Griessel
We do precision guesswork.
173 sounds like too much information - I mean how many are needed to
sucessfully navigae with? Do you really need the 173? Do you need the
57 in total to navigate?
When one navigates by the stars, using a normal marine sextant, the
only time one can shoot the stars is during twilight as both the
horizon and the stars must be visible. So morning and evening
twilight are the only times (barring on odd occasions when the moon is
bright enough to see the horizon). Thus the stars need to be bright.
I doubt many celestial navigators, that is the marine kind, have ever
used all 57 the almanac routinely lists on the daily pages. One needs
three bright stars to get a position. If one is neurotic (like me)
you shoot an extra one or two just to make sure that the position has
not been bedevilled by bad time, bad measurement, bad calculation etc.
My method is to see which bright stars will be visible during twilight
from my ded reckoning postion (using the almanac) - choosing the
brightest and which will give me good angles of cut and figuring out
their estimated azimuth and elevation. So before I even get the
sextant out I know which directions and elevations I will be looking
in. Usually the only bright star there will be the one I want to use.
Chuck in the odd planet, the moon if it obliges well, and I'm away.
I've always maintained that learning how to find about 16 stars in the
hemisphere you are in will do you admirably. I mean I can look up and
identify (say) Castor and Pollux, Betelgeuse, Rigel, Procyon, Sirius,
Capella, Aldebaran, Saiph, Rigel Kentaurus, Alpha Crux, Acnernar,
Canopus and Fomalhaut with 100% certainty. What more do I need -
unless things are really badly overcast - and then celestial becomes
truly iffy anyway. Either the horizon or the star you want will be
obscured. I remember taking a nothern hemisphere aviator on his first
night in the south to show him the crux and being so bedevilled that
no more than two stars of it or the pointers were ever visible at one
time. Big disappointment for him! Next night he saw them all.
BTW - I think the Flamsteed numbers only go as high as 137 - not 173.
May be wrong, should check,
Eugene L Griessel
A free society is one where it is safe to be unpopular.