STAR & PLANET IDENTIFICATION

I spotted Pelican Pete going up the mast to check his rigging, 
so I figured that this was a perfect time to ask him a question.

“Pelican Pete!  I've been trying to learn the stars and constellations, 
but it is more boring than trying to learn Morse code.  
Do you have any tips on how to make it easier?”

Pete replied, “Memorizing the stars is like memorizing the exploded 
diagram of your bilge pump in the user's manual. It may come in handy 
on a dark stormy night, but it is more practical to keep a paper copy 
of the manual in a zip-lock baggie, rather than trying to memorize it. 

The same is true of your star chart.  In fact, it is important to learn 
to do star and planet sights without knowing their names.  
In other words, shoot first, then figure out what it was later.  

Sometimes when the conditions are the worst, we may only see  
fleeting glimpses of a body through the cloud cover. If  there is 
a patch of clear horizon below it, then you might be able to get 
a good sight on it.  Under these overcast conditions, you will 
probably not be able to see enough of the constellation to 
identify the star.  In the case of a planet, knowledge of the 
constellations doesn't help much because the planets move through 
the constellations. 

Without knowing the name of the body, you can easily figure it out 
if you took a compass bearing of it, right before or after you get 
the sextant sight.  So in a critical situation, with a heavy cloud 
cover, it is best to just concentrate on getting some good sights, 
with compass bearings and GMT, then identify the bodies later.

To identify stars and planets, NavPak has a Globe View, Sky View, 
and Star Chart. These are helpful to visualize the celestial sphere 
from various different perspectives, but the Star & Planet Identifier 
Panel is the most important identification tool during overcast 
conditions where we can only briefly see a star here and there 
through windows in the clouds.”

Star & Planet Identifier Panel

This panel gives you the Sidereal Hour Angle (SHA) and Declination 
(Dec) of the body based on your Assumed Position, Height Observed, 
GMT, and compass bearing.

The Nautical Almanac gives the SHA and Dec of the planets and hundreds 
of stars.  These values change slowly for the stars, so they are 
tabulated in the back of the book.  For the planets, these values 
change quickly, so they are listed in the Daily Pages.

To use the panel, enter your sight information, which consists of: 
Height of Eye (HE), Height of Sextant (Hs), Assumed Position (AP),  
GMT, compass bearing and magnetic variation.  

Tap [CALC] and it will search through the planets, Selected Stars*,
and Polaris to find a match.  If it does not find a match, then it 
is probably another Tabulated Star**, so you can use the resulting 
SHA and Dec to find a match in the other Tabulated Stars in the back 
of the Nautical Almanac.

Assuming that the info you entered was reasonably accurate, you should
be able to find a match.  If there is a discrepancy in your info, 
it will probably be the compass bearing.  

It is difficult to get a good bearing on a star with a conventional 
hand bearing compass.  I suggest that you get a scope for your sextant 
with a compass in it.  Otherwise try to find a hand bearing compass 
that you can point high in the sky.  Actually, get both.  Under the 
best conditions with the best equipment, your compass bearing probably 
won't be any better than 1 or 2 degrees.  

By comparison of the accuracy, your Hs will be within 1 or 2 minutes,   
so we want to get the bearing as close as possible. If your Hs is off 
more than 2 minutes, then it's garbage anyway, unless it's the only 
sight you have.  Your Assumed Position could also be off by 1 or 2 
degrees. So we want to get the bearing and AP as close as we can.

When NavPak looks for a match, it allows a sloppy tolerance, since 
the Selected Stars are well spread out.  The sum total of your 
discrepancy shows up as a decimal number next to the SHA and Dec.
This can be thought of as a confidence factor.  Anything less than 
1.0 and it is probably a sure bet.  Give it some practice on the 
beach, shooting planets, Selected Stars, and other Tabulated Stars.

If NavPak doesn't find a match, then use the SHA and Dec to find a 
match in the other Tabulated Stars in the back of the Nautical Almanac.

On the Star Chart in NavPak Android/Kindle, the Selected Stars of 
the first magnitude are yellow, Selected Stars of the second magnitude 
are orange, and the other tabulated stars are red.

---------------------------------------------------------------
*  Selected Stars.  These are the 57 brightest stars used for navigation.
** other Tabulated Stars. These can be used for navigation, but normally 
they are too dim to get a good sight.

To be continued...