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Latest Threads
Sighting the eclipse
Forum: General Topics Here
Last Post: BigBill
Today, 04:31 AM
» Replies: 4
» Views: 17
About the August 21 Solar...
Forum: The August 21 Total Solar Eclipse
Last Post: CelNav57
08-20-2017, 12:57 AM
» Replies: 0
» Views: 7
How to buy a sextant
Forum: General Topics Here
Last Post: BigBill
08-13-2017, 11:16 PM
» Replies: 8
» Views: 251
Electronic Sextant G-Stel...
Forum: General Topics Here
Last Post: LouisC
07-12-2017, 11:18 AM
» Replies: 3
» Views: 297
Planning for twilight phe...
Forum: The Sight Reduction process
Last Post: Rumata
07-04-2017, 06:48 AM
» Replies: 5
» Views: 156
Doesn't matter which row ...
Forum: The Sight Reduction process
Last Post: Rdutton
06-13-2017, 10:29 AM
» Replies: 2
» Views: 197
This is a great resource
Forum: General Topics Here
Last Post: CarlosPindle
06-02-2017, 04:51 PM
» Replies: 1
» Views: 427
Why Polaris isn't listed?
Forum: The Sight Reduction process
Last Post: CelNav57
05-05-2017, 02:01 AM
» Replies: 14
» Views: 624
Great Circle route diffic...
Forum: General Topics Here
Last Post: BigBill
04-28-2017, 04:11 PM
» Replies: 4
» Views: 466
2017- Compact version- Th...
Forum: 2017- Everything you need
Last Post: CelNav57
04-21-2017, 01:28 AM
» Replies: 3
» Views: 748

 
  Sighting the eclipse
Posted by: BigBill - Yesterday, 03:37 PM - Forum: General Topics Here - Replies (4)

I'm thinking I might try and take a sextant sighting of the sun (and moon) during the eclipse. It could be interesting.
I hope the clouds stay out of the way.

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  About the August 21 Solar Eclipse
Posted by: CelNav57 - 08-20-2017, 12:57 AM - Forum: The August 21 Total Solar Eclipse - No Replies

You can find everything you need to know about the solar eclipse on Monday, August 21, 2017 here-

A map and demonstration of the August 21, 2017 total Solar eclipse.

More information can be found here-  August 21 Solar Eclipse

It will be viewable in these world areas;

Hawaii

N.E. Pacific Ocean

North America

Central America

northern parts of South
America

westernmost tip of Europe and
W. Africa.



Here's hoping for Clear Skies!

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  How to buy a sextant
Posted by: james1979 - 08-01-2017, 08:25 PM - Forum: General Topics Here - Replies (8)

Dear all,
I have been starting to consider some options to buy a sextant, and I have seen that many buy sextants that a no longer produced, or 'vintage' sextants, see for example this thread. Given that sextants are highly delicate precision instruments, how do you guys make sure that you will get a sextant in proper conditions when you buy a 'vintage' one? Is there a way to identify reliable online vendors? 

For example, in the thread above Douglas Denny says:

Quote:I have various sextants but the 'best' of all was amazingly cheap costing about £200  ($240  exchange rate Jan 2016), bought about four or five years ago;  it is a Russian SNO-T and was new, unused in the original box.  These were ex-Russian Navy released presumably as surplus to requirements.


Given that this is a 'vintage' model, I wonder how one could make sure that it was new in the box before purchasing it. 

Finally, I have a question about brand new sextants. I see that the brand that makes the sextant is not the same as the distributor. For example, Tamaya Technics does not sell directly its sextants. To buy one, one may go to Celestaire, or other distributors. What are some good, reliable distributors in Europe? Is Celestaire one of these? 

Thank you for your help!

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  Electronic Sextant G-Stell
Posted by: CelNav57 - 07-08-2017, 11:01 PM - Forum: General Topics Here - Replies (3)

A French company has invented an electronic sextant and named it G-Stell.

Here's a link to it.

G-Stell electronic sextant

I found it while looking at links related to an upcoming boat show in France (Cannes?).  However, I have not seen that there is actual production of the G-Stell or price and availability.

It looks very promising.

CelNav57

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  Planning for twilight phenomena observation
Posted by: CelNav57 - 07-02-2017, 01:17 AM - Forum: The Sight Reduction process - Replies (5)

Rumata had posted this question on another thread but I've moved and made a specific thread for his question as follows;



Gentlemen, I have a question regarding planning for twilight phenomena observation. But before some wordy stuff, sorry.

The situation: In a morning I plan for sunset phenomena observation.  I understand that below is the way to do it.:

1.  From NA find LMT for sunset, civil and nautical based on the  MOST RECENT FIX OR DR LATITUDE. ( emphasize by caps).
2. Find GMT by converting most recent fix or DR longitude into time and add/subtract it to LMT
3. Find from NA GHA of Aries for this GMT and calculate LHA of Aries
4. Pub.249 gives a list of stars as a function of LHA Aries and latitude OF THE MOST RECENT FIX OR DR.

i think that more correct approach would be:

1. Calculate assumed distance travelled considering time of civil twilight as the time of a new DR ( v* (time of last fix/DR - time of civil twilight).
2. Plot it and find latitude and longitude at the new assumed DR.
3. Using these latitude and longitude do items 1-4 from the paragraph above.

I suppose that in this case latitude and longitude would really correspond to the twilight phenomena and to LHA Aries than the values taken at the current location, presumably 10 hours earlier.

There is my question: does my guess make some sense?

Thank you

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  This is a great resource
Posted by: BigBill - 06-02-2017, 02:59 PM - Forum: General Topics Here - Replies (1)

Despite the lack of activity in the forums, I wanted to express my appreciation for everything here. I use the almanac regularly and have learned a lot from the information presented.

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  Doesn't matter which row or column in Table 5?
Posted by: EdCa - 05-16-2017, 01:29 AM - Forum: The Sight Reduction process - Replies (2)

Here's and odd question- does it matter whether you use the column for minutes of declination or "d" correction from Pub. No. 249 to get the proper "d" correction?  By this I mean I've discovered that whether 249 specifies any "d" correction (45 for example) and the Sun's declination for a certain day and time (let's just say 21 minutes of declination) the same correction value of 16 can be found whether you use 45 minutes of declination and a "d" of 21 or 21 minutes of declination and a "d" value of 45.  No matter which way you  arrange it you still get a d correction of 16.

That would let me think that Table 5 is goof proof- you'll still get the same d correction value.

What do you think?

Thanks,

Ed


TABLE 5- Correction to Tabulated Altitude for Minutes of Declination

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  Great Circle route difficulty
Posted by: BigBill - 04-22-2017, 08:22 PM - Forum: General Topics Here - Replies (4)

I was brushing up on the procedure for figuring the great circle route, the one in the 50 year almanac by Kolbe and had some troubles. Maybe  I was just tired and the tv was on but 2 attempts at fairly close destinations, both under 400 NM just didn't work. Once I chose someplace more distant, about 2900 NM it worked fine. Is it possible to be too close to use? TIA

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  Why Polaris isn't listed?
Posted by: Rumata - 04-20-2017, 06:14 AM - Forum: The Sight Reduction process - Replies (14)

Greetings, 

I tried to to use intercept method in solving some problems from a book and found out that despite the fact that Polaris is one of the most easily recognizable stars in the Northern Hemisphere Nautical Almanach of 2005 and earlier versions did not have SHA for it. Now, 2017 they do.  So, my question is, why Polaris wasn't included in the list of observable stars in Pub.249 and NAutical Almanacs and is it any way to guess it SHA without jeopardasing the accuracy of plotting too much?

I wanted to place the question as the new one but am not  not sure how to do it.  So I just place it in Sight Reduction forum.

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  Bad Map Might Be Why Earhart Didn't Reach Island
Posted by: P.Rutherford - 04-13-2017, 09:06 PM - Forum: General Topics Here - No Replies

Amelia Earhart and Fred Noonan disappeared into the Pacific ocean in 1937, 80 years ago, and there are still people trying to figure out what happened to them and why.

The story below, click on it, explains that a government chart they used listed Howland island 7 miles Northwest of its actual location. 

Amelia Earhart- inaccurate chart?

It has been often said, "you must be blind not to see an island 2 miles long from an airplane about 1,000 feet off the water".  Consider this- they were flying, upon approach, into the Sun and then turned to follow an LOP on what they thought was passing through Howland- 157° - 337°.  I assume they flew the line in both of those directions looking for Howland.

Now then, here's a picture of Howland- how well can you see it?  I can't see it very well and would assume its the shadow of a cloud cast on the ocean.  Combine those circumstances with the longevity of the length of the flight- they must've been very tired.

[Image: serveimage?url=http%3A%2F%2Ft0.gstatic.c...che=496253]



Paul

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