Wednesday, January 30, 2013

The star clock

The World Cruising Club stand at the Boat Show had a short talk by Stokey Woodall on navigating by the stars, and having fond memories of the night's sky mid Atlantic boosted by reading Tristan's book on Natural Navigation, I went along for a prep.

Most of it was based upon spotting Polaris but there was one nice trick about how to use it and the Plough to work out your time.

Basically look at the night's sky and think of a back to front clock as in the graphic above, and then work out the "sky hour" of the leading edge of the Plough.

Then the time can be estimated using:
       Time = 41.5 - (2 * SkyHour + 2 * Month)

So if the sky hour is 7 at its April then the real time is:
      Time = 41.5 - (14 + 8) = 19.5 = 7.30 pm

Neat!

More detail in "The Natural Navigator" footnotes for the chapter on The Firmament.


11 comments:

O Docker said...

I'm beginning to understand why NASA has such an immense budget.

It must be enormously expensive for them to go up there twice a year and adjust the clock for daylight saving time.

Tillerman said...

Why 41.5? And don't say "Because it gives the right answer." It must be derived from some real world coordinates or something.

theknittingsailor.com said...

I am so excited and confused at the same time.
I may need to go away and lie down while I think about this.

JP said...

O'Docker: LoL!

Tillerman: Oh no! I'm getting homework from my blog! Will have a ponder

Theknittingsailor: even better, go outside this evening and while standing up look up at the night's sky?

Tillerman said...

And could the imaginary clock be oriented a different way so as not give such a weird calculation?

Patrick said...

I would be more excited if the constant in the calculation was 43. Are you sure it's 41.5?

Tillerman said...

It's 43 during Daylight Savings TIme.

JP said...

Obviously it should be 42!

I'm having my own doubts about 41.5 - will post later

Tillerman said...

Yeah if the month is January and the sky hour is 1 o'clock then the formula would suggest that the actual time is 37.5.

JP said...

Mod 24?

my2fish said...

I like Tillerman's #43 better.