3 weeks 9 hours
A Gold Star or a Big Red Cross
Submitted by Leslie Peart on Sun, 04/12/2009 - 19:00
I had really been looking forward to Easter Sunday on this wide expanse of Pacific. I had often heard about holidays on The JR and this was my opportunity for first-hand experience.
The barbeque was planned and the fire and safety drill was postponed to Monday so as not to interfere, but something about yesterday's wind made me worry.
Maybe I could get up for sunrise? That's something I've never been able to manage for Easter and maybe I could salvage something of the holiday just in case the barbeque was cancelled. So I emailed Captain Alex about sunrise and the forcast. I found his answers very interesting and I hope that you will too. Grab your dictionaries!
Leslie...during my after dinner sugar low
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
From Captain Alex regarding Easter Sunrise:
On Easter Sunday the sun's declination will be 8 deg 51 mins North and the latitude of The JR is at 8 deg 00 min North. Whatever your longitude is on Easter Sunday, the sun will rise at 05h 52m 48s local mean time or LMT. However, nobody keeps LMT unless, by fluke, your exact longitude is a multiple of 15 (15 degrees of longitude equals one hour). Therefore we have to correct the LMT of our position to the GMT-9 zone time that the ship is keeping. Longitude of the ship is 131 deg 58.5 mins West which is equal to GMT- 8 h 47 m 54 secs, which is 12 m 06 secs earlier than GMT -9. Therefore the sun will rise in our position at 05h 40m 54s.
Now in order to check this answer with your chronometer you will need to know the definition of sunrise. Mostly due to refraction you will actually see the sun before sunrise. The official sunrise is when the lower limb of the heavenly body is observed to be 1/2 a diameter above the horizon. At this point you will be able to click your stop watch and award a gold star or a great big red cross.
Also at this time if a bearing is obtained from the gyro or indeed magnetic compass you will be able to assess the error of the compass.
ie Sin Amplitude = sin Declination Secant latitude
= Sin 8 deg 51 min Sec 8 deg 00 min
= 0.15385 x 1.00983
Amplitude = 9 deg..... (since we are talking about sunrise the answer is applied to the East and since declination is North it is applied to the North.)
Therefore the true amplitude of the sun at sunrise on Easter Sunday is predicted to be E 9 deg N or converted to a bearing = 081 degrees true.
All that said, you could simply check the GPS.
Now, about the forecast, the science of weather prediction is less accurate than astronomy or navigation so I'll just keep my fingers crossed like the rest of the crew.
Photos: Top: At least the cake was delicious, as was the rest of the meal, even when served indoors because of....rain. Middle: The sky at 05h 40m 54s (or there abouts) looking toward 081 degrees true. Sunrise? You be the judge. Credit: Leslie Peart, Deep Earth Academy and IODP Education Director.