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Re: Precomputation- was Sun lines was Moonrise video
From: Gary LaPook
Date: 2013 May 5, 01:37 -0700
From: Gary LaPook
Date: 2013 May 5, 01:37 -0700
| The other way to adjust the Hc derived at a specially chosen AP to compute the Hc at the destination (or at any DR position) is to apply the”delta T” and the “delta L” corrections using the method laid out in H.O 214. Unfortunately the tables for doing this are not included in H.O. 249 or in H.O. 229. The “delta T” correction adjusts the Hc to the longitude of the DR (destination position) and this is a simple straight line interpolation between successive value of LHA. Looking at H.O 249 for LHA 272 and 273 we see the the tabulated Hc goes from 2̊ 14' to 3̊ 09', a change of 55' minutes of altitude for a change in longitude (LHA) of one degree, 60 minutes. The difference in longitude between the assumed longitude, 177̊ 02.5' and the longitude of Howland, 176̊ 38' is 24.5'.so we just multiply this “delta T” by the number of minutes of the difference of the longitudes, 55 x 24.5 (we can use the multiplication table in H.O. 249 for the standard “delta d” correction). Since it is obvious that Howland is closer to the sun than the chosen AP then the altitude measured at Howland must be larger than that derived at the AP and this factor is a plus 22.5'. We also make the adjustment for the difference in latitude between the DR latitude and the latitude of the AP. The latitude of the AP is 1̊ North and of Howland, 0̊ 48' North so the difference in latitude is 12'. Looking at the “delta L “ table we see that the correction is 4.7' and we can determine the sign by comparing the altitudes for two succeeding latitudes. The latitude of Howland is 12' south of the AP so the sign of this adjustment is minus. Combining this -4.7' with the “delta t” correction of + 22.5' gives us the total adjustment that must be applied of +17.8', the equivalent of the + 18' we found graphically. See: http://us.mc1810.mail.yahoo.com/mc/s howMessage?fid=Sent&filterBy=&.rand=2054209808&midIndex=10&mid=2_0_0_2_3370675_AN7HimIAAGSbUYR7bApJQ0eeRw8&fromId=&m=2_0_0_2_3374262_AN%2FHimIAAYXCUYU4MgfE8UJi4qI%2C2_0_0_2_3373494_ANzHimIAAIbsUYUzWgc0%2BRmVJlM%2C2_0_0_2_3372649_AN7HimIAALegUYTTSwrQJgyHgQE%2C2_0_0_2_3372017_AN%2FHimIAAUUqUYSG%2FwfgLX8tkrc%2C2_0_0_2_3371496_ANvHimIAACyLUYR%2ByAl7g00SGQ0%2C2_0_0_2_3370675_AN7HimIAAGSbUYR7bApJQ0eeRw8%2C2_0_0_2_3369822_AN3HimIAALM8UYRrsQWE3yXa%2FFA%2C2_0_0_2_3368979_AN%2FHimIAASkJUYRl4AvR5jHIJaM%2C2_0_0_2_3368540_ANzHimIAAGbRUYQ4vQZmiDJi6nA%2C2_0_0_2_3367688_ANrHimIAAKMQUYNxQQBD0SZnT88%2C2_0_0_2_3366860_AN7HimIAAQHhUYNopQmbbxEiWjo%2C&sort=date&order=down&startMid=0&hash=8ca7420f88593a666c730171b2323e87&.jsrand=1270322&acrumb=e0%2FraMWZT1w&enc=auto&cmd=msg.scan&pid=2&tnef=&fn=Delta+latitude+correction+tables.pdf http://www.fer3.com/arc/img/105707.ho214-delta%20lat.pdf gl --- On Sat, 5/4/13, Gary LaPook <garylapook@pacbell.net> wrote:
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