If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
official sunset/sunrise
On Apr 19, 9:05*pm, brian whatcott wrote:
Darryl Ramm wrote: * /snip/ You can see how this could vary when the horizon is the Rockies, versus five miles West where it might be 5000 ft lower... Brian W Stop tying to make this hard, there is one proper definition to worry about for gliding in the USA. That is the table generated by the US Naval Observatory. The FARs *define sunset times as published in the Air Alamanac which is produced by the US Naval Observatory, but for practical purposes the official data is the USNO tables /snip/ Darryl I have no problem with competitive sporting endeavors adopting a uniform definition of anything they choose to. * * But supposing that the Official Definition of Sunset from the USNO and the ACTUAL sunset time, as described by the USNO, always coincide for a particular place and time would be an over simplification. At times, a LETHAL over-simplification. Take this NTSB accident investigation from April 15th, 2002 for example. http://www.ntsb.gov/recs/letters/2002/A02_08.pdf Here an aircraft landing in the Rockies failed to note an intervening summit. It was subject to a LOCAL sunset that was 25 minutes earlier than the official sunset time as pointed out by the USNO in a footnote, mentioned in this report. Brian W Again the OP was a question about official sunset times. The official definition of Sunset by the USNO is what they use to generate the table. There is no conflict between USNO definition and their own tables, do you really think there would be? This is not an arbitrary SSA sporting definition, the SSA is ensuring glider badge and record flights comply with the strict sunset flight requirements described in the FARs (unless you can show you are legal to fly to civil twilight). USNO Definition: "Sunrise and sunset. For computational purposes, sunrise or sunset is defined to occur when the geometric zenith distance of center of the Sun is 90.8333 degrees. That is, the center of the Sun is geometrically 50 arcminutes below a horizontal plane. For an observer at sea level with a level, unobstructed horizon, under average atmospheric conditions, the upper limb of the Sun will then appear to be tangent to the horizon. The 50-arcminute geometric depression of the Sun's center used for the computations is obtained by adding the average apparent radius of the Sun (16 arcminutes) to the [So presumably by incorporation via the Air Almanac reference, this is pretty much the technical description of Sunset referred to in the FARs] I hope pilots get this is a numerical model, they should especially when presented with a relatively crude table. They need to take into effect local conditions that affect safety, whether it be terrain, weather etc. that can all affect local light. But again that was not the question being asked, which was about official sunset times. Darryl |
#12
|
|||
|
|||
official sunset/sunrise
Stephen! wrote:
brian whatcott wrote in news:6 : I have run into a definition of sunset that used to go like this: "The time at which the trajectory of the Solar center is six degrees below the local horizon." You can see how this could vary when the horizon is the Rockies, versus five miles West where it might be 5000 ft lower... Using that logic one could say that sunset occurs at 1500 when you are on the west side of a deep north/south canyon... After all, you can't see the sun anymore when it goes behind the mountain. It must be sunset, no? The horizon is the horizon, regardless of the local topography. Not only could I say that actual sunset might be premature into a high Rockies field, but more importantly, an accident investigation board could say that, with backing from a USNO spokesman for that particular accident site in the Rockies. But as someone has pointed out, an official FAR night definition which is good for most times and most places is a different proposition than the odd exceptional cases which contribute at times to getting pilots killed. Brian W p.s. that old definition I (mis)quoted was apparently intended as a definition for NIGHT rather than sunset, apparently. |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Sunrise | Patrick R7 | Aviation Photos | 2 | October 19th 08 11:10 AM |
Col. Robert Bowman, PhD, U.S. Air Force (ret) - Director of Advanced Space Programs Development under Presidents Ford and Carter. "A lot of these pieces of information, taken together, prove that the official story, the official conspiracy theor | Custard Cream | Naval Aviation | 10 | July 14th 07 06:51 PM |
Sunrise, Sunset -- the real data, for anywhere in the world | [email protected] | Piloting | 8 | June 30th 07 02:59 AM |
Jet Sailplane at Sunset | Bob C | Soaring | 0 | June 27th 07 07:16 AM |
Japan Airlines_Early Bird Sunrise | Ducky | Aviation Photos | 0 | February 8th 07 07:31 AM |