tag:blogger.com,1999:blog-714718709601620866.post3841328243060960985..comments2024-03-28T04:33:15.006-07:00Comments on David Burch Navigation Blog: Refraction in Celestial Navigation–still an issue, after all these yearsDavid Burchhttp://www.blogger.com/profile/13413234790483329339noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-714718709601620866.post-43449325979367622672022-03-10T23:52:07.752-08:002022-03-10T23:52:07.752-08:00For rise or set predictions the refraction also be...For rise or set predictions the refraction also between the horizon and the eye should be corrected for. Its nominal quantity can be found by comparing the arcminutes of horizon distance and horizon dip. Some sources in the 19th Century estimated it as .16 arcminute multiplied by the square root of the height in feet. So for an observer whose eye is 100 feet higher than sea level the combined refraction would be about 33.8 arcmin + 1.6 arcmin = 35.4 arcminutes. The correction to apparent height would be -35.4 arcminutes.<br /><br />Mark PrangeAnonymoushttps://www.blogger.com/profile/05447542600076145305noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-23556252978592611632020-09-08T11:00:53.921-07:002020-09-08T11:00:53.921-07:00Roughly right. 1' error in sight can be about ...Roughly right. 1' error in sight can be about 1' error in fix, but a fix takes two sights and the way they intersect is not a linear reflection of the sight errors. David Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-76624964600336567782020-09-08T09:26:01.874-07:002020-09-08T09:26:01.874-07:00Thanks, I'll check them out! Perhaps I miss-im...Thanks, I'll check them out! Perhaps I miss-implied what I was asking. If you measure the altitude of star and your altitude is off by 1 deg because you mistook the horizon by that amount (or similarly the local gravity vector)... what would the resulting error in position be (is there a rough estimate, or it totally depends on the situation?)Anonymoushttps://www.blogger.com/profile/13635911618596534324noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-22399694816514932812020-09-08T09:21:54.651-07:002020-09-08T09:21:54.651-07:00Not sure about that effect if notable. You might c...Not sure about that effect if notable. You might check with the folks at the NavList; I think they discuss such things. See http://www.fer3.comDavid Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-52892635575558861222020-09-08T09:17:03.925-07:002020-09-08T09:17:03.925-07:00I'm curious... if there is a good approximatio...I'm curious... if there is a good approximation for the resulting error in position based on error in local gravity vertical (or error in horizon) in the calculations... does it roughly equate to 1 deg equals 60 nm?Anonymoushttps://www.blogger.com/profile/13635911618596534324noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-92139575592896234742019-04-24T06:04:36.145-07:002019-04-24T06:04:36.145-07:00Hohenkerk & Sinclair published their paper in ...Hohenkerk & Sinclair published their paper in 1985, but from the looks of things Garfinkel's model (from 1944) was still used in the Nautical Almanac through 2003. The stars and planets correction tables in the 2003 edition are identical to the <a href="https://catalog.hathitrust.org/Record/006085044" rel="nofollow">1958 edition</a>. And when the standard conditions used for the refraction calculations are listed at the top of page 260, it's not until 2004 that humidity and wavelength are mentioned (which the Garfinkel model didn't take into account).<br /><br />Also, in the 2012 edition of the <i>Explanatory Supplement to the Astronomical Almanac</i> Hohenkerk mentions that the new refraction tables in the <i>Nautical Almanac</i> are now based on a latitude of 45° instead of the 50° implied in Garfinkel's model. <br /><br />So the changes in 2004 seem to be:<br />*model<br />*humidity<br />*temperature lapse rate<br />*latitudeDavid Iwanciohttps://www.blogger.com/profile/13886000007398095423noreply@blogger.com