Many surveyors of my era, when asked what the longest sight line they have ever made, give the wrong answer simply because they don't think of this as a sight line. 

The answer is 430 light years, the object being sighted is Polaris!

Did you know that same sight line  is also the longest made by governmental surveying agencies all over the world?

The USC&GS claims the longest sight they have made between two points on the earth's surface is 193 miles long.

What is the longest surveying sight line you have made on the earth's surface?

David C. Garcelon

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It was a mile (5280 ft) between two section corners in Orlando, FL. Then I made a trip to San Luis Potosi, Mexico where I had an 8500 ft backsight. It was with a Topcon GTS series Instrument with a triple prism.

My longest sight was in the New Orleans, LA area, across the MRGO(Mississippi River Gulf Outlet) and GIWW(Greater Intracostal Waterwal) and the marsh in between the waterways. Total distance was 1.5 miles. I know surveyors up here in Colorado that have taken much farther sites. Don't forget your triple prisms!!!

Just before I was married, so about 1980; using a tellurometer from Flinders Peak in the You Yangs to Black Springs Hill in Mooroolbark, Victoria, Australia. It turned out to be about 84km. Melbourne is about half way between the two points.

My longest foresite was 4.0km in length, in Morocco on a sparse 2D seismic survey. 

Hi David,

I guess mine is like your's ,being Polaris and the Sun (93,000,000 ) miles but lets not forget the people who use the South Pole star Sigma Octantis (Polaris Australis ) ,it is 281 LY from us.The Southern Cross Stars are on many flags with it. I do not really know how far between two points on Earth,since  I have used Radio Tower Lights and offshore Oil Rigs lights both have been very long sightings.  I have used Transits to correct or adjust sighting Transit tables on Fire Towers that you use to locate Fires with by Triangulations from Two or more towers and that was also very long sites.I have also made some very long Distance Shots,but do not know the record for that. I know they can measure to targets placed on the Moon and that is 250,000 +/- miles. But looking at Polaris is still my Favorite sighting.

the longest sight with a single prism I've ever measured was 1.2 km. However you can barely see the prism only the rod is visible due to shimmering.

 

A meagre 15km - but that was for a braced quad in the Grampian Mountains, so no EDM required.

Longest EDM shot probably around a 1.5km to a triple prism. Couldn't see the darned thing, and had to go with the strongest return signal - anything to avoid breaking the ban to enter the golf course! Apparently golf courses aren't keen on by-passes running through them. Who knew?

I've shot lots of points more than a mile away using current technology, but I'm far prouder of the fact that in the 80's, I was accurate to within a foot and a half on shots over 800' using a Wild T-2 and stadia rod.

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