# sunrise/sunset enroute

Join Date: Aug 2005

Location: fairly close to the colonial capitol

Age: 52

Posts: 1,686

One of my interests PENKO, the sky.

While there are equations you can muscle through on your own, try this Excel spreadsheet http://www.ecy.wa.gov/programs/eap/models/twilight.zip Comes from a Washington state website and is bug-free.

Add 8 minutes for sunset times and subtract 8 for sunrise times at FL350-400.

UTM to Lat/Lon calculators are available, but I just use a simple UTM/Coordinate map.

While there are equations you can muscle through on your own, try this Excel spreadsheet http://www.ecy.wa.gov/programs/eap/models/twilight.zip Comes from a Washington state website and is bug-free.

Add 8 minutes for sunset times and subtract 8 for sunrise times at FL350-400.

UTM to Lat/Lon calculators are available, but I just use a simple UTM/Coordinate map.

Thread Starter

Join Date: Apr 2003

Location: Europe

Posts: 2,991

Thanks for that handy little excel sheet! It beats using awkward tables. But I was actually wondering how to calculate the point at which the sun would rise/set as seen from an aircraft travelling from A to B...

Join Date: Aug 2005

Location: fairly close to the colonial capitol

Age: 52

Posts: 1,686

But I was actually wondering how to calculate the point at which the sun would rise/set as seen from an aircraft travelling from A to B...

You have once again sparked my interest. Will have a look around.

edit: Almost positive dispatch has something that may be useful.

Join Date: Mar 2007

Location: FL410

Posts: 383

I would have thought it would be possible to estimate the time of SR/SS from the Air Almanac.

Its easy to do on a ship to an accuracy of a few seconds from the nautical almanac. Obviously you need your estimated position at Sunset, but then how do you know when Sunset will be? So you need an estimation of when SS will take place. Which on a ship is easy as you can just check when it happened last night.

Obviously you can't really do this on an aircraft because of the speed. For an accurate answer I guess some sort of differentiation would be required. If you can make a reasonably accurate guess of where it will happen, you can work something more accurate out.

Or you could have a look at this:

SunTimes Freeware download and review - geographical time calculator from SnapFiles

Its easy to do on a ship to an accuracy of a few seconds from the nautical almanac. Obviously you need your estimated position at Sunset, but then how do you know when Sunset will be? So you need an estimation of when SS will take place. Which on a ship is easy as you can just check when it happened last night.

Obviously you can't really do this on an aircraft because of the speed. For an accurate answer I guess some sort of differentiation would be required. If you can make a reasonably accurate guess of where it will happen, you can work something more accurate out.

Or you could have a look at this:

SunTimes Freeware download and review - geographical time calculator from SnapFiles

Join Date: Jan 2008

Location: France

Age: 57

Posts: 9

**A simple graph can do this**

You first have to estimate approximately where the sun will rise, this can be done trying a few waypoints along your flightpath.

You then choose one waypoint before the sunrise and one after the sunrise.

You get four times out of that :

- SRA : sunrise at point A

- ETA : estimated time over A

- SRB : surnrise over point B

- ETB : estimated time over B

You can plot this times on a graph, draw the SR line (connect the two dots), draw the ET line.

The lines should intersect, and you can read the time you will see the sun rise.

If you use a chart to do the plotting, the intersection will show the position of the sunrise.

To work properly the points have to be "close", 10° of longitude works well on an Atlancic crossing.

You could also compute the intersection using some simple math, e.g; find the intersection of two lines each defined by two points.

See the picture here : http://tinyurl.com/yfxrf2b

You then choose one waypoint before the sunrise and one after the sunrise.

You get four times out of that :

- SRA : sunrise at point A

- ETA : estimated time over A

- SRB : surnrise over point B

- ETB : estimated time over B

You can plot this times on a graph, draw the SR line (connect the two dots), draw the ET line.

The lines should intersect, and you can read the time you will see the sun rise.

If you use a chart to do the plotting, the intersection will show the position of the sunrise.

To work properly the points have to be "close", 10° of longitude works well on an Atlancic crossing.

You could also compute the intersection using some simple math, e.g; find the intersection of two lines each defined by two points.

See the picture here : http://tinyurl.com/yfxrf2b

*Last edited by pgroell; 30th Mar 2010 at 08:23. Reason: Added link to image*