As far as I have been able to gather, the longest I can find that stays on the island of Ireland is that Caherconree near Camp, Kerry should be visible from Croaghaun, Achill at 199.6km.
Other interesting long sightlines are:
- Galtymore to Croagh Patrick for 183.9km
- Galtymore to Slieve Anierin NE of Drumshambo, Co. Cavan for 192.5km
- Brandon to Slievemore on Achill for 197.8km
To get longer sightlines than 200km one would have to look over to the UK.[LIST][*]Errigal can see 202.9km to Ben More on the Isle of Mull.[*]Lugnaquilla can see 206.9km to a hill between Llyn Brianne and Claerwen Reservoir in central Wales. [*]But, the current max distance I could find was from Slieve Donard to a secondary 759m peak of Penygader, SW of Llyn Cau and not far from the Mach Loop, for a distance of 212.5km
I've been using the panorama generator at udeuschle.de for this exercise, as it gives a handy max-distance-viewable. Though I know the results may vary depending on refraction, it's been fairly accurate from what I've seen so far.
Personally, I've seen Nephin from the top of Keeper Hill for a distance of 158.3km on a lovely transparent day a few years ago (and got a crappy pic of it too).
Does anyone know of longer or better sightlines on or from Ireland?