# How far can I see?

Yes, I know the answer is an awful long way (i.e. to some quite distant galaxies), but I specifically mean in the context of how far can I see as I go up in altitude? From my third-floor office window in Hamilton I can easily see the 50 km to the top of Te Aroha (the mountain, not the town) on a clear day, but from 37000 feet altitude on a plane, just how far can I potentially see?

The relationship between the distance to the horizon and your altitude is quite a simple one. At an altitude of just 5 metres, the horizon is 8 km away, though you’ll need somewhere very flat without any trees to experience this.  Then, as you quadruple your altitude, the distance to the horizon doubles. Thus, at a height of 20 metres, you will see 16 km (assuming a nice clear atmosphere). At a height of 80 metres (four times 20), you will see 32 km. At 950 metres (Mt Te Aroha), the horizon is about 110 km away (which is why I can see the summit from my office window), although you’d probably struggle to see that far on all but the most extremely clear of days. (When I was up there I was struggling to see 110 metres).

And finally, in a window seat on an Airbus A320 at 37000 feet over the Australian outback, the horizon sits an impressive 350 km away.  That’s a lot of empty land to look at. Though note that the plane could cover that distance in about 20 minutes.

As I said, over the holiday season blogging is likely to be a little slow, but we’ll see what I can find for you. Have a Happy Christmas and great New Year