Northern latitudes

Every night we were surprised by how long the twilight lasted.  All the places we stayed had very dark blinds on the windows so you could sleep past 4:00 am when the sun came up.  Scott shared with us that there are actually 3 stages of twilight and dawn:  civil twilight is when the sun is less than 6 degrees below the horizon, nautical twilight is when the sun is between 6 and 16 degrees below the horizon, and astronomical twilight is when the sun is more than 16 degrees below the horizon (the reverse is true for civil dawn, nautical dawn and astronomical dawn).   At 57 degrees North, astronomical twilight is at 1:00 am, meaning until then the skies are too bright for astronomers to make observations of the deep sky.  These are called "grey nights".  Above 60 degrees astronomical twilights doesn't occur at all in the summer (the sun never gets below 16 degrees of the horizon).  In these regions it is called "white nights".  Above 66 degrees North, the sun never actually sets and this is called the Midnight Sun.

Edinburgh is at 55 degrees north, and Dunvegan and Granton on Spey are at 57 degrees North - experiencing grey nights.