Astral dark

One of the joys of living outside on the campsite at Walberswick is that you get to see the sky. And you really get to see it, in all its moods and patterns of light.

One thing you notice is how long it takes for the sun to go down on a long summer's evening. And even after it has gone down there is a long procession of an hour or so through all the possible colours until you can actually say it's dark. 

How can you say it is now dark? What test would you use? If I drop an object on the ground , can I see it to pick it up? Can I read the title on the cover of a book? When did night arrive? Is it when you can see the first star? Surely not, because the blue around that is not midnight blue.

So when does it get actually dark? I was surprised to find - but it is always good to learn new things - that there are three defined stages of twilight, depending on how far the Sun has dropped below the horizon (considering it at the end of the day rather than the beginning). These are the three:

Civil Twilight: This is when the Sun is between 6 and 0 degrees below the horizon. Any higher than that and it is sunrise. As you know, in the half hour before the sun comes up, it is pretty much daylight but for the arrival of the big light itself

Nautical Twilight: This is when the Sun is between 6 and 12 degrees below the horizon. It doesn't feel very light, but you can see the horizon and make out many things. 

Astronomical Twilight: This is when the Sun is between 12 and 18 degrees below the horizon. It is nearly full night, but there are still elements of light on the horizon where the sun has set or will eventually rise. It is not quite night, but there are lots of stars in the sky

And finally, when the sun is more than 18 degrees below the horizon, we can call it night or, sometimes, astronomical night, because now the stars can be viewed clearly and fully. In fact, anyone who has stayed up late, or left their tent for a pee at 1 O'clock in the morning knows that is carries on getting darker. Or at least the stars themselves seem brighter, as the background is darker. And the sight of the Milky Way ramping across the sky at such an hour is one to make you catch your breath (and possibly pee on your foot). 

And I for one am dying to get back to Walberswick one moonless clear night to see it all over again.