So that gives us 93% of the world’s population with enough light to walk around without running into things. So let’s count half of those people in Nautical Twilight - in other words, about 3% of the world’s population - as having enough light to get around. Now it gets tricky.Įarly on in Nautical Twilight there’s enough light to get around, but later in Nautical Twilight, it’s pretty dark. Another 6% of the world’s population, at 8:15 pm Sydney time, July 8 were in Nautical Twilight. That adds up to 90% of the world’s population. So let’s put it all together forJuly 8 at 8:15 pm Sydney time.įirst, 83% of the world’s population could see the Sun – depending on the local horizon and the local cloud cover.Īnother 7% were in Civil Twilight, where they could walk around perfectly easily with no problems. But astronomers are more picky, and there’s still too much light to see the stars really well. For you and me and the sailors, this is effectively night-time. Astronomical twilight runs from when the centre of the Sun shift from 12° to 18° below the horizon. The third type of twilight is called Astronomical Twilight. But in Nautical Twilight there are enough stars to begin navigating again. Sailors can navigate in the daytime because there’s the Sun, but they can’t navigate in Civil Twilight because there’s no Sun, and not enough stars. ![]() ![]() The second type of twilight is Nautical Twilight - which runs from when the centre of the Sun drops from 6° below the horizon, to 12°. In Civil Twilight you can just begin to see the brightest planets (such as Venus) begin to appear. In Civil Twilight, there’s enough light to see what you’re doing, but street lights and car headlights begin to switch on. The three versions of twilight are Civil Twilight, Nautical Twilight, and Astronomical Twilight.Ĭivil Twilight begins when the last of the sun vanishes below the horizon, and continues until the centre of the Sun is 6° below the horizon.īy the way, 6° is roughly 12 times the diameter of the moon or the Sun, which are each about half a degree in diameter. Now the next thing to consider is that there are not just one, but three official, and quite different, versions of twilight - that fuzzy boundary between the Sun being above the horizon, and full darkness where the stars are completely visible. But if you give just a few more weeks for the Sun to move further South, there’ll be more light for an extra 10 million people in those islands. On the actual solstice of 21st or22nd June, they are partly in the dark. Well, near the equator, Indonesia and the Philippines are very highly populated. And going a bit further to the right, you’ll see that both Australia and New Zealand are well and truly in the darkness of night.īut we get more people in day time a few weeks after the June solstice – how come? Now if you go to a readily available time and date website, andcheck out the little map that shows you where sunlight is falling on the planet at 8:15 pm Sydney time a few weeks later (than the summer solstice)on July 8, you’ll see on the left-hand side of the map that the shadow of nightfall just misses both North and South America – with a fuzzy boundary (that’s twilight).Īnd on the right-hand-side of the map, again you’ll see that the shadow of nightfall misses the mainland of Asia as well as Japan and Taiwan. So the Northern Hemisphere gets much more light than the Southern Hemisphere. So at the June solstice - which happens every year around the 21st or the 22nd of the month- the North Pole is in continuous 24-hour sunlight, while the South Pole is shrouded in perpetual darkness. The second thing is that the Earth doesn’t spin around a vertical axis, but is actually tilted from the vertical by about 23.5°. Now the first trick here is to realise that about 90% of all humans live in the northern hemisphere. So how can anyone expect me to believe that on July 8, in the year 2022, at 8:15 pm Sydney time, “99.164% of the world’s population is between dawn and dusk”.īut, it turns out that this quote is not that wild. In your mind, you’re probably seeing half the globe lit by sunlight, and the other half in shadow – or night time. Now imagine the Sun is shining its light onto the Earth. Most us accept that the Earth is a globe, that orbits the Sun over a period of a year.
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