Timeanddate.com initially printed this article by Konstantin Bikos and Graham Jones on July 4, 2023. Reprinted right here with permission. Edits by EarthSky.
Final yr, timeanddate.com confirmed an internet meme claiming 99% of the world’s inhabitants will get daylight on the identical time on July 8. The truth is, this occurs on an entire vary of dates … however solely round a particular time of day.
Identical second of daylight for 99% of the world’s inhabitants
It appeared like an implausible declare that circulated the web final yr. And but, our quantity crunchers confirmed it: 99% of the world’s inhabitants actually do obtain a point of daylight at 11:15 UTC on July 8 annually. (That’s should you rely the three% that experiences astronomical twilight, which is hardly discernible from nighttime.)
At that second, most populated areas are on the day aspect of Earth or in one of many twilight zones. The one giant landmasses on the evening aspect are Australia, New Zealand, and elements of Southeast Asia and Antarctica.
July 8 … and different dates
With July 8, 2023, simply across the nook, we determined to develop our focus. We’re additionally answering one or two of the questions which have come our manner since final yr:
- Is July 8 the one date this occurs? If there’s a peak on that date, round 17 days after the June solstice, shouldn’t there be one other one 17 days earlier than the solstice?
- What occurs to the daylight inhabitants numbers if we alter the clock by a couple of minutes?
To reply these questions, we seemed on the variety of folks experiencing day, evening, or twilight at each minute of each day of the yr.
As earlier than, all our calculations are primarily based on timeanddate’s sun data and inhabitants information from the Center for International Earth Science Information Network at Columbia College in New York.
60 situations of worldwide daylight
Because the chart beneath exhibits, July 8 isn’t the one date when daylight reaches all however 1% of individuals on Earth. Removed from it!
The chart beneath exhibits the share of the world’s inhabitants experiencing daytime or twilight at 11 UTC each day of the yr. Notice how the curve approaches the 99% threshold as early as Might, then plateaus for practically all of June, and finally drops again towards the 98% line in mid-July.
In keeping with our numbers, this era begins round Might 18 and ends round July 17. In different phrases, there are about 60 days across the June solstice when, for a couple of minutes each day, 99% of people on Earth get daylight or twilight (rounded to the closest %).
So sure, the declare checks out for each July 8 and June 4 (17 days earlier than the solstice). But in addition for about 58 different days throughout that point of yr.
Each day peak round 11 UTC
You might have observed that we primarily based our chart on the worldwide distribution of daylight each day at 11:00 UTC as a substitute of 11:15 UTC, the time talked about within the unique web meme that we fact-checked final yr.
That’s as a result of our numbers present that, on common, the day by day peak happens nearer to 11:00. On the entire 30 days with the biggest quantity of individuals experiencing daylight, the height second happens between 11:00 and 11:03 UTC. Among the many prime 60 days, it falls a minute or two later in only a handful of circumstances.
The enjoyable truth right here is that July 8 is certainly one of many few dates when the height occurs slightly later: at 11:10 UTC, in response to our calculations. So, though our numbers, on common, favor an earlier time, the creator of the web meme hit the mark exceptionally nicely!
Explaining the wobble
If you happen to take one other peek on the chart above, you’ll discover the road is a bit wobbly. The truth is, that wobbliness factors to one of many causes we discover digging into this information so thrilling!
It exhibits how even the tiny day-to-day adjustments within the distribution of daylight across the solstice can have fairly giant results on the corresponding inhabitants numbers.
A sparsely populated space may be simply contained in the twilight zone on one day and at nighttime on the following; on the opposite aspect of the globe, a significant metropolis might have concurrently joined the twilight zone, inflicting a noticeable bump within the curve.
Asymmetrical rise and fall
On the identical time, the curve isn’t symmetrical in regards to the June solstice or December solstice. Earth’s elliptical orbit is an element right here, inflicting our planet to hurry up and decelerate on its manner across the sun. That is linked to the equation of time, which measures variations within the obvious solar time all year long.
In observe, because of this the sun’s obvious motion throughout the sky barely adjustments velocity, inflicting the second when most individuals get daylight to happen a bit earlier or later from one day to a different.
This causes a slight distortion in our graph, which doesn’t take these variations under consideration, rigidly plotting the daylight inhabitants information at exactly 11 UTC every day.
World’s inhabitants isn’t static
Whereas we’re assured in our calculations and information units, it’s value repeating that figuring out how many individuals expertise day, evening, or twilight at anybody second is a slightly messy enterprise.
For one, the world’s inhabitants isn’t static. It adjustments over time, and in some places, it does so at a special tempo than in others. We primarily based our calculations on the most effective inhabitants information units out there. However they’re from 2020.
What’s extra, the margins are minuscule. Whereas our algorithms did establish a particular prompt when most individuals get a point of daylight – 11:02 UTC on June 23 – the inhabitants numbers for the times on both aspect of this date are only a tiny fraction smaller. We’re speaking just a few tens of hundreds of individuals. Peanuts in comparison with the world’s inhabitants.
Backside line: Reality-checkers at timeanddate.com found it’s technically true that 99% of the world’s inhabitants experiences some daylight at 11:15 UTC on July 8. However there are various different dates the place that is additionally true!
