Christmas Countdown, Sunday #4

Christmas Countdown Sunday’s theme is Other Holidays. Today, we present a Pagan Celebration of the Winter Solstice at Stonehenge in the UK.

Sunday’s theme is “It’s not just Christmas,” and it’s appropriate to have this one the day after tomorrow is the winter solstice. In pagan cultures, this is called Yule, hence all those yuletide log things in your Christmas carols.

The idea of celebrations occurring around the solstices and equinoxes is something that has been baked into humanity since the beginning, especially after we went from being nomadic hunters to settlers with agriculture.

It became very important to predict when to plant, when to harvest, when to expect what kind of weather, and the only clocks we had were in the sky — the Sun and the Moon. That’s why we measure days by the Sun and months by the Moon — indeed, in many languages the words for “month” and “Moon” share the same root.

The two most important of the four equinox/solstice times are the one that comes tomorrow, the winter solstice, and the one that comes three months later, the vernal equinox, “vernal” meaning the same thing as spring.

The reason they became so significant is that the Winter solstice is right at the time when the period of daylight in the northern hemisphere is the shortest and the world is dominated by the night. Solstice refers to the idea of a standing or stopping and, indeed, if you look at the analemma of the Sun, you’ll see that the images clump together at the bottom (start of local winter) and the top (start of local summer.)

As for the vernal equinox, this is the day when sunlight and darkness are equal and periods of daylight start to get longer until they hit their maximum on the summer solstice in June.

I think you can see why agricultural societies would find these dates so important. By the start of winter, all of the crops should be in and everything should be stored up to survive the long, cold winter until planting could begin once the ground began to thaw in the spring.

So… they kept an eye out for the day with the least sunlight, then counted thirteen phases of the Moon. This is why so many cultures in the northern hemisphere have big and important holidays, both religious and secular, in late December and late March, and more minor celebrations in late June and late September.

And, to further subdivide it, there are important events in early February (Candlemas or Groundhog Day, anyone?), early May (Beltane/May Day) early August (Lamas Day), and early November (Halloween/All Saints Day).

That was the long way around of saying that it’s totally appropriate for this group of Pagans to be celebrating the solstice at Stonehenge, because the entire structure seems to have been one huge calendar and observatory, lined up so that the way the Sun hit different stones inside let the people know exactly what day it was.

And, ignoring the differences in liturgy and beliefs, isn’t this observation pretty similar to any other religious celebration? People gathered together in a sacred place to sing, connect with each other, and celebrate something beyond to unite them and bring hope.

In this case, these people are actually celebrating the Sun, the Moon, and Mother Earth, and those three things could not be more important to the continued existence of our species and, indeed, every living thing on this planet.

Wednesday Wonders: Equinox

Welcome to September 22, the date in 2021 when the Earth stands up straight and faces the Sun head on. Well, side on. The point is that on this date the Earth’s poles point at exact right angles to the Earth’s orbit around the Sun, so it marks a change of season. If you’re in the northern hemisphere, this is the first day of fall, and days will begin to grow shorter as the north pole starts to tilt away from the Sun. Meanwhile, if you’re in the southern hemisphere, today is the first day of spring, as the south pole starts to tilt toward the Sun. Oh, don’t worry, though. It’s not like the Earth is literally rolling over. The actual angle of its axis is always the same — it’s just its position relative to the Sun that changes, depending upon which quarter of its orbit it’s in. Today, though, magic happens, as the length of day and night everywhere on the planet is the same — but it’s not 12 hours, because a day is not quite 12 hours. Rather, one day is 23 hours and 56 minutes, so on this day each side of the globe receives 11 hours and 58 minutes of daylight. Close to 24, but no cigar. Each day is missing four minutes, and yes, over the year, the time on your clock technically gains because of this, but that is part of why we have leap years and all that shit in the first place. And the fact that the Earth’s axis is tilted and the apparent height of the Sun in the sky plus the length of day changing regularly is probably what led to human civilization in the first place. As soon as people noticed that the spots on the horizon where the Sun rose and set day-to-day changed, and then started to notice how high it did or did not make it into the sky by noon got folk to taking notes. Next up would have been timing the periods between its rise and set over the course of… well, it’s not defined yet. Figuring out the timing might have been tricky when there was no way to actually tell time, so maybe those first experiments just meant tracking the length of an object’s shadow right as the Sun rose and when it set, them recording the length of each one and comparing it to each subsequent day. This wouldn’t give you a length in terms of hours per se, but it could tell you, for example, how long the shadow on a particular day was. Since the Sun doesn’t cast shadows at night, this gives you length of daylight, and you can then compare that length to the length on other days. This will tell you the rate of change per day, as well as give you the relative lengths of longest and shortest days. Repeat the experiment until the pattern starts to repeat — i.e., you hit the same shadow length you started with and see the same lengths appear over the next, say, dozen measurements, and now you suddenly know how many day/night periods there are before the Sun returns to where it started. People may not have understood the concept of orbits yet and probably thought the Earth was at the center of everything, but only because that’s exactly what it does look like from down here, but it did give them a starting point from which to be able to predict the regular course of the Sun. Finally, key these measurements into the seasons, as in when is it cold, when is it time to plant, when does it flood, and when can we harvest? Eventually, over time, ta-da: You’ve created the calendar, and the basic parameters of Earth-Sun dynamics, plus axial tilt dictate the creation of four annual divisions; call them seasons. Of course, some cultures, who tended to not be agricultural, watched the Moon instead, and also divided the year into months (literally named for moons in many different languages) although not seasons. However, since the lunar month wound up much shorter than the solar month after one Earth orbit was divided appropriately, lunar calendars would always lag behind. This is why, for example, the Hebrew calendar has to add in an entire month every so often instead of just a day, and why Jewish and Islamic holidays seem to slip around the Gregorian calendar. Here’s a nice irony, though. The ultimate holiday for once-a-year Catholics, Easter, is itself set based upon a lunar calendar. The date of Easter is set as the first Sunday after the full Moon that occurs on or after the spring equinox. If that equinox is on a Sunday itself, then Easter is the next Sunday. Why this is the case, I have no idea — but events in the Islamic Calendar, as well as things like the Chinese New Year, are also set based on a particular New Moon, although they are all at different times of the year. If you’re part of the early agricultural movement, though — which led to permanent settlements and cities and irrigation, and all kinds of fancy shiz — then your city is probably going to have a nice observatory, but it wouldn’t be bristling with telescopes, which would not be invented for thousands of years. Rather, it would be a prominent building or even a temple-like structure — think Stonehenge — with very specific architectural features designed to align with the movement of the Sun, Moon, and possibly certain stars to become one giant indicator of when those significant dates passed. For example, a slit in one wall might direct sunrise light on the first day of summer onto a specific plinth or marker, or maybe even a mural or statue depicting the god or goddess of the season. Likewise, the same slit would hit a different marker for the first day of winter. Those two are easy because the sun will be at its northernmost point when summer starts and its southernmost when winter starts, which is why you can use the same slit. Spring and fall, being equinoxes, both come in at the same angle, so the light would hit the same place. However, the good news is that if you know which one was the last season, then you know what’s coming, so spring always follows winter and fall comes after summer. Somewhere around these times, these early astronomers may have even figured out the concept of the analemma and begun tracking it. This is the huge figure-8 pattern that the Sun, when recorded at the same time each day (usually noon) makes over the course of a year. Tracking the Moon would probably allow for the ability to predict solar and lunar eclipses — at the time, probably more useful as a political/religious function over anything else. “The Moon is going to die on Tuesday, and it will be your fault unless you pay us tribute and fealty, peons!” Ewww. Out front would be a huge sundial to impress and mystify the populace who, of course, would never be allowed inside such a sacred space. Same as it ever was. Except… We do have access to this knowledge now, and the short version of it is this. The Sun is the center of our Solar System, mostly by virtue of having 99% of its mass, and holding everything else in its thrall via gravity because of that. There are two planets closer to the Sun than Earth — Mercury and Venus — and both of those are barely titled. Mercury is off-axis by barely 3 hundredths of a degree, while Venus is inclined at 2.6 degrees. However, since Mercury is tidally locked with one side boiling and the other frozen, it’s not likely to benefit at all if it suddenly tilted. As for Venus — this is our solar system’s true shit-hole planet, with the hottest temperature and thickest atmosphere, a hellscape where it rains sulfuric acid constantly. If we look at the rest of the solar system, the only planets that come close to having the same axial tilt are Mars (25.19º), Saturn (26.73º) and Neptune (28.32º). Meanwhile, the planet Uranus has the most extreme tilt in the solar system, with its axle rolled over a full 97.77 º, which indicates that, at some point in the past, Uranus must have gotten rammed pretty hard by some asteroid or even a small planet. The end result is that Uranus always keeps its pole pointed at the Sun, alternating between north and south so that its seasons basically travel sideways — although those seasons aren’t much to speak of there, because the surface is pretty much a nearly featureless ball of methane with some lighter clouds in high latitudes (or is that high longitudes?) and, as recent studies have determined, there is also a big, dark spot on Uranus. Of course, we wouldn’t even know about the other planets and stars and so in if we hadn’t started looking up to figure out what was going on with our own Sun and Moon in the first place, and Uranus, Neptune, and Pluto (not a planet) were not even discovered until modern times. Uranus wasn’t even named until the late 18th Century, but the convention of naming planets over Roman gods carried on, and the place got its name at the suggestion of German astronomer Johann Elert Bode. Whether or not he knew about the comedy potential in English of that name choice is anyone’s guess, but officials agreed. And although it’s properly pronounced “OO-ra-noos,” almost no one says it that way, and so stories about the sixth planet are always unintentionally hilarious. And it all started in ancient days, when the first farmers started to pay attention to the change of seasons and tried to learn whether the gods had left them in clues in the heavens above, eventually leading to an understanding of the cosmos that required no gods at all but adhered to its own inexorable set of laws that were an intrinsic property of reality itself. Thanks, farmers! Images: (CC BY-SA 2.0)

Sunday Nibble #66: Putting the Sun on pause

Happy summer solstice! This is the day of the year in the Northern Hemisphere with the longest period of continuous sunlight, which increases with latitude.

On the equator, at 0 degrees latitude, day time and nighttime are pretty much equal all year long. The farther north you go, the longer the period of sunlight. At my latitude, which is about 34 degrees north, we’ll get 14 hours and 26 minutes of sunlight on that day.

When you get to Reykjavik, Iceland, you’ll experience 21 hours and 8 minutes of sunlight plus 2 hours and 52 minutes of twilight, which adds up to 24 hours during which the sun never really sets, and if you make it to the North Pole, you’ll experience a full 24 hours of sunlight.

It’s exactly the opposite in the Southern Hemisphere, where this is the winter solstice for them, and the period of the longest nighttime, which works in a similar fashion to the north but in the opposite direction, with the night getting longer the farther south you go.

Don’t worry, though. In December, the tables are turned, and then it’s the summer solstice in the south and the winter solstice in the north.

The word “solstice” is derived from the Latin word for stopped or stationary, and this comes from what the Sun apparently does. From the time of the winter solstice, the Sun appears to climb higher and higher into the sky and it continues to do so for six months.

Then, on the summer solstice, it reaches its highest point and then appears to pause for about three days before turning around and heading back down toward the equator.

The mid points are the equinoxes, which is when the Sun’s apparent position is crossing the equator, and this is when all points on the planet have day and night time of equal length regardless of hemisphere.

We have two equinoxes, vernal and autumnal, more commonly known as the spring and fall equinox, which mark the beginning of these seasons.

Put all four together in order, and there you have humankind’s original and most basic calendar. Once the pattern had been recorded and recognized, annual events became much more predictable — the change of seasons, the likelihood of seasonal flooding, and so on.

The Moon became a secondary counter and, in fact, we landed on the idea of a lunar calendar long before the solar one. The word “month” is derived from “moon,” and one month is approximately the length of one complete cycle of the Moon’s phases, from one full Moon to another — or one new Moon to another, depending on your culture’s preference.

So why do equinoxes and solstices and seasons happen in the first place? By the very fortunate circumstance that the Earth’s axis is tilted at about 23 degrees relative to the Sun when it’s at either solstice, and the tilt remains constant relative to the Earth.

It’s probably best demonstrated with an animation to make the concept clear, so here you go, courtesy of YouTuber Brad Freese:

From the Sun’s point of view, the Earth keeps tilting back and forth as it goes around. Meanwhile, to the Earth, it looks like the Sun is bobbing up and down. The end result is the same either way: changing period of daylight that are more extreme the closer you get to the poles, seasons, and the origin of the first human calendar.

Now, a year generally has 12 full moons in it but the number of days in a lunar year, 354, is a bit short of the solar year of 365.25 days, so about every two and a half years, we get that elusive (or not so much) Blue Moon, which is just the 13th full moon of a calendar year.

But when you take 12 and divide it by 4 — the number of solstices and equinoxes — you get a nice even number, 3. So divide each solstice or equinox into three “moons,” or months, and all you have to do then is watch the phases of the Moon to know when the seasons will change.

You might have noticed that neither the lunar days nor the solar days quite add up to the number of degrees in a circle, which is 360. But add them together, rounded — 354 + 365 — and you get 719. Divide that by 2 and round it again, and you get 360.

This is actually a really interesting number, because it has so many factors, which are numbers it can be evenly divided by. If we include 1 and 360, there are 24 of them (24 being a factor of 360), and in fact every single digit number except 7 is a factor, which is very useful.

Beyond that, a lot of the numbers relate to units of time we still use now, particularly 12, 15, 24 and 60, and it’s divisible by 10, which makes it very compatible with our common base 10 system.

By the way, the Babylonians, who were big astronomers themselves, used a Base 60 system, in which the number 360 would have been expressed as their equivalent of 60.

It’s interesting to think that the larger parts of our timekeeping system are not as arbitrary as they might seem and have a strong basis in reality. As for how we chose to count weeks and the hours in a day, that’s part is totally arbitrary.

We could have just as easily divided each day into 36 hours of 40 minutes each or 18 hours of 80 minutes each, but we didn’t. Why? Who knows, but the most likely explanation is that 12 hours of “day” and 12 hours of “night” just echoed the annual pattern nicely.

Hours, by the way, were the very last thing to be measured and determined, since if you just divided amount of daylight by 12, the length of the hour itself would change throughout the year The more important markers were sunrise and sunset.

By the way, a word about the image up top. This image is what’s called an “analemma,” and it represents the position of the Sun in the sky over the course of the year, in this case, in the Northern Hemisphere. The points where they cross represent the equinoxes.

Also note that the top half forms a smaller loop than the bottom half. That’s because of a nice quirk of orbital mechanics. The Earth is at its farthest point from the Sun around the beginning of July, right after the northern summer solstice, and at its closest around the beginning of January, right after the northern winter solstice.

So… in July, the planet is actually moving at its slowest because it basically reaching the “top” of the orbit. That is, the Sun’s gravity has flung it as far away as it’s going to get, so it’s now going to slow down and come plunging back. Think of it like throwing a baseball in the air.

Once the Earth has passed through the equinox again, it’s now being pulled in by the Sun, so moves a lot faster in the same period of time.

But what I really wanted to point out was this. Although astronomers insist that “Uranus” is actually pronounced “oo-ra-NOOS” in order to avoid immature jokes, what did they name this image?

Analemma.

Anal Emma. Yeah, those mofos knew exactly what they were doing.

Image source: Giuseppe Donatiello, (CC0), via Wikimedia Commons

Wednesday Wonders: A busy day in space

Happy New Year! And happy first day of spring!

Wait, what… you say those things aren’t today, March 25th? That the latter was six days ago and the former was almost four months ago?

Well… you’d be right in 2020, but jump back in history to when the Julian calendar was still around, and things were dated differently. This led to the adoption of the new Gregorian calendar, but since it was sponsored by the Pope, not everyone switched over right away. Long story short, Catholic countries like Spain, Portugal, and Italy adopted it immediately in 1582. Protestant countries held out, so that places like England (and the colonies) didn’t switch until 1752.

That was also when England moved New Year’s day back to January 1, which is itself ironic, since it was the Catholic Church that moved the day from then to March 25 at the Council of Tours in 567, considering the prior date pagan, which was probably accurate, since the Romans had moved New Year’s from March to January 1st when they deified Julius Caesar after his assassination.

The practical reason for switching calendars was that the Julian calendar lost 11 hours a year, which added up fast, meaning that entire extra months had to be added between years to set things right again. The Gregorian calendar is much more accurate, although about 2,800 years from now it will have lost a day.

By the way, the religious reasoning for picking March 25th is that it was the Feast of the Annunciation, meaning the day that the Archangel Gabriel appeared to Mary to let her know that she was going to get knocked up by god — although it doesn’t get mentioned canonically until a century after the ol’ calendar switch-a-roo.

Anyway, the math isn’t hard to do. March 25th is exactly nine months before Christmas. And in strictly astronomical terms, the former is the first day of spring and the latter is the first day of winter. Just psychologically, the Vernal Equinox, which is now closer to the 19th or 20th, is the better New Year’s Day option because it’s when days start to get longer than nights, vegetation starts to grow anew, and nature awakes from its slumber.

Note: Your mileage in 2020 may vary.

It’s kind of ironic, then, that today marks the birth of a German astronomer and mathematician, Christopher Clavius, who was instrumental in doing the calculations necessary to figure out how much in error the Julian calendar had become, and then to come up with a calendar to fix it and a method to transition.

This is where the Catholic Church came into it, because Easter, being a moveable feast based on the Julian lunar calendar, had been slipping later and later into the year, threatening to move from the spring to summer. Clavius’s job was to bring it back toward the vernal equinox.

He succeeded to the degree of accuracy noted above — only a day off in 3,236 years. Not bad. This was also when New Year’s Day went back to January 1st, per the old Roman style, and while this is attributed to Pope Gregory XIII, I can’t help but think that Clavius had a hand in implementing the change.

I mean, come on. You’re handed a chance by the most powerful person in the western world at the time to move a major holiday off of your birthday so that your day is finally special on its own? Who wouldn’t do that given the power?

Good ol’ Chris did make other discoveries and get some nice presents, like a crater on the moon named after him, as well as the moon base in the movie 2001.

Still, even if the equinox did move away from March 25, the date still keeps bringing special things for astronomers. It was on this day in 1655 that the Dutch physicist and astronomer Christiaan Huygens discovered Saturn’s largest moon, Titan,

Huygens also has another time connection, though. Where Clavius gave us a calendar accurate to over 3,000 years, Huygens gave us a clock that was the most accurate for the next 300 years. His innovation? Put a pendulum on that thing and let it swing. He literally put the “tick tock” in clock.

Why was this possible? Because the swing of a pendulum followed the rules of physics and was absolutely periodic. Even as friction and drag slowed it down, it would cover a shorter distance but at a slower pace, so that the time between tick and tock would remain the same.

The pendulum itself would advance a gear via a ratchet that would turn the hands of the clock, and adding kinetic energy back into that pendulum was achieved through a spring, which is where that whole “winding the clock” thing came in. Tighten the spring and, as it unwinds, it drives that gear every time the pendulum briefly releases it, but thanks to physics, that pendulum will always take the exact same time to swing from A to B, whether it’s going really fast or really slow.

Back to Huygens’s discovery, though… Titan is quite a marvel itself. It is the second largest natural satellite in our solar system, taking a back seat (ironic if you know your mythology) only to Jupiter’s Ganymede. It is half again as big as our own Moon and 80% more massive. It’s even bigger than the planet Mercury, but only 40% as massive, mainly because Mercury is made of rock while Titan may have a rocky core but is mostly composed of layers of different forms of water-ice combined with ammonia, and a possible sub-surface ocean,

Titan also has a thick, nitrogen-rich atmosphere, the only other atmosphere in the solar system besides Earth’s to have so much nitrogen in it. In case you’re wondering, Earth’s atmosphere is almost 80% nitrogen — OMG, you’re breathing it right now! But this also makes the aliens’ Achilles heel in the movie Mars Attacks! kind of ridiculous, since the whole deal was that they could only survive in a nitrogen atmosphere. We have that, Mars doesn’t. Mars is mostly carbon dioxide, but not even much of that. But don’t get me started.

Despite all that, it’s still a fun film.

And Titan, next to Jupiter’s moon Europa, is one of the more likely places we might find life in our solar system.

One final bit of March 25th news in space for this day: In 1979, OV-102, aka Space Shuttle Columbia, was delivered to NASA. It was the first shuttle completed, and its delivery date, after a flight that had begun on March 24th, came four years to the day after fabrication of the fuselage began. Sadly, it was also the last shuttle to not survive its mission, so there was a strange sort of symmetry in that.

While I warned you about the Ides of March, the 25th should be full of nothing but anticipation, even in a plague year. It’s a date for exploration and discovery, whether out into the cosmos, or within the confines of whatever space you’re in right now. Make good with what you have, create all you can, and take advantage of our wonderful technology to share and connect.

After all, that’s what worked for Clavius and Huygens. They worked with the tech they had, then networked once they had an idea, and look how well that worked out.

Hint: It worked out very well, for them and for us.

Image Source: Titan, by NASA.

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