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January 02, 2021 Log In Sign Up HODINKEE Logo [comments-b] * * * * In-Depth The Eerie Beauty Of The Apple Watch Solar Face, And The Anatomy Of Nightfall [2020_Year_] In the Shop Year In Review The 2020 HODINKEE Shop Round-Up [Rapport_Wa] In the Shop Shop Spotlight The Dos And Don'ts Of Watch Winders [loreta-pav] Weekend Round-Up Tennis Champs, Eco-Yogis, And Yacht Hunting In-Depth The Eerie Beauty Of The Apple Watch Solar Face, And The Anatomy Of Nightfall Welcome to the Twilight Zone. [jack_forst] Jack Forster April 08, 2020 * * * * [comments-b] --------------------------------------------------------------------- ADVERTISEMENT --------------------------------------------------------------------- Editors' Picks 1. In-Depth Everything You Need To Know About The Rolex Explorer Ref. 14270 2. Talking Watches With Todd Levin 3. Reference Points Understanding The Rolex GMT-Master ADVERTISEMENT There were 10 basic Apple Watch faces when the Apple Watch launched in 2014, and since then, the number has increased significantly, to put it mildly. Today, there are 31 groups of faces, which range from Activity to X-Large, and if you include all the variations in each group and then add in all the possible permutations of colors and complications, you get a total which is, if not too many to count, certainly laborious to calculate. Indeed, if you like the Apple Watch at all, you can probably find almost anything to suit your mood or a change of taste (and if you want to add in the number of different experiences you can create with all the possible strap variations, the number becomes truly astronomical). My personal favorites have always included some of the astronomically oriented Apple Watch faces, including the planetarium face (which lets you see the positions of all the planets past, present, and future by turning the crown). The original version of the Solar face was the Solar Graph, which shows the Sun's elevation in the sky, as well as the time of sunrise, solar noon, sunset, twilight, and nightfall proper. Solar noon is of interest as it is the moment when the Sun is actually at its zenith, which is generally not at noon on the clock. This is due to the fact that civil time is the time across an entire time zone, and the problem is worsened in parts of the world that observe daylight saving time. [3S3A9136] The Solar Dial, launched with the Apple Watch Series 5. As of WatchOS 6, which was introduced last September, there is a new Solar watch face. This one is simply called the Solar Dial, and it is a remarkably charming thing. It has been described as a miniature sundial for the wrist, but it is rather more like having a sundial and the Sun itself on your wrist, both at the same time. Moreover, it bears a certain resemblance to some rather exotic complications found in mechanical watches, about which more later. The Solar Dial consists of a 24-hour dial with 12 (noon) at the top and 24 (midnight) at the bottom. An hour hand moves once around the dial per day, and attached to the hour hand is miniature representation of the Sun. The portion of the dial that's in light blue represents the number of daylight hours, and the portion in dark blue, night; the boundaries between each section mark sunrise and sunset. Opposite the Sun on the 24-hour hand is a smaller dial which shows the hours and minutes, in either an analog or digital format. The four corners of the watch face are taken up with customizable complications (in my case, from the upper left clockwise: world time, date, activity tracker, and workout). [729A5452] Tapping the Solar Dial watch face will allow you to see whether it's day, or night, or one of the various phases of twilight. You can also see how many hours of daylight there are. The color of the sky also changes depending on the time of day, and during the twilight hours, you get a very pretty transition from blue, to a deeper blue, to a lovely pale pink as the solar disk begins to sink below the horizon. You can rotate the crown to show you what time sunset takes place, as well as the various phases of twilight. You'll also see, in yellow numbers in the sub-dial, how many hours it is from the current time to sunset, or other solar astronomical events. [IMG_4869] You'll also notice that for both dawn and sunset, there are a total of four small dots spanning the period of time during which the sky goes from sunlit to completely dark. Above, the 24-hour hand and Sun disk are at Sunset. Sunset is very specifically defined, as is sunrise: They are the moments when the upper limb (edge) of the Sun's disk disappears below, or appears above, the horizon. (The precise definition is the moment when the edge of the upper limb is tangent to the horizon line). Interestingly enough, because of the refraction of the Sun's image in the Earth's atmosphere, at the moment of visible sunset from an observer's position, the Sun is actually already just slightly more than one solar diameter below the horizon. ADVERTISEMENT However, the disappearance of the Sun's upper limb below the horizon does not mean night falls instantly, like someone shutting off a light switch. Instead, it is the beginning of a period called twilight. Twilight is the period between sunset and true nightfall, when the last bit of sunlight finally vanishes, and the sky becomes completely dark. Twilight, as it turns out, is further divided into three phases: Civil Twilight, Nautical Twilight, and Astronomical Twilight, and it is the phases of twilight, plus sunset, which are indicated by the four dots clustered at sundown. As each type of twilight darkens, it reaches its Dusk phase, which marks the transition into the next Twilight period. (The word twilight, incidentally, is Old English in origin ... appropriately enough for a term describing visual obscurity, it is unclear what the prefix "twi" actually means; the word may mean, "half light.") In order, therefore, the sequence starting at Sunset is: Sunset, Civil Twilight, Civil Dusk; Nautical Twilight, Nautical Dusk; Astronomical Twilight; Astronomical Dusk ... and finally, Night proper. This is followed by Solar Midnight, which is the moment when the Sun is at its nadir on the celestial sphere from the standpoint of the observer. [Twilight_s] Day, Night, and what comes in between. Graphic, T. W. Carlson. Particularly in the days before ubiquitous nocturnal electrical lights, experiencing the fall of night must have been a source of anxiety - you can only light so many candles, and the fading of light from the sky must have always had a faint miasma of death about it. The civilized person in us is sure the Sun will come up again, but in our animal hearts, we are perhaps less certain. Shakespeare captured the irrational mood of the hours of darkness well in that darkest of plays, Hamlet, with the titular character's soliloquy: "Tis now the very witching time of night, When churchyards yawn and hell itself breathes out Contagion to this world: now could I drink hot blood, And do such bitter business as the day Would quake to look on." Twilight has its own rich vocabulary, including the word crepuscular; "that which is related to twilight." Animals that are chiefly active during the twilight of dawn or nightfall are called crepuscular animals; my favorite of these, and maybe yours too, is the firefly. ADVERTISEMENT --------------------------------------------------------------------- Civil Twilight Of the three Twilights - Civil, Nautical, and Astronomical - it is Civil Twilight which seems to have the most nebulous history (to make a feeble joke). Civil Twilight seems to have been defined fairly recently, historically speaking; the term is not attested in English until 1817, when Thomas Leybourn wrote, "All these notions are extremely vague, and refer less to the astronomical twilight, than to that other twilight which allows to labour and to read, which was first mentioned by Lambert, and named by him civil twilight." Leybourn was referring to the Swiss mathematician and physicist, Johann Heinrich Lambert, who died at 49 in Prussia in 1777 and who is famous for, among other things, the first proof that p is irrational. [IMG_5184] Civil Twilight begins immediately at sunset. Merriam-Webster has a lovely short essay on the history of the concept of Civil Twilight, which mentions that as recently as the early 20th century, there were at least six different definitions of it. Practically speaking, the definition of Civil Twilight had less to do with astronomy, and more to do with defining how late in the day work could be done, indoors or out, without resorting to artificial light. [IMG_4879] Civil Dusk is the last and darkest phase of Civil Twilight. The accepted definition of Civil Twilight today is that it begins at Sunset (which by definition is an instantaneous moment in time) and that it lasts until the geometric center of the Sun is 6o below the horizon. Civil Twilight is not only an astronomical event - it is also important in fields as diverse as aviation and law. Here in the United States, the FAA defines night, and the additional regulations pertaining to nighttime aircraft operations, as the period between the end of Civil Twilight and the beginning of morning Civil Twilight. Civil twilight is also used in some jurisdictions to determine whether or not a crime has been committed at night or not, as the penalties for nocturnal malfeasances may be more severe than those committed during the day. (One wonders what the rationale for this might be. Certainly, the distinction is unlikely to matter to the victim of a burglary - perhaps the view is that in operating at night, the criminal is somehow cheating, or demonstrating a lack of nerve, and therefore more morally culpable?) --------------------------------------------------------------------- Nautical Twilight The second of the three Twilights is Nautical Twilight, and as you might imagine from the name, it is of special relevance to mariners. Nautical Twilight begins at the exact moment that Civil Twilight/Dusk ends, when the geometric center of the Sun is 6o below the horizon. [IMG_4870] Nautical Twilight: stars begin to appear, horizon still visible. The term "Nautical" in Nautical Twilight gives a clue as to what it means from an observational standpoint. For celestial navigation, one of the numbers you need is the elevation of a celestial body above the horizon, particularly well-known reference stars. Nautical Twilight is the period during which it starts to get dark enough that such stars begin to become visible in the sky, but also during which there is still enough residual light in the sky for the horizon line to be visible. [IMG_4876] Nautical dusk: horizon becomes invisible, navigational observations no longer possible. This is something I had never particularly considered about celestial navigation, but of course, if what you need to navigate is the azimuth and altitude of a star, and you're using the horizon as a reference, you actually don't have all that much time in which to work as it has to be dark enough for the star in question to be visible, but not so dark that you can't see the horizon anymore. As you get closer and closer to Nautical Dusk, it gets harder and harder to make out the horizon and eventually it becomes impossible. Modern sextants (the navigational instrument used for measuring celestial altitudes) often incorporate an artificial horizon, which allows you to take sightings even when the horizon can't be seen. Nautical Twilight ends when the Sun's geometric center is 12o below the horizon - that is the actual moment of Nautical Dusk and the beginning of Astronomical Twilight. Nautical Dusk and Dawn were, historically, the moments when military operations had to halt and defensive positions assumed, or when operations could commence, as those moments were when available light had fallen below the minimum needed to engage the enemy, or had increased to the point that maneuver was possible. ADVERTISEMENT --------------------------------------------------------------------- Astronomical Twilight Astronomical Twilight begins when the Sun's geometric center is 12o below the horizon and ends when it reaches 18o below the horizon. [IMG_4882] Astronomical Twilight is perhaps the most poetic of the three from an experiential standpoint - it's the period when the stars really come out. While Civil Twilight and Nautical Twilight are both driven, definitionally, by practical considerations (how late you can work, and the requirements of celestial navigation, respectively) astronomical twilight is based purely on celestial observation. I suppose if it has a practical consideration, it is only to naked-eye astronomers, and of all the sciences, I have always found astronomy to be the most reassuringly abstract. Certainly, it does not produce the sort of we-never-stopped-to-think-if-we-should moments that you get with things like genetics or nuclear physics. The moment in which astronomical twilight begins is at Nautical Dusk, when the geometric center of the solar disk is 12o below the horizon, and it ends at true nightfall, when the geometric center of the solar disk reaches 18o below the horizon. During this period, the faintest stars visible to the naked eye become gradually visible (6th magnitude). Unfortunately, those of us who live in large cities generally don't have an opportunity to experience Astronomical Twilight, thanks to light pollution. There are also three twilights associated with the morning hours, which go by the same names - Astronomical Twilight, Nautical Twilight, and Civil Twilight - which begin when the Sun is 18o below the horizon and which end at dawn. The Solar Dial also shows the moment of true Solar Noon and true Solar Midnight, which represent the zenith and nadir of the Sun's position in the sky, respectively. [IMG_4884] --------------------------------------------------------------------- A Challenge To The Watchmakers A complaint that I often hear about the Apple Watch is that "it is not really a watch," (which sometimes seems to me a way of saying, "I don't like smartwatches and I reject them as utterly irrelevant to what makes a watch enjoyable, relevant, and ethically and morally defensible"). For me, one of the most interesting things about the Apple Watch is that you can have lots of different experiences depending on how you customize the various faces and depending on which one you choose to spend time with. I think the Solar Dial creates a very watch-like experience - perhaps more than any of the other dials. However, as a fan of astronomical complications, I can't help but wonder if this sort of complication couldn't be realized in a mechanical wristwatch or pocket watch. A "Three Twilights" watch would be a wonderful thing - we already have sunrise and sunset complications, and there are watches which show the moment of true solar noon as well. One of these is the out-of-production but very much lamented (by me, anyway) Jules Audemars Equation Of Time - a stunning complicated timepiece that will wash the taste of Royal Oaks out of your mouth like nothing else. It shows the time of sunrise and sunset, as well as true solar noon and the Equation of Time, and it is a perpetual calendar to boot. [AP_JA_EOT] I haven't actually dug deep enough to find out if you could drive a Three Twilights complication directly off a sunrise-sunset complication, but there are a couple of watches that point in that direction, including the Krayon Everywhere watch and the Ochs Und Junior Day/Night. Both use systems of moveable fan-like shutters to show whether the Sun is above or below the horizon, and they bear a family resemblance to how the position of the Sun is shown in the Apple Watch Solar Dial. Since the duration of the Twilights is based on geometry, it seems to me that at least theoretically, it might not be too difficult to engineer such a complication (which would, like the sunrise/sunset complication itself, probably need to be made for a specific location). [Untitled_S] The Ochs Und Junior Day/Night watches. [P3251508] The Krayon Everywhere watch, which can show sunrise/sunset times almost anywhere in the world. Such a thing would be enormously charming, and it would be if not completely new, at least a most interesting new variation on the sunrise/sunset complication. But, for now, I give the Apple Watch Solar Dial a lot of credit for taking the properties of the smartwatch and using them to create a very captivating experience. The luminosity of the display and its ability, as night falls or sunrise dawns, to display different colors, as well as the general composition of the dial, makes for something much richer and far more emotionally evocative than the mere delivery of information. And too, it gives us a chance to reflect on what darkness and light have meant, and continue to mean, culturally and historically. There is something irresistibly compelling about having a little model universe on your wrist. 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