Getting On True Time
Before man had clocks, the sun was his only way of measuring time. Up until as recently as 150 years ago, when the railroads necessitated the introduction of time zones, noon in every town was simply when the sun was at its daily peak. Our bodies respond to sunlight, not the readout of a digital clock. Becoming attuned to the sun's position can help you find your natural rhythm, and being aware of seasonal changes will help you maximize the best uses of sunlight in your life.
Daily Events
There are four events that the sun passes through each solar day. These are defined as follows for the purposes of this app.
Sunrise
The moment when the middle of the sun's visible disc climbs above the horizon.
Solar Noon
The moment when the sun is at its highest point in the sky. Noon on a standard clock differs from solar noon because of time zones and daylight saving (summer) time.
Sunset
The moment when the middle of the sun's visible disc drops below the horizon.
Solar Midnight
The moment when the sun is at its lowest point below the horizon. It is twelve hours from solar noon. During midnight sun, solar midnight, sunrise and sunset are all at the same moment.
Periods of the Day
Generally we think of it being day or night. But there are also several transitional times of day between night and day where you are getting refracted sunlight because of the sun's proximity to the horizon, where the atmosphere can bend the light like a lens or a prism, providing you with beautiful light in the morning, a spectacular sunset, or even enough light to see by a half hour or so before sunrise.
The Golden Hour (or "Magic Hour")
The Golden Hour (also known as the "Magic Hour") is not literally an hour, but the time just after sunrise and just before sunset when the sun is close to the horizon and the atmosphere refracts its rays to produce a more gentle, pleasing, sometimes golden light, especially favored by photographers. For this app, we've set it to be within 10° above the horizon but you can change that in the settings.
Twilight (Dawn and Dusk) Periods:
In general twilight is the period between maximum darkness and sunrise/sunset, where the refracted sunlight lights up the sky providing reduced light. Because there are different ways of measuring darkness, and different uses for this measurement, there are three kinds of twilight: Astronomical Twilight, which is the longest and most scientific, Nautical Twilight, which is a bit shorter, and Civil Twilight, which is the shortest and generally fine for everyday use.
Civil Twilight (or "Blue Hour")
The period just before sunrise (also known as dawn) and just after sunset (dusk) where there is typically still enough natural light to recognize objects. Technically: when sun is between 6° and 0° below the horizon. This is also known as the "Blue Hour" to photographers and "L'heure bleue" to artists.
Nautical Twilight
Quite a bit darker than civil twilight; the period before dawn in the morning, and after dusk in the evening, when the sun is between 12° and 6° below the horizon. It gets its name from being just dark enough for sailors to take reliable readings of stars and the horizon.
Astronomical Twilight
The darkest period of twilight where the faintest stars are still not quite visible to the eye. It is the first period of twilight in the morning and the last in the evening, when the sun is between 18° and 12° below the horizon. Astronomical twilight is as close to night as any of these periods, and most people would consider it full night; except perhaps astronomers who might need the total absence of refracted sunlight to peer into the deepest reaches of the heavens.
Sun's Position
The sun's apparent position relative to a location on earth can be expressed with two angular measures: elevation (or altitude) and azimuth.
Elevation
The height of the sun in the sky, where 0˚ is at the horizon and 90° is directly above. Solar noon occurs when the sun reaches its apex for that day, which is the point at which its elevation is highest. The summer solstice occurs on the day when the sun reaches the highest apex, and the elevation is closest to 90°.
Azimuth
The position of the sun on the compass dial—where north is 0°, east is 90°, south is 180°, and west is 270°— when precision finer than ordinal directions such as east south-east is needed. The sun begins its day at the most easterly point on the compass and moves to its most westerly point. Unless you are on the equator, these will not be true east (90˚) and west (270˚).
Annual Events
The earth makes a trip around the sun approximately every 365 days. Because the earth's axis is on a tilt, the Northern Hemisphere gets more sun exposure and longer days for half of the year (April–September), while the Southern Hemisphere is experiencing more darkness (and shorter days). The opposite is true for the other half of the year. As the days get longer in one hemisphere, they get shorter in the other.
Equinox
There are two days a year when both hemispheres get equal exposure, and both have a 12-hour day and 12-hour night. These days also traditionally signify the beginning of spring and autumn. The Spring Equinox happens in March in the Northern Hemisphere, and in September in the South. Similarly, The Autumn Equinox occurs in September in the North, and in March in the South.
Solstice
There are also two days a year when the earth's axis is oriented at its most extreme with position to the sun, and as a result every place on the planet is having either its longest or shortest day, depending on which side of the equator it's on. The Winter Solstice is the shortest day of the year, and it happens in December in the Northern Hemisphere, and June in the South. The Summmer Solstice is the longest day of the year, and it occurs in June in the North and December in the South.
