The Sun’s arc across the sky determines when sunrise and sunset occur, how long daylight lasts, and the quality of light throughout the day. This path, known as the sun path across the sky, shifts predictably with the seasons due to Earth’s axial tilt of 23.5°. Understanding this motion explains why summer days are long, why winter shadows stretch, and why the Sun never rises due east or sets due west except at equinox.
What Determines the Sun’s Daily Path
The Sun appears to move from east to west because Earth rotates on its axis. But the sun path across the sky also changes north–south over the year. At the June solstice (~June 21), the Sun reaches its highest declination of +23.5°, climbing highest in the sky for locations in the northern hemisphere. By the December solstice (~December 21), it drops to –23.5°, staying low and producing short days. At the equinoxes (~March 20 and ~September 22), the Sun crosses the celestial equator, rising precisely east and setting west.
Three key factors shape the daily arc: - Your latitude: closer to the equator means a higher, more direct path. - The season: the Sun’s declination changes by up to 23.5° north or south. - Time of day: the Sun peaks at solar noon, when it crosses the local meridian.
The geometry is straightforward: the Sun’s altitude at solar noon equals 90° minus your latitude, plus or minus its declination. For example, at 40°N on the June solstice, noon altitude is 90 – 40 + 23.5 = 73.5° above the horizon.
How the Path Changes Through the Year
From the winter solstice to the summer one, the sun path across the sky gains altitude and shifts its rising point northward. At the summer solstice, the Sun rises farthest northeast, sets farthest northwest, and takes the longest route across the sky. Conversely, at the winter solstice, it rises southeast, sets southwest, and traces a short, low arc.
Between solstices, sunrise and sunset points move by about 0.5° per day. This drift is most noticeable near equinox, when sunrise shifts rapidly along the horizon. Our /calendar/ provides exact solar noon and twilight times for any date, helping you track these changes precisely.
In the southern hemisphere, the pattern is mirrored: the December solstice brings high summer sun, while June brings low winter arc. You can see this contrast explained at /sydney/.
Twilight and the Sun’s Position Below the Horizon
Twilight occurs before sunrise and after sunset, when the Sun is just below the horizon. Its duration depends on how steeply the sun path across the sky descends. Astronomers define three twilight phases: - Civil twilight: Sun 0–6° below horizon. Enough light for outdoor activities. - Nautical twilight: Sun 6–12° below. Horizon is still visible at sea. - Astronomical twilight: Sun 12–18° below. Sky dark enough for faint stars.
At high latitudes, twilight can last hours because the Sun’s path dips shallowly. Near the equator, twilight passes quickly—the Sun drops almost vertically, so civil twilight lasts only about 20 minutes. The angle of the Sun’s path also affects golden hour, when warm light bathes the landscape; we cover the exact solar altitudes for that at /blog/what-is-golden-hour.
The Relationship Between Path and Daylight Duration
The length of daylight depends entirely on the sun path across the sky—specifically, the time between sunrise and sunset. At the equator, day length stays near 12 hours year-round because the Sun’s path is steep and consistent. At 50°N (southern UK, northern France), summer solstice yields roughly 16 hours of daylight; winter solstice gives barely 8 hours.
This variation follows simple trigonometry: the Sun rises when its hour angle equals the arccosine of (–tan φ × tan δ), where φ is your latitude and δ is the Sun’s declination. For example, at 45°N on the June solstice (δ=+23.5°), the Sun rises at an hour angle of about 111°, meaning sunrise occurs 7.4 hours before noon—so total daylight is 14.8 hours.
Our /blog/how-latitude-affects-daylight explores deeper how the Sun’s arc changes with geography, from polar midnight sun to equatorial constant daylight.
Why the Sun’s Path Affects Solar Energy and Shadow Length
The height of the sun path across the sky directly influences solar radiation intensity. When the Sun is high (summer noon), its rays pass through less atmosphere, delivering more energy per square metre. When low (winter noon), the same energy spreads over a larger area, reducing power density.
Shadow length is a visible result. At solar noon in summer, a metre-high post casts a short shadow—perhaps 30 cm at 50°N. In winter, that same shadow stretches several metres. The formula is simple: shadow length = object height / tan(solar altitude). So at 20° altitude, a 1 m post casts a 2.75 m shadow.
Smart solar panel orientation—tilting panels to match the Sun’s average noon height—maximises yearly yield. That tilt equals the location’s latitude, because at equinox the Sun’s noon altitude is 90° minus latitude.
Wrap-Up
The Sun’s daily arc is not random: it follows a precise, predictable path governed by Earth’s tilt and orbit. By understanding how that sun path across the sky shifts with latitude and season, you can anticipate daylight, plan photography, or design energy systems. For accurate local times and angles any day of the year, check our /calendar/ with daily sun data tailored to your location.
Related reading on Sunrise.am: daily sun data, the Sun's path in the southern hemisphere, latitude and the Sun, golden hour angles.