Choose a place, date and time
Choose a city, date and local time. The page shows the Sun's elevation at that moment and the maximum elevation for the corresponding apparent solar date. To compare cities, keep the date and time fixed and change only the place; to compare seasons, keep the place fixed and change only the date. Change one thing at a time to see the difference more clearly.
Solar elevation is the angle between the Sun's direction and the local horizontal plane. It describes where the Sun is in the sky; it is not the UV Index (UVI) or the amount of UV reaching your skin.
How to read the solid and dashed lines
The horizontal axis shows local apparent solar time; the vertical axis shows solar elevation. The solid line means the Sun's center is above the geometric horizon, and the dashed line means it is below. The highest point is the maximum solar elevation for the apparent solar date shown on the chart. Near midnight, that date may differ from the clock date. The 0° line marks the geometric horizon; where the curve crosses it is the model's estimate of when the Sun's center crosses the horizon.
When the Sun's center is below the horizon, the curve is dashed so you can see the full day. The curve does not show twilight or how bright the ground is. Scattered sunlight may still brighten the sky after sunset. If the curve stays below 0° all day, the model indicates the Sun's center did not rise above the geometric horizon that day.
The curve's intersections with 0° are only a geometric reference for sunrise and sunset, not an observation or forecast for your location. Atmospheric refraction, terrain and the actual horizon affect when the Sun appears; the differences may be more noticeable when the Sun is close to the horizon.
Why clock time and apparent solar time differ
The main controls show local clock time. In More settings, you can view or adjust apparent solar time, the time zone and coordinates. Apparent solar time follows the Sun's motion across the sky, so 12:00 apparent solar time is local solar noon and may differ from 12:00 on the clock. Longitude and the equation of time both affect the difference.
When you change the place or time zone, the page keeps the same UTC instant and converts it to local clock time using the new setting. The displayed date or time may change. Changing only the time zone does not change the place; changing the place recalculates the Sun's position.
Change one setting at a time
For example, to compare Beijing and Guangzhou on the same day, keep the date and time fixed and change only the city. To compare Beijing in summer and winter, keep the city fixed and change only the date. The curve shows how the Sun rises and falls, its highest point and the nighttime hours; the globe helps you explore day and night, latitude and seasons.
Solar elevation only shows the Sun's position relative to the horizon; it cannot replace the day's UVI. Clouds, ozone, altitude and surface reflection also affect UV levels. Solar elevation or this curve alone cannot tell you what protection is needed at a particular location.
Check the weather and UVI before heading out
For a walk or another outdoor activity, use the curve to estimate the daylight hours, then check your local hourly weather, temperature and UVI. The World Health Organization recommends protection when the UVI is 3 or higher. Also consider shade along your route and any weather alerts.
If the page shows a seasonal dietary-source reminder, the maximum solar elevation for the local apparent solar date is strictly below 30°. It prompts you to pay attention to food sources of vitamin D. It does not mean vitamin D production in the skin has stopped, and it cannot determine whether someone is deficient, estimate sun-exposure minutes or set a personal protection time.
“Vitamin D made in the skin” means the skin produces vitamin D through UVB exposure; “vitamin D from food” means getting it from food. The two sources complement each other, and it is helpful to keep foods containing vitamin D in mind in everyday meals.
What the 30° seasonal reminder means →
How latitude affects solar elevation →