What Is Solar Noon? Why It Doesn’t Always Happen at 12:00 PM
Solar noon is the time when the Sun reaches its highest position in the sky for the day from the observer’s location. Because of its name, it is easy to assume that solar noon always occurs at 12:00 p.m. However, the actual time of solar noon can vary depending on the location’s longitude, time zone, daylight saving time, and the time of year.
Solar noon generally occurs when the Sun crosses the local meridian at the observer’s location. Let’s take a closer look at what the local meridian is and why solar noon does not always occur at exactly 12:00 p.m.
What solar noon means
As mentioned earlier, solar noon refers to a specific time of day. More precisely, it is the moment when the Sun crosses the local meridian at a given location.
From the observer’s perspective, the local meridian is an imaginary line that extends from the northern horizon, passes through the point directly overhead, and continues to the southern horizon. As the Sun appears to move from east to west across the sky during the day, it eventually crosses this line.
The moment the Sun crosses the local meridian is generally when it reaches its highest altitude in the sky for that day. In other words, solar noon is the time when the Sun is at its highest point in the sky from the observer’s location.
Why solar noon is not always 12:00 PM
Solar noon does not always occur at 12:00 p.m. because solar time and clock time are determined in different ways. Solar noon is the moment when the Sun crosses the observer’s local meridian and reaches its highest position in the sky for that day. By contrast, 12:00 p.m. is a clock time based on the standard time adopted across an entire time zone.
Each time zone is based on a standard meridian, but most locations do not lie exactly on that meridian. If an observer is located west of the time zone’s standard meridian, solar noon generally occurs later than 12:00 p.m. If the observer is located east of it, solar noon generally occurs earlier.
For this reason, solar noon often does not occur at exactly 12:00 p.m. Its precise time can also vary throughout the year because of the equation of time.
How Longitude, Time Zones, and Daylight Saving Time Affect Solar Noon
The clock time of solar noon can also vary depending on longitude, time zones, and daylight saving time.
First, longitude affects when the Sun crosses the local meridian. Locations farther east generally experience solar noon earlier, while locations farther west experience it later.
A time zone does not change the astronomical event itself or the actual position of the Sun. Instead, it determines how the time of solar noon is displayed on the local clock. As a result, the same solar event may be shown at different clock times depending on the time zone used at that location.
Daylight saving time also does not change the Sun’s position or the actual moment of solar noon. However, because clocks are moved forward by one hour, the local clock time of solar noon is displayed one hour later. For example, solar noon shown as 12:30 p.m. under standard time would be displayed as 1:30 p.m. during daylight saving time.