Solar Time vs Clock Time Calculator
Convert standard clock time to true solar time for any location and date. Useful for astronomers, sundial builders, and anyone tracking solar noon or sunrise/sunset times precisely.
Last updated: October 2026
Solar Time
12.04 hours
Formula below · 2 sources (gml.noaa.gov, midcdmz.nrel.gov) · Updated Oct 2026
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About this calculator
Solar time is clock time corrected for how far you are from your time zone's central meridian and for the equation of time: in New York (74.0° W) at 12:00 Eastern Standard Time (UTC−5) on June 21, the sun is at about 12:03 solar time, so solar noon comes about 3 minutes before 12:00 EST, which is 1:00 pm on daylight saving clocks. Solar noon, when the sun is highest, is 12:00 solar time.
Longitude correction
Each time zone is centered on a meridian that is a multiple of 15° (UTC−5 is centered on 75° W), and the sun crosses 1° of longitude every 4 minutes. A place east of its zone meridian sees the sun early; a place west of it sees the sun late. New York is 1° east of 75° W, so its sun runs about 4 minutes ahead of the zone.
Equation of time
Because Earth's orbit is elliptical and its axis is tilted, the sun runs up to about 16 minutes ahead of mean time in early November and about 14 minutes behind in mid-February. The calculator uses EoT = 9.87 sin 2B − 7.53 cos B − 1.5 sin B minutes, with B = 2π(day − 81)/365, which tracks NOAA's more detailed formula to within about a minute. The table below gives NOAA values for selected dates.
The formula
Solar time = clock time + (longitude ÷ 15 − UTC offset) + EoT ÷ 60, in hours, with longitude negative west of Greenwich. If your clocks are on daylight saving time, enter the offset in use (UTC−4 for New York in summer), or the result will be an hour off. The result is shown as decimal hours: 12.04 means about 12:03.
| Date | Equation of time (min) | Sun vs. clock | Solar noon on the zone meridian |
|---|---|---|---|
| Jan 1 | −2.9 | Behind | 12:03 |
| Feb 11 | −14.2 | Behind (near maximum) | 12:14 |
| Apr 15 | −0.2 | About even | 12:00 |
| May 14 | +3.9 | Ahead | 11:56 |
| Jun 13 | +0.4 | About even | 12:00 |
| Jul 26 | −6.6 | Behind | 12:07 |
| Sep 1 | −0.4 | About even | 12:00 |
| Nov 3 | +16.4 | Ahead (maximum) | 11:44 |
| Dec 25 | +0.3 | About even | 12:00 |
How to use
Enter your longitude (negative west of Greenwich), your current UTC offset in hours (including daylight saving time if it is in effect), the day of the year and the clock time. The default, New York (−74.006°) at 12:00 standard time (UTC−5) on day 172 (June 21), returns about 12.04 hours, or about 12:03 solar time. On daylight saving time, enter −4 instead. To find the clock time of solar noon, change the clock time until the result reads 12.00, or subtract the difference from 12:00.
Frequently asked questions
Why is solar noon not at 12:00 on the clock?
Two reasons. Time zones are about 15° wide, so most places are east or west of their zone's central meridian, which shifts solar noon by 4 minutes per degree. The equation of time then adds up to about 16 minutes either way through the year. Daylight saving time shifts it a further hour.
What is the equation of time?
It is the difference between apparent solar time, read from a sundial, and mean solar time, kept by clocks. It comes from Earth's elliptical orbit and axial tilt. The sun is about 14 minutes behind mean time in mid-February and about 16 minutes ahead in early November, and the difference passes through zero four times a year.
How do I find the exact time of solar noon?
Solar noon on the clock = 12:00 − (longitude ÷ 15 − UTC offset) hours − equation of time. With this calculator, set the clock time to 12:00 and read the result: if it shows 12.04, the sun peaked about 3 minutes earlier, at about 11:57. NOAA's solar calculator also lists solar noon for any location and date.
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