Undergrad Longest day of the year is June 21 but longest daylight is June 26?

[gary350]

TL;DR

Longest day of the year is June 21 but longest daylight is June 26 ?????

I was reading a NASA web side where I can find angle of the sun and day length at my zip code. Longest day of the year is June 21 for 2 years then June 22 for 2 years, after leap year, longest day is June 21 again for 2 years. I already knew that. Then I see something I never saw before. If longest day is June 21 the longest amount of sunlight is 5 days later June 26. HOW is that possible? Is that a typing error? How can the longest day sun rise to sun set not be the longest amount of sunlight?

 

[hmmm27]

"longest day"(northern hemisphere) and "most sunlight"(entire planet) are unrelated events. One is a result of axial tilt, the other the elliptical orbit around the Sun. [edit: and perihelion is in January so that's not it... @OP got a link ?]

 

[Herman Trivilino]

Daylight arrives before sunrise and lasts after sunset.

 

[Baluncore]

There are many reasons why things are not as simple as they could be.

The date of the June solstice is an instant in the orbit of the Earth about the Sun, it usually falls on June 21 or 22, but for people in local time zones near the dateline it can be just outside that window.

The orbit of the Earth is slightly elliptical, and the solstices and equinoxes are defined by the Earth crossing 0°, 90°, 180° and 270° directions from the Sun to the vernal equinox reference direction, the line where the ecliptic intersects the celestial equator.

Sunrise and sunset are defined by any limb of the Sun being seen above the horizon. The Sun is half a degree across, and it takes four minutes for the Earth to rotate one degree, so the Sun rises on average 1 minute earlier and sets one minute later. The days must average at least 2 minutes longer than the nights. Refraction of sunlight from over the horizon, by the density variation of the atmosphere, increases the visibility, so can extend that longer day significantly.

The equation of time, shows that unexpected things can happen if your zip code is near the tropics. https://en.wikipedia.org/wiki/Equation_of_time
Near the solstice, the time of sunrise, and of sunset, are changing at the greatest rate, but in the same direction. That makes it interesting, if you estimate day length based only on either the time of sunrise or sunset.

So it depends on the exact wording of the statement, and your zip code, as to why there is a difference in the longest day and the solstice.

 

[hutchphd]

TL;DR Summary: Longest day of the year is June 21 but longest daylight is June 26 ?????

I was reading a NASA web side where I can find angle of the sun and day length at my zip code.

Please reference the exact source so we can all view it!