Spring returns with a not-so-equal vernal equinox of 2021

Space.com ^ | 03202021 | Joe Rao

[outofsalt]

"Spring... arrive(d) on Saturday morning (March 20) with the occurrence of the vernal equinox.

That occurs when the sun will be positioned directly over the Earth's equator at 09:37 Universal Time; 5:37 a.m. Eastern Daylight Time or 2:37 a.m. Pacific Daylight Time." snip "Every year around this time, almost like clockwork, I will get an email from someone who was studying the weather page of his or her newspaper, looking at the section listing the times of sunrise and sunset and noticing that something appears to be wrong."

[outofsalt]

"One factor is that the moments of sunrise and sunset are considered when the top of the sun, and not its center, is on the horizon. This alone would make the time of sunrise and sunset a little more than 12 hours apart on these days. The sun's apparent diameter is roughly equal to half a degree." "But the main reason that this happens can be attributed to our atmosphere; it acts like a lens and refracts (bends) its light above the edge of the horizon." "when you watch the sun either coming up above the horizon at sunrise or going down below the horizon at sunset, you are actually looking at an illusion – the sun is not really there, but actually is below the horizon.

[outofsalt]

Happy technical first day of Spring!

[moovova]

32° (maybe less) here last night. My wx app said 32/27 overnight...so, who knows.

[Nateman]

Did you know a year is not the time it takes to orbit the sun? It is slightly shorter due to the Earth’s Precession of the poles. The actual year is based on where we see the sun return to the same position as it did the last year.

[outofsalt]

Hibernate a little longer, FRiend.

[rellic]

IIRC that is referred to as “Airmass”
at the summit of Mauna Kea that was 13.8
for the Keck Telescopes.

[outofsalt]

Approximately 365.25 days in a year, hence leap years.
The next one is 2024. Even that is not exactly accurate.

[proud American in Canada]

You, too, FRiend!

[moovova]

Hah...I wish! I’ll be out cutting the grass, cleaning the flower beds and spreading pine needles today. Somebody forgot to tell my yard it was freezing last night.

[outofsalt]

[proud American in Canada]

Right. This year, Slow Joe came out of his basement and saw his shadow so there were six more weeks of winter.

And the shadow is made of all the lies, corruption and theft of an election. He couldn’t take it and scrambled back in.

[outofsalt]

Shadow..? Maybe. He doesn’t have a reflection in a mirror.

[proud American in Canada]

#11 was meant for you too. :)

[Nateman]

That huge earthquake in the Pacific that killed so many recently with a tsunami actually changed the length of a day ever so slightly.

[moovova]

LOL!

[Deo volente]

Approximately 365.25 days in a year, hence leap years. The next one is 2024. Even that is not exactly accurate.

That's right. It has to be adjusted by making every century year a leap year only if it's divisible by 400 without a remainder. So 2000 was a leap year, but 2100, 2200, and 2300 will not be.

[buckalfa]

https://m.youtube.com/watch?v=_zfgoJzOCgg

The time has come today?

[nevergore]

"That huge earthquake in the Pacific that killed so many recently with a tsunami actually changed the length of a day ever so slightly."

LOL, Didn't it also tilt Guam?

[PGalt]

https://m.youtube.com/watch?v=GYQfWJNWe3I

Enjoy

😎

[Lonesome in Massachussets]

An interesting pedantic footnote. The article says that the “vernal equinox” is when the sun crosses the equator from the southern hemisphere to the northern hemisphere. This is not quite technically correct. The definition of the vernal equinox is when the geocentric ecliptic longitude of the apparent sun (accounting for light time, but not the effect of stellar aberration) is 0 degrees. According to the JPL, that event occurs just a tad before 09:37:30 UT today. However the sun will not cross equator until shortly after 16:31:58.

According to the same source, the center of the “astrometric” (no refraction) sun rose at the Greenwich observatory at 06:08 UT this morning and will set at 18:08 this evening. The corresponding times for the apparent sun (accounting for refraction) are 6:01 and 18:16, indicating a 15 minute difference due to refraction.

https://ssd.jpl.nasa.gov/horizons