Busy day on the solstice this year [updated with APOD link]

The December solstice, shortest day of the year is tomorrow, December 21. At approximately 7:38 p.m. EST (2338 UTC), the Sun’s apparent motion in the sky will come to a standstill (Latin, solstitium).* That’s because it has finished its southward migration for the year, and from here until June old Sol will travel north. And as it does so, days in the northern hemisphere will get longer. The image below, from an excellent NASA website, shows the paths of the sun on the longest and shortest days of the year:

The apparent path of the Sun across the […]

Full moon and equinox

Two images of last night’s full moon appear below. One was taken a few minutes before the equinox; the other was taken a few seconds after it. Can you tell which is which? (Hint: the moment at which the equinox occurs has no bearing on the appearance of the moon.)

At the time these pictures were taken, the sun was on the opposite side of the earth. The moon was about 6 hours shy of full (which occurred officially at 5:18 a.m. EDT this morning), but close enough that it would take a trained eye to […]

June solstice, or, the longest day

Today is the June solstice. That means that today, at 7:28 a.m. EDT, the Sun’s apparent motion in the sky will stop moving north, and start heading south. This is because we are at that point in our orbit around the Sun where the following image takes place:

Earth's rotation axis relative to our orbital plane (image from NASA, http://www-istp.gsfc.nasa.gov/stargaze/Sseason.htm)

As you can see, the northern hemisphere is receiving the majority of the Sun’s rays today. The further south you go, the shorter your day length will be, as this comparison between Boston and Boca Raton illustrates:

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December solstice, or the shortest day

The December solstice, shortest day of the year is today, December 21. At approximately 12:47 p.m. EST (1747 UTC), the Sun’s apparent motion in the sky will come to a standstill (Latin, solstitium).* That’s because it has finished its southward migration for the year, and from here until June old Sol will travel north. And as it does so, days in the northern hemisphere will get longer. The image below, from an excellent NASA website, shows the paths of the sun on the longest and shortest days of the year:

The apparent path of the Sun across the […]