Editor’s be aware: Dr. William Teets is the director of Vanderbilt College’s Dyer Observatory. On this interview, he explains what does and doesn’t occur in the course of the winter solstice on Dec. 21. One other cosmic phenomenon can also be going to happen on the identical day known as “the nice conjunction,” the place Saturn and Jupiter, each of which will be seen with the bare eye, will seem extraordinarily shut to at least one one other.

What occurs on the winter solstice?

The winter solstice this yr occurs on Dec. 21. That is when the Solar seems the bottom within the Northern Hemisphere sky and is at its farthest southern level over Earth – instantly over the Tropic of Capricorn. For people dwelling at 23.5 levels south latitude, not solely does today mark their summer season solstice, however additionally they see the Solar instantly over them at native midday. After that, the Solar will begin to creep again north once more.

The sequence of photographs beneath exhibits the trail of the Solar by way of the sky at completely different occasions of the yr. You may see how the Solar is highest within the Northern Hemisphere sky in June, lowest in December, and midway in between these positions in March and September in the course of the equinoxes.

The winter solstice is the shortest day within the Northern Hemisphere however not the day with the most recent dawn and earliest sundown. How is that attainable?

The winter solstice doesn’t coincide with the most recent dawn or the earliest sundown. These really happen about two weeks earlier than and two weeks after the winter solstice. It is because we’re altering our distance from the solar resulting from our elliptical, not round, orbit, which modifications the velocity at which we orbit.

In case you had been to take a look at the place the Solar is at precisely the identical time of day over completely different days of the yr, you’d see that it’s not all the time in the identical spot. Sure, the Solar is greater in the summertime and decrease within the winter, however it additionally strikes back and forth of the typical noontime place, which additionally performs a job in when the Solar rises and units.

One must also understand that the seasons are because of the Earth’s axial tilt, not our distance from the Solar. Imagine it or not, we’re closest to the Solar in January.

{A photograph} of the place of the Solar, taken on the similar time on completely different days all year long, exhibits a figure-eight sample often called an analemma. This photograph was taken in Callanish, Scotland.

Giuseppe Petricca, NASA

What’s ‘the nice conjunction’?

Saturn and Jupiter have appeared pretty shut collectively in our sky all year long. However on Dec. 21, Saturn and Jupiter will seem so shut collectively that some of us could have a tough time seeing them as two objects.

In case you have a pair of binoculars, you’ll simply have the ability to spot each planets. In even a small telescope, you’d see each planets on the similar time in the identical discipline of view, which is basically extraordinary. That’s what makes this conjunction so uncommon. Jupiter and Saturn seem to satisfy up about each 20 years. More often than not, nonetheless, they’re not practically as shut collectively as we’re going to see them on Monday, Dec. 21.

For a comparability, there was a terrific conjunction again in 2000, however the two planets had been separated by about two full-Moon widths. This yr, the orbits will convey them to the place they seem like about one-fifth of a full-Moon diameter.

We’ve got been encouraging of us to exit and have a look at these planets utilizing simply their eyes between now and Dec. 21. You’ll really have the ability to see how a lot they seem to maneuver over the course of a single day.

The subsequent time they may get this shut collectively in our sky gained’t be for one more 60 years, so that is going to be a once-in-a-lifetime occasion for many individuals. In actual fact, the final time they received this shut collectively was within the yr 1623, however it was actually tough, if not unimaginable, to see them then as a result of they appeared a lot nearer to the Solar and set quickly after it. Return one other 400 years to 1226 and this is able to have been the final time that we’d have had a superb view of this sort of conjunction.

What recommendation would you give to individuals who need to see the nice conjunction?

If climate permits at Dyer Observatory, we’ll be streaming a reside view of the conjunction from one of many observatory’s telescopes, and I’ll be accessible to reply questions. Even if you happen to don’t have a telescope or a pair of binoculars, undoubtedly exit and take a look at this very uncommon alignment with your individual eyes. Keep in mind that they set quickly after sundown, so be able to view proper at nightfall!

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William Teets doesn’t work for, seek the advice of, personal shares in or obtain funding from any firm or organisation that might profit from this text, and has disclosed no related affiliations past their educational appointment.