This Holiday, Dance With The Stars
Christmas began with a star. From Matthew 2:9: "And, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was." The celestial spectacles of the holiday season continue in December 2024.
With the nights longest near the December 21 solstice, now is a great time to look up. Planets are conveniently spread across the evening sky, stars are spectacular in the cool air, and a rare anticipated nova is ready to burst upon the scene in the morning.
Planets
As 2024 segues into 2025, bright planets dominate the silence. At sunset, brilliant Venus beams unmistakably in the west. A closer look in a telescope shows it's actually half-illuminated, akin to a first quarter moon. Venus having phases is among the key observations Galileo made confirming the planets orbit around the sun. Like with the moon, the only way to have phases is if the object passes between the sun and earth. Be Galileo and marvel anew at what the sky reveals.
While social media hypesters may proclaim the planets are aligning, in fact the planets and the sun and the moon are always found along a line called the ecliptic. It's like looking out from the center hole of a vinyl record at named motes of dust within successive grooves on the flat disc of the solar system, with the ecliptic being the tilted edge of the record seen edge-on.
Saturn is visible as a golden dot to the naked eye, but a small telescope again reveals hidden treasure--a spectacular flat ring around its girth. By 7 PM ruddy Mars is rising in the west. Meanwhile, on Christmas morning, Mercury is at westernmost elongation, seen 22.0° from the sun in the morning sky at magnitude= -0.3.
Moving past (east of) the giants Neptune and Uranus (faint because of their distance despite their massive sizes) you can find the other beacon of the night--mighty Jupiter. A favorite target in binoculars or a telescope, its four largest moons change their respective positions astride Jupiter from night to night. Look at a magnified Jupiter early in the evening, and several hours later you can actually discern the motion of inner moon Io.
Sometimes you'll see fewer than four moons, with the missing brethren hidden behind or in front of the gas giant. Jupiter having orbiting moons is another key observation of Galileo because it showed something(s) orbited Jupiter; therefore, earth was not the immutable center of everything. The night is not as static as it first appears.
Moon
The full moon on December 15 rises and sets at its most northern location in over 18 years, a "major lunar standstill." The familiar beacon rises about 50 minutes later each successive night as it concurrently wanes after the extreme event. It closes out 2024 as a new moon on December 30, not seen because it is nearly in line with the setting sun. By January 2, 2025, a thin crescent becomes visible in the western twilight, growing larger as it moves about 15 degrees east along the ecliptic each day.
On the morning of December 18 the moon, Mars, and the Beehive cluster are nearly all within a 3-degree circle. On December 28 the moon buzzes past the red giant star Antares, known as the "rival of Mars" in color and brightness. Closing out the year, on December 30 the new moon begins lunation 1262. Who cares what that means--just call it another reason to celebrate the holidays.
Stars
The whole sky is in motion. To the north, stars circumnavigate Polaris. Looking south, as the earth rotates to the left you see the starfield slowly shift to the right. The individual specks of light appear to rise and set, though they are merely sweeping out giant circles just like the circumpolar stars do, except the earth keeps getting in the way.
Of course, even Santa depends on the stars to navigate through his big night. A simple Santa's Favorite Stars activity reveals the constancy of both the diurnal and annual motions.
And let's give Santa credit where credit is due. The big man recognizes that errant outdoor light impinges on the night sky. His navigational difficulties are compounded by the unnatural sky glow washing out the stars. One of the Five Principles of Responsible Outdoor Lighting is to use warmer colors that impede our vision less, which is why even Rudolph leads the reindeer team with a red light. Kids, if you want to help Santa, dim the outdoor lights.
Along with his list of children's names and home addresses, perhaps Santa carries this or a similar star chart to find his way among all those stars. The original Platisphere (video) is set for January 1 at midnight, from which you can then find the circumpolar stars for any date or time of the year. If you head for Times Square, look for this default arrangement of the stars as the ball drops, with the Big Dipper standing on its handle at midnight. Oof, there's that light pollution issue again!
While the north circumpolar stars are always overhead, the vista to the south is slowly ever-changing. In early winter, Orion the Hunter rising in the east is most recognizable with his prominent three belt stars. Follow those three down and left to the brightest star in the night sky, Sirius, in the constellation of Canis Major, the great dog; follow those three up and right to the red giant star Aldebaran, the eye of Taurus the Bull.
The stars are seasonal calendars in the sky, their visibility determined by earth's annual revolution around the sun. As the leap year 2024 ends and the new year begins on January 1, spread the greeting, "Happy New Orbit-Around-the Sun!"
Nova
A "new" star is about to appear in the constellation Corona Borealis (CBr). A recurring nova is something few people have ever seen, and we likely will never see again, as there are only two known examples in the universe (thus far). It's basically a faint binary star that periodically explodes so violently that the outburst is briefly visible, about as bright as Santa's favorite star Polaris.
Start looking at CBr now to get familiar with the pattern so you'll recognize the nova when it happens. It's a lovely constellation that is easier to find after you take a 3-second photo with your cell phone. You may have only a few days of observing. Who knows. Again, the dynamic firmament overhead awaits your witness. Be patient; it will happen.
Solargraphs from Solstice to Solstice
While it may be cold, near the December solstice is a good time to recover and to deploy solargraphs, which are pinhole cameras that track the path of the sun over many months. By starting now you get to see the full range of the sun as it transits the sky until it peaks six months later at the June solstice.
Seasons Greetings
This holiday season, away from the revelry and outside under the realm of stars, look up and recount the silent night that began Christmas. Walt Whitman's poem When I Heard The Learn'd Astronomer expresses the sentiment well:
When I heard the learn’d astronomer,
When the proofs, the figures, were ranged in columns before me,
When I was shown the charts and diagrams, to add, divide, and measure them,
When I sitting heard the astronomer where he lectured with much applause in the lecture-room,
How soon unaccountable I became tired and sick,
Till rising and gliding out I wander’d off by myself,
In the mystical moist night-air, and from time to time,
Look’d up in perfect silence at the stars.
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