Earth is about to arrive at the December solstice, the fourth of the year’s four cardinal poi
The solstice moment is Friday, December 21, 22:25 Universal Time, which is 10:25 PM in Britain, 4:25 PM in North America;s Central time zone.
Tomorrow evening, looking southwest, you are looking at the solstice.
Included again are imaginary “past Earths” – our Earth at points back along its orbit – in order to help visualize the orbit itself, as if it were a hoop around the Sun along which Earth is sliding. The nearest past-Earth is only an hour back, and is drawn at true size; the others are 10, 20, 30, and so on days ago, and are exaggerated 100 times in size.
The Earth of only an hour ago appears almost exactly on top of the moving point we call the “antapex of Earth’s way”: the direction backward, tangent to Earth’s orbit.
And, at this solstice date, the hour-ago Earth also appears almost exactly on top of another, but fixed, point in the map of the sky: the node where the ecliptic – the plane of Earth’s orbit – intersects the celestial equator.
So all these things have to be piled on this one point in our diagram! Also Mars, which happens at this time to be behind us, nearly 90° from the Sun. It’s out beyond the imaginary Earths, which would hide it, so we’ve pulled it to the front.
We’ve shown the past-Earths back along our orbit, getting smaller and smaller, as far as 60 days back – and, further back,at two more of the yearly cardinal points: the September or autumn equinox, and the June or summer solstice. You can see the September one, colored brownish for autumn leaves, in Capricornus.
And the June one is below the horizon – exactly where the Sun is. Of course. It’s the Earth six months away, at the opposite side of the orbit. It’s behind the Sun, so you can’t see that it’s colored yellow for summer sunshine.
You don’t have to stay up late to view this solstice scene. You can take a telescopic look at Mars, which is dimming and shrinking as we leaveit behind, and passed very close north of Neptune on December 7. Saturn is already down at or below the horizon, to be behind the Sun on January 2.
Be up early enough to take a look, in the twilight of the next morning, at the other side of the solstice.
A chain of future-Earths shows us our way forward along our orbit. The nearest, only an hour ahead and shown at true size, is 90° from the Sun, at the “Edot,” Earth’s direction of travel, more drily called the apex of Earth’s way. It is where the Moon is when it jumps the queue in front of us, circiing sunward at Last Quarter. And, all by geometric necessity, it is on top of the other intersection of ecliptic and celestial equator.
Down near the horizon, rising shortly before the Sun, are Jupiter and Mercury – Mercury passed about a degree north of more distant Jupiter a day ago. Half way up is Venus, half an astronomical unit (Sun-Earth distance) away and still almost at its brightest.
Venus, very visible, happens to be conveniently showing us the invisible future-Earth pf three months ahead, at the March or spring equinox.
And down there behind the Sun is the Earth of six months ahead, at the next year’s June solstice.
If you contemplate the two pictures in combination – the Friday evening scene, with the Earths following behind us, and the Saturday morning scene, with the Earths marching away ahead – you can feel you are at the midpoint, the gemstone, of a ring of Earths. Hold your arms out at shoulder level, curved with fingers touchin: you are at Head, the two equinoxes are your elbows, your fingers touch at the opposite solstic point beyond the Sun. You are sensing our planet’s orbit as almost a solid ring that you can see in the sky (Daniel Cummings‘s idea that set me thinking up these imaginary Earths).
The structure of the combined scene is one of balance. Our view, when we are at the solstice point, is symmetrical: 45° away to left and right are the autumn-equinox past-Earth and the spring-equinox future-Earth; 90° to left and right are the two nodes of ecliptic and equator, in Pisces and Virgo.
This weblog maintains its right to be about astronomy or anything under the sun.”
Today’s news is that the president of the United States, acting like a king, has declared victory over the terrorists of Isis (Islamic State in Iraq and Syria) and ordered (by, forsooth, Tweet) a complete and precipitatet withdrawal of U.S. troops from Syria.
Only minutes earlier, Isis had claimed a successful attack on a city.
The reversal of policy was taken without consultation with allies or advisers. National security adviser John Bolton and Trump supporters such as Senator Lindsey Graham were shocked and “livid” with rage. The Republican chairman of the Senate Foreign Relations Committee, Bob Corker, was due to meet Trump; the meeting was cancelled; Corker said: “It’s hard to imagine a president would wake up and make this kind of decision.”
U.S. and some allied troops had been protecting NGOs that strive to assure sanitation and clean water in cities ruined by the Syrian war; training Syrian forces (they were said to be 20 percent of the way to that target); and giving air support to the Kurdish SDF (Syrian Democratic Forces), who have done almost all the actual fighting against Isis.
Trump had recently chatted with another autocratic president, Erdogan of Turkey. Turkey wants to crush the Kurds in Syria because it associates them with Kurdish freedom fighters in Turkey. Another, Putin, benefits; Russia would prefer to be the only superpower playing with pawns in the Middle East.
Isis will now boast it has defeated and kicked out the Americans. The Kurds will be abandoned, to invasion from Turkey. And the ordinary people of Syria will be left to the mercy of Assad.
My Think Like a Mother contains a chronology of the sufferings of the Kurds.
Nice elaboration on Daniel’s circle-of-arms!
A couple of notes: Introducing the top image, you say “looking southwest, you are looking at the solstice.” Yet the hour-ago (ie proximate winter solstice) earth is near due south, per usual for the antapex at near sunset. (Though as you show here, the time the antepex is in the south shifts by an hour or two one side or the other of sunset around the two solstices; rather than at sunset, it occurs close to 6pm (standard time) this time of year, or 7pm DST around June solstice, plus or minus your local time correction for longitudinal variation from your time zone basis).
And, while I get the need for the picture to extend the ecliptic along its normal full arc beyond the crossing point, if we’re picturing the earth’s orbit itself with this exercise, then the orbital path line would loop right back to our viewing location from that hour-past point! (since we are looking back along our orbit to that point) I guess you could say that we’re looking at that hour-ago earth sitting on our own shoulder in that direction? For me at least, that makes the transposition/relation between the visible earth at our feet and that hour-ago “imagined” earth more concrete.
Yes, for the evening scene I hesitated between saying that we’re looking “west” in a kind of general sense for around-sunset views or “southwest” in another sort of general sense or “south” for where the proximate Earth actually appears, because it’s 90 degrees from the Sun.
As for where the procession of past-Earths, that is, the orbit “ring” they are riding on – would actually hit the present Earth, I get into that a bit more in the end-of-year post you’re about to see.
Guy! Thanks for the shout out – it’s a continually enlightening experience working with you. I love how you gave this nascent idea a punchy name (past and future Earths) and a thrilling and geometrically correct visualization. Dan
As the commander in chief Trump can constitutionally direct the movement of troops. He often says outlandish things but in the end he makes good decisions. Like other New Yorkers he is a loudmouth but compassionate at heart. His overriding philosophy seems to be that we should let the Middle East sort things out for themselves.
I served as a medic in the US Army. I had some great commanding officers and one who could never tear his eyes away from his own reflection in his spit-shined jump boots. In every unit I served in, the senior sergeants had much more experience and knowledge than the officers. A good commander listens to his senior staff. A bad commander lets his ego get in the way, and gets people killed.
That’s true. I hope Trump makes the right decisions based on intelligence rather than ego. I heard that even if we pull out all troops we would still use air power (from air force bases in Greece) to finish off ISIS. This would help the Kurds.
The topic of Trump and Erdogan’s chat was arms sales. Erdogan told Trump he would cancel an order for Russian fighter jets and tanks and would buy from the U.S. instead. This is beneficial for the U.S. because it brings Turkey into the U.S. orbit and away from Russia. As part of the deal, Trump apparently promised to pull out troops out of Syria.
I hope that in the finalized deal Turkey agrees to stop aggression against the Kurds. I imagine we would demand that since the Kurds are our close allies. The Kurds want their own country but Turkey, Iraq and Syria don’t want to give up any land. It’s complicated.
I ought generally to forbear from replying to comments, but to Anthony’s I have to add that a Commander in Chief who never have served in the armed forces should be especially careful to rely on his military advisers.
More has emerged about the conversation with Erdogan, who successfully demanded that Trump get American troops out of his way.
https://www.theguardian.com/us-news/2018/dec/21/james-mattis-resignation-trump-erdogan-phone-call
We can hope – hope is all that’s left – that the Turks won’t invade and smash our abandoned Kurdish allies, and that Russian influence won’t fill the vacuum left by American, reaching through Iran and Syria to the border of Israel.
The Kurds, who may be descendants of the ancient Medes, were never given their own country like so many other peoples after the fall of the Ottoman Turkish empire; have been constantly persecuted by their Turkish, Iraqi, and Iranian overlords; set up a functioning though unofficial democracy in northern Iraq after helping get rid of Saddam Hussein; and have undertaken most of the strugle to get rid of Isis, which is by no means finished.
Guy, one point of correction: Neither Clinton nor Obama served in the military (although neither claimed to understand military strategy better than his Secretary of Defense and Joint Chiefs of Staff). One could quibble about the extent to which GW Bush’s service in the Texas Air National Guard, during which he was absent without leave for six months and lost his authorization as a pilot, counts as military service. He was nonetheless honorably discharged, so I suppose that counts.
For most of my time in the Army, I was assigned to the First Armored Division in what was then West Germany, near the Czech border. Our mission was to deter a Soviet invasion. We were constantly out in the field on exercises, practicing repelling or at least slowing down our Warsaw Pact enemies. But if the Soviets invaded in full force, we didn’t stand a chance. Our deaths would be just cause for a US nuclear attack on the Soviet Union. It’s crazy, but it worked. Ivan stayed on his side of the wire, and we won the Cold War.
I don’t see any reason to believe that the Turkish army will not attack the Kurds in Syria. Erdogan just promised to bury the Kurds in their trenches; I expect he will keep his word. When US military forces are withdrawn from Syria, The Turks will have no second thoughts about attacking the Kurds.
I stand corrected about Trump’s being the only president who never experienced military service – Wikipedia also apparently needs correction:
“He became the oldest and wealthiest person ever to assume the presidency, the first without prior military or government service, and the fifth to have won the election while losing the popular vote.”
(I confess that I retrospectively corrected my post; then realized it would be better to leave it and add this comment; but was prevented from doing so till now because some technical error, which I still don’t understand, prevented me from getting back to these comments.)
The sentence in the wikipedia article is ambiguous, perhaps it could be clarified by saying, “with neither prior military nor government service.” The presidency was Eisenhower’s first elected office, but he had been a five-star general. A Venn diagram would show most presidents with both prior military service and elected office, some with only one or the other, and Trump in a cell by himself.
It’s taken me a few considerations to appreciate your past- and future-Earth diagrams (it also took you a few iterations to find the best way you could depict them), but they are growing on me. These diagrams well show the solstice as a point of symmetry in our orbit around the Sun.
Trump’s declaration of victory in Syria reminds me of GW Bush climbing out of a fighter jet on an aircraft carrier under a banner declaring “Mission Accomplished” in Iraq. Secretary of Defense James Mattis, the last of the “grown ups” in Trump’s cabinet, has resigned in obvious protest. I generally oppose US military adventures, but withdrawing our troops at this moment is a huge mistake. Trump is either an impetuous fool, or a proxy for Vladimir Putin.