I apologize for sending this post a second time. I forgot one step: putting in the “Read more of this post” interruption. That meant that the whole thing was in the email, and you couldn’t read it like a web page, or enlarge the pictures in the way I suggested at the end.
Here is the sky scene this evening – with a startling addition.
We see the stars and planets we’ve been seeing for a while – Saturn is getting lower toward the sunset. But what are these gigantic globes that seem to be chasing us along the ecliptic, the nearest of them appearing larger than many Full Moons?
They are past Earths. That is, they are our Earth where it was, 10, 20, 30, 40, and so on days back into the past.
They serve to show how Earth hurtles around its orbit. The ecliptic is just a line on a chart; we can mentally paint it on the celestial sphere, but it doesn’t curve in toward us. So we forget to see it as the series of points where the Earth was at various dates. The globes serve to make the orbit more vivid, as if it were a circular rail around the Sun, along which Earth is sliding like a bead along a string.
Actually the past Earths are exaggerated 300 times in size, otherwise they would be too small to show. The Earth even as little as 10 days back was about 16 million miles away – 68 times farther from us than the Moon. It would appear only 10 seconds of arc wide in a telescope.
The nearest past-Earth has a D-shaped sunlit face because it is almost at 90 degrees from the Sun, just as the Moon appears D-shaped at First Quarter. That Earth is behind us; the Moon at First Quarter is crossing our orbit behind us.
You can see that this nearest Earth is just short of the point marked “antapex of Earth’s way,” which is the direction straight backward from where we are now.
The past-Earths would look more like Earths if I had drawn the equator on them, showing their tilt, but I haven’t yet figured out how to program this.
The nearest past-Earth may not look as if the trail it is on is curving in strongly enough to hit us. The trail would come in to hit the equator, at the present Earth’s rearmost point. If we were to draw an Earth on the same scale only 5 days ago, it would fill most of the sky; only one day ago, and we would be deep inside it.
There is a past-Earth colored brownish-orange; why? It is 60 days ago; it’s the one that is nearest to where Earth was at the September 23 equinox.
And there is another, down near the horizon, colored yellow. It’s the past-Earth that is nearest to where we were at the June solstice.
The series of past-Earths continues below the horizon (they are colored pink – actually, magenta). They do this to show how the girdle of Earth-positions goes completely around behind the Sun.
And here is the eastern scene tomorrow morning, when we will be looking ahead along Earth’s line of travel:
These are the future-Earths. They are at the places along the ecliptic where we will be, 10, 20, 30 and so on days ahead. The nearest of them is only just left of the “EDOT,” Earth’s present direction of travel.
The future-Earth 30 days ahead is colored blue: it is the one that’s nearest to where Earth will be at the December 21 solstice.
What caused me to think of plotting the past and future Earth’s was an idea from Daniel Cummings (creator of the Moon Hat, Soft Earth, Sun Tracker, and Star Spot, and other aides to the imagination). His idea is of a “visible Earth orbit,” and he asked me whether I had some software that could plot its appearance in the sky. At first I had trouble understanding what he meant, because he described it in terms of a sparkly dust trail, the Moon’s phases, the meridian, setting-points on the horizon – then I understood.
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DIAGRAMS in this post were made with precision but had to be inserted in another format. You may be able to enlarge them on your monitor. One way: right-click, and from the drop-down list choose “View image” Or from that list choose “Copy image”, then put it on your desktop, then open it. I would welcome learning of any other methods.
Guy, this is an amazing complement to your other diagrams depicting celestial motion! One thing is unclear to me, however: I think I understand that the yellow Earth near the horizon represents our location against the ecliptic at the June solstice, which makes sense to me because it appears to be at the southernmost point on the ecliptic in Ophiuchus. However, you state that the brownish orange Earth (between Sagittarius and Capricorns) is where we were at the September equinox. Wouldn’t we be placed at the “first point of Aries” somewhere between Pisces and Aquarius on the ecliptic on September 23 (180 deg away from the Sun)? If that is not the case, then I haven’t grasped this diagram completely (which could very well be the case LOL).
An acute question, Eric, and I need to address it when I get back to showing improved Past-Earths. No: the September equinox point on the ecliptic, off the left of the picture, is where that September Earth would appear AS VIEWED FROM THE SUN.
Think of the Earth’s path curling inward, toward the present Earth you are standing on.
OK, thank you Guy, that does make sense. I guess the June 23 solstice point happens to be back far enough in time that the points on the ecliptic showing the Earth’s location when viewed from the Sun and when viewed from Earth are close enough together that I didn’t notice the difference.
Hi Mike! Thanks for the compliment. Guy’s plot of this visualization is amazing. And his description is even better. In the article he alludes to my initial description of the visualization idea… I am posting what I wrote so you can see how he transformed my inchoate mumble into his pellucid elucidation.
“I imagine visualizing the Earth’s orbit as if it were a glowing sparkly path in the sky, stretching out from the meridian at sunset, curving around the behind the Sun and continuing down back to be at meridian at sunrise. The quarter moons would pass through this sparkly path as they cross the orbit.” – Dan via email.
Guy, This is a wonderfully new perspective of imagining our movement amongst the stars. It’s one further step to visualizing heliocentrically rather than geocentrically. Thanks to you and Dan Cummings and I hope to share this “new” way in future posts on my Facebook linking to your blog. I hope you get to refine it, too. It never ceases to amaze me how we can conceptualize new already knowing the old. This is probably the only real example of “thinking out of the box.” Well done. -Mike Kentrianakis
Fabulous, Guy! I’m glad you figured out not only what Dan Cummings was excited about, but also how to depict it. Two of you to invent this wonderful pair of perspectives on past & present earths, but only you could have invented the poetry that says it: “The ecliptic is just a line on a chart … but it doesn’t curve in toward us. So we forget to see … the series of points … the Earth was … The globes … the orbit … vivid, as … a circular rail around the Sun, along which Earth is sliding like a bead along a string.” Amazing!
The poetry is only one quarter the reason I unfailingly read you; the other three quarters are your drawings, your articulations that so precisely convey the enormous knowledge you so welcomingly invite us to easily contemplate with you, the cultured humanity of the man.
While slowly trying to make some inroads into my baffling ignorance of celestial mechanics, I keep wanting to try to sketch visual intuitions I do not know how to imagine projected sufficient thousand-word pictures to myself, like your beads along a string, but I haven’t the faintest idea what accessible tools might help me find any pictures I might be capable of (I’ve no past anywhwere in my long life that showed signs of an artist) that will catch my thoughts. Would you please share the software(s) you rely on for making your own mind visible?
Thank you.
John
I would like to know about this software, too.