Anatomy and Art

a blog by Sara Egner

The Ecliptic

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For the past year, maybe year and a half now, I’ve been making a lot of these astronomy animations for Macmillan. I really enjoy them. Most of the topics just lend themselves so well to 3D animation.  Some of them wind up being really interesting math puzzles, and you even discover very real things just playing with the settings sometimes.

In this particular animation, we wanted to show students the ecliptic, but we wanted to be able to show it to them before introducing the concept of the celestial sphere.  Most textbooks reference the celestial sphere in defining the ecliptic, so already we had this complication in how we were going to come at this.

I was also pretty challenged by the idea of how can we come from an out of orbit view into a view within orbit.  When I’m building these, I find myself setting up a lot of nulls within nulls within nulls to define different movements (orbit, rotation, angle…)  I have found that putting a camera in different levels of these nulls can be really revealing.  And in this case, I was able to go from a static camera which shared the exact position of a camera in orbit at a particular frame, so that I could switch from one camera to the next and move from that wider view into a closer view of Earth that follows it’s orbit without breaking continuity.

Fun fact: By putting the camera in a different null earlier on, I actually accidentally stumbled into a nice visualization for the analemma.  If your camera is in orbit with the Earth, and always pointed toward the sun, you can see the poles on Earth wobble toward and away from the sun, as the constant angle of the axis faces along the same XYZ coordinate in it’s orbit.  But that was a little distracting for this one.

For this one, it made more sense to go with keeping the camera on a fixed side of Earth and letting the light appear to orbit around it, even though it was actually the Earth and camera in a null orbiting the light the whole time.  This wound up being perfect for showing that transition from a heliocentric view to a geocentric one.  The illusion was already there.  And setting up a mini sun in perfect sync was easy enough.

And then, because we wanted to reference the background stars, and the zodiac constellations are literally the constellations along the ecliptic, we got to pull that in as well.  We used the spring zodiac constellations, and at first I messed this up, but when the south pole is oriented toward the sun, that’s our winter, and when the north pole is oriented toward the sun, that’s our summer, and you can see in this view that we are moving from winter to summer, so the sun would be passing through Aquarius, Pisces, and Aries.

I get better at these, the more of them that we do.  So much of astronomy just comes down to objects in motion, at vast distances, and how things look differently from different perspectives.  It’s a fun subject, and so well suited to 3D animation.

Written by Sara

July 20th, 2019 at 2:08 pm

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