Rudolph the Red Planet

Mars overload? Never.


The previous Mars posts were in reference the close pass between Earth and Mars which occurred on Monday night. However, orbital mechanics gives us something else to celebrate this holiday season. Earth, Mars, and the Sun will all align on Christmas Eve!

This particular configuration is called "opposition" as Mars will be directly opposite from the Sun with respect to Earth, or more simply Earth is directly between the Sun and Mars. For those of you who are uber keen, "conjunction" is the other time this alignment occurs, but with Mars on the far side of the Sun or the Sun directly between Earth and Mars. The diagram in Wednesday's post is actually more pertinent to this post as it illustrates the oppositions of Earth and Mars rather than their closest encounters. Jump back there for a look and then proceed on.

It's not easy to see in the diagram, but the elliptical orbits of the planets actually allow for their closest encounter and their opposition to occur separately. If all orbits were perfectly circular, the two events would be simultaneous and inseparable.

Let's step back a second, and discuss the geometry of the Solar System.

Each planet in the Solar System orbits the Sun in an elliptical orbit, as discovered by Johannes Kepler back in the day. As opposed to a circle, and ellipse has two 'centers' - termed foci - instead of one. For our Solar System, the elliptical orbits of the planets all have the Sun at one focus. But the orbit of each planet is elliptical in a different way; ellipses come in varying degrees of eccentricity, or distortion from circular. A circle is defined by an eccentricity of 0, while ellipses can have a range of eccentricities greater than 0 and less than 1. The more eccentric the orbit, the farther apart the two foci are. At an eccentricity of 1, the closed path of an ellipse breaks and becomes a parabola instead with the second focus at a distance of infinity. But that's a lesson for another day, back to Earth and Mars.

Earth's orbit is less eccentric than Mars' orbit, so the second focus of our elliptical path is closer to the Sun than the second focus for Mars. In the diagram this exaggerated to the point where Earth's orbit looks almost circular by comparison. This, combined with the oppositions plotted on the diagram, make it harder to see how the Earth can really be closer to Mars when the two aren't directly in line with the Sun, but this can be the case. Only once in much less than a blue moon will the two events occur at the same time. More often they will happen in succession as they do this year, with the closest encounter on Monday, December 18th and opposition on Monday, December 24th.

If you feel you are sinking into a geometrical quagmire, just take my work for it.

Whew, all that academic lead-up for what is hopefully still a worthwhile payoff...

The reason for this point being that in honor of this Christmas Eve spectacular, The New York Times ran an AP piece last week that proposed a cover version of "Rudolph the Red-Nosed Reindeer", with Mars as Santa's new best friend. Check out the lyrics in their entirety below and the full article here. Feel free to sing along!

Mars is a red-tinged planet
With a very shiny glow
And if you look to see it
You will find the moon in tow.

All of the other Yuletides
Santa would have at his side
The shiny nose of Rudolph
Acting as his big sleigh's guide

But this very Christmas Eve
Santa came to say:
''Rudolph, now with Mars so bright,
You can stay at home tonight.''

Then all the reindeer teased him.
And they shouted out with glee:
''Rudolph, the red-nosed reindeer
Outsourced to astronomy.''