Mars dead ahead

It occurred to me to plot the EDOT in both ways and see how much they differ.


The EDOT is the thing I was puzzling over earlier, the Earth’s direction of travel, as Shannon Templeton called it, otherwise known as the Apex of the Sun’s Way.

In this picture the orange symbol is the first approximation, that is, the point 90 degrees west of the Sun. The white symbol is the direction calculated with somewhat greater accuracy to be tangent to the Earth’s orbit.

They at first weren’t easy to see (until I moved the labels), because this part of the diagram happened to be cluttered by the presence of Mars. Yes, Mars too is ahead. If you are out on Earth’s front, that is, around dawn, looking in Earth’s direction of travel, you will see Mars seeming to lead the way.

This would have been more exactly so on February 7, when Mars was at “west quadrature.” That is the term for the moment when a planet is, from our viewpoint, 90 degrees from the Sun. Orange Mars would then have been directly above the orange EDOT symbol.

Quadrature isn’t an entirely uninteresting geometrical happening. It’s half way between the planet’s utter lostness (conjunction behind the Sun, which for Mars was 2015 June 14) and its triumph (its opposition, 2016 May 22). It is when the planet gets about the widest shadow on its western side. It, along with the time when Mars will begin to rise before midnight (early March), and the stationary moment (April 17), are signs of the beginning of the planet’s season of prominence.

What is in general happening in the morning sky is that the planets are getting spread wider apart: Mercury and Venus sinking toward the Sun; Saturn and Mars getting left farther behind in the opposite direction.


7 thoughts on “Mars dead ahead”

  1. It is a thrill to see the EDOT included in your images; I have always wanted to see it visualized in this way.

    When I stopped thinking about the Earth’s orbit and thought about the EDOT for a highly elliptical orbit, I was also very surprised to see it could be far more or less than 90 deg away from the Sun. As always, the wonderful training my astronomy professors gave me in college helped me figure this out. I will always be grateful to Dr. Dan Caton and Dr. Joseph Pollock at App State for being such amazing mentors.

    On clear dark nights, I love to lie in the grass and try to visualize as many different motions as I can. Orientations are also very enjoyable to visualize; I start with finding the galactic plane and then looking to Polaris to see how our solar system tilts in relation to the Milky Way. Then I look to the Apex of the Sun’s Way and visualize how our tilted solar system is moving followed by finding the EDOT and imagining the Earth racing along in relation to all the other orientations I visualized earlier.

    On the very darkest nights, I can almost trick myself into “feeling” the motion which is very enjoyable indeed! It makes the night sky feel *almost* interactive. :)

    1. Hey Shannon:

      I too like watching the apparent movement of the moon and sun.

      I like viewing the moon through branches of a tree, while sitting stable in one place.. Then I can view the moon as it passes through the branches. As the moon passes up over the next branch, it starts out like a diamond above the tree limb and then grows in size above the branch.

      It’s also fun to watch the clouds pass by and try to guess where the moon will appear behind the next passing cloud.

      Another fun thing is to watch the shadow of the sun move over a landmark on the ground.

      1. These are enriching ideas. The watching of cloud-shadows moving over hillsides and fields will have occurred to most people, but the use of branches to reveal the movements of the moon will not.

        1. Thanks, Guy. You’ve been very enriching as well over the years.

          The diamond at the top of the next branch reminds me of the diamond ring analogy during a solar eclipse.

          I also should clarify my comment. I wasn’t being redundant. I meant keeping your body motionless while sitting in one place.

          To clarify the last sentence in my last comment, a landmark is whatever you decide to use to mark the land. It could be a small stone under the shadow of a branch or pole. As the shadow leaves the rock, first one edge of the rock takes on a barely perceptible brightening from the penumbra of the shadow, then it brightens fully. Then the same sequence occurs over the rest of the stone.

  2. Why is your calculated EDOT more than 90 degrees from the sun?

    Is it because a tangent is a straight line and doesn’t take into account gravitational deflection?

    If so, the orange symbol would be more accurate.

    1. I think I figured it out. We are approaching aphelion in our elliptical orbit so the EDOT would be greater than 90 degrees.

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