Monday, December 14, 2009

Elongation Charts

[Update: new and improved version here]

I saw this once in an astronomy book when I was little, but haven't encountered these anywhere since then. So I thought it was time to change that.

Click for larger image

What is shown in the chart is the elongation of every planet, that is the angle between the planet's and the Sun's position over time, projected on the ecliptic, for all of 2010. The yellow line in the middle is the position of the sun. So right after sunset the left half of the chart is above the horizon, and just before sunset the right half. In between the window of visiblity shifts out of the left and into the right side at a rate of 15° per hour. Note that the position of the ecliptic in the night sky depends on your location on the ground, but the position of the planets along the ecliptic is the same from every location.

If you know where the ecliptic is from your location, find the current date on the chart, and you know where to expect each of the planets along the ecliptic. When the planet crosses behind the Sun, it is at conjunction, when it crosses over at 180° it is at opposition. For the lower planets Mercury and Venus upper and lower conjunction are shown as the line crossing behind or in front of the Sun. Whew. Was that difficult?

The planet-tracks are color coded and marked with their symbols according to the legend, the linewidths are proportional to the planet's apparent magnitude at the given time. The vertical tickmarks denote weeks, each tick lies on a sunday. The large ticks and white circles on the right side mark full moon dates. For amateur astronomers this might serve as a "stay home"-marker ;).r

Click for larger image

If you are missing Pluto (well, I do), here is a chart with several dwarf-planets included. Be aware, however, that they are much more inclined from the ecliptic than the biggies, and therefore the projection on the ecliptic much less accurate. Also, the are, apart from ceres, much fainter and require some serious instumentation to see them. And thats my justification for not including Pluto on the planets-only chart and I'm sticking to it, even if it hurts me.

Ephemeris data from NASA's HORIZONS database
For may solar system graphics including several spacecraft: JPL Solar System Simulator

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