THE CELESTIAL CONVERGENCE: Signs in the Heavens - Planets Mercury, Venus and Saturn Align in the Morning Sky Over Egyptian Pyramids!

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December 03, 2012 - SPACE - The upcoming Mercury-Venus-Saturn alignment, while not a real conjunction, is sure getting a lot of attention thanks to an inaccurate illustration on the Internet, depicting the three over the Pyramids of Giza. The planetary trio will be approximately equidistant and span an angle of 14 degrees (equal to 1 1/2 fists extended at arm’s length against the sky) on Monday morning December 3. They’ll also appear in virtually the same lineup the mornings before and after.

A more correct view of the planets and Giza pyramids on the morning of Dec.. 3.
From bottom to top: Mercury, Venus and Saturn. Illustration created with Stellarium

When astronomers refer to a conjunction of two or more celestial bodies, they usually mean the objects are lined up closest together north-south of one another. When due south and highest in the sky, two planets in conjunction are stacked on top of each other. There are also conjunctions in longitude, when two celestial objects are closest together east-west or side-by-side.  Since none of the three planets is in conjunction, the December 3 gathering is simply an interesting alignment. You’ll also notice from the diagram that for the next few mornings their configuration changes little. The word planet comes from the Greek aster planetes or “wandering star”. And that’s exactly what they do. Ancient peoples thought they were carried around the Earth on invisible crystalline spheres.

Mercury, Venus and Saturn – along with Spica, which is similar to Saturn in
brightness – will appear together in the southeastern sky at dawn. The maps
show the scene about one hour before sunrise. Maps created with Stellarium

Today we know the truth – each is on a orbital spiral at a different distance from the sun with a period that depends on that distance. Mercury is closest and spirals fastest at 88 days; distant Neptune requires 165 years. Planets are frequently in conjunction because they all follow the same path with the sky, often referred to as the ecliptic. It follows that if you’re all driving the same highway at different speeds, sooner or later two or more planets will pull up alongside each other.

The ecliptic is the path followed by the planets, moon and sun across
the sky. This narrow “highway” is a consequence of the planets
orbiting the sun in nearly the same flat plane.

From our perspective, they’ll appear close together in the sky.  And since the planetary highway is approximately circular like a racetrack when viewed from a two-dimensional angle, interesting gatherings or conjunctions happen repeatedly over the months and years.  So if you combine the planets’ varying speeds according to distance, their shared “roadway” and our changing perspective on them as Earth orbital spiral with the sun, you’ll understand why the current morning planet alignment will soon be broken.

Now, as it relates to the illustration, there are several inaccuracies in the picture you should know about.  First, let’s take the alignment itself. While it’s true the three planets will be nearly equally spaced across a 14-degree swath of sky next Monday, they’ll appear at a much steeper angle from Cairo than the photo/illustration shows. And they won’t queue up in a perfectly straight array either — notice that the “line” sags at Venus.  There’s also a little problem with the illustration’s perspective. After consulting a map, it was easy to determine the photo shows the pyramids as you face north. From this perspective, the smallest pyramid (Menkaure) lies to the left and tallest (Khufu) on the right. Unfortunately no planets are visible from this angle, because they’re all to the photographer’s back in the opposite quarter of sky. Whoops!

Inaccurate photo/ illustration of the supposed planetary alignment
over the 3 great pyramids of Giza circulating on the Internet.

For a completely accurate portrayal of the scene during the alignment, we’d need to walk over to the other side of the pyramids and re-shoot the picture facing southeast. From that vantage point, you’d see something much closer to the scene above.  As for a lineup like this occurring every 2,737 years, well, alignments happen all the time including those involving three bright planets. While this exact configuration may be rare, the alignment itself is not. That’s not to say that the event isn’t worthwhile to watch. Hey, I’d be happy to see three planets above the Pyramids of Giza, but better and brighter alignments occur all the time, like the similarly-spaced dawn trio of Mercury, Venus and Jupiter last August.  Whether you’re standing in front of pyramids or watching from your apartment lawn, I hope you’ll be able to watch the trio as they meet, greet and go their separate ways in the coming days. - Astrobob [Edited for clarity].