SJAA Ephemeris March 2010 | SJAA Home | Contents | Previous | Next

The Shallow Sky

The pull of the planets

Akkana Peck


Mars, just over a month past opposition, rules the March nighttime sky, and there’s plenty to look at.

On the first weekend in March, Mars presents Olympus Mons face on, with Maria Sirenium and Cimmerium showing in the south, Erebus and Arcadia challenging smudges in the north.

Last month’s suspense over NASA’s Spirit rover is now resolved: sadly, the rover drivers were unable to free the little rover’s stuck wheels, and Spirit will remain where it is, near the northeast edge of Cimmerium, as a stationary research platform.

It’s been put into hibernation mode, where it is expected to survive the winter. NASA already has some ideas for cutting-edge research Spirit can do in the spring. One project involves studying the Martian core: by tracking the position of Spirit very precisely, NASA can measure tiny wobbles in Mars’s movement which may reveal whether the planet’s core is liquid or solid.

By the 13th, Solis Lacus and the “eye of Mars” is front and center, with Margaritifer starting to show to the east, and Mare Acidalium visible on the southwest edge.

On the 20th, Mars’ southern hemisphere at 9 p.m. will offer a great view of Margaritifer with all its complex bays, as well as Sinus Meridiani and Sinus Sabaeus. Meanwhile, Mare Acidalium dominates most of the northern hemisphere, with Nilokeras hanging off to the east near the terminator. By now the planet should be starting to look noticeably gibbous.

Finally, on the last weekend of the month, Syrtis Major dominates the southwest as Margaritifer and Sabaeus disappear behind the terminator.

Southward of Syrtis Major is bright Hellas, looking deceptively like a south polar cap – but the real south polar cap is tilted away from us and, since it’s autumn in Mars’ southern hemisphere, probably not big enough to be visible.

The northern hemisphere features are more subtle: look for Utopia as a dark area around the polar cap, and Nilosyrtis and Protonilus as small subtle dark features in the northern temperate zones.

A bit of Acidalium should still be visible on the terminator in the northeast.

Meanwhile, Saturn rises after 9pm and is visible the rest of the evening.

The rings are tilted nearly 4 degrees at the beginning of the month, but close to 2.8 degrees by month’s end. Always a good target!

All the other planets are too near the sun for good observing. Mercury and Venus move into the morning sky – barely – by the end of the month, while Jupiter, Uranus and Neptune stay hidden in the sun’s glare.

Pluto is still there in the early evening, but it’s low enough that it’ll be very tough to catch such a dim target.

Hey, that’s a lot of planets over in the direction of the sun, Mercury, Venus, Jupiter, Uranus, Neptune, all pulling together, with Mars almost directly opposite them. Quite a syzygy!

That’s a great word, isn’t it? “Syzygy” comes from the Latin syzygia, “conjunction,” from the Greek suzugoV (syzygos). It means basically the same thing as “conjunction” though it’s less specific: it’s basically any time when multiple planets are lined up.

Sometimes people get all excited about planetary alignments or syzygies.

Astrologers attach great significance to some of them. But nobody seems to be excited about this year’s, so we have it all to ourselves.

Whenever somebody comes to me asking about the influence on us of a planetary alignment, I start wondering how tiny the extra gravitational forces must be.

So just for fun, I calculated some rough numbers.

For this month’s lined-up planets, I tabulated elongation (the angle between the Sun and the planet, as viewed from Earth), distance from us, and mass.

Then I calculated Earth’s approximate gravitational acceleration in the direction of the sun due to each planet, using the equation: G*m/r^2 * cos(E) where m is the mass of the planet, r is its distance from Earth and E is its elongation.

Acceleration is in m/s^2 * 10,000,000.

planet distance(AU) elongation mass (kg) acceleration

Mercury 1.37 -9.9 3.30e23 0.00516

Venus 1.66 12.2 4.87e24 0.05148

Jupiter 5.98 -2.3 1.90e27 1.58221

Uranus 21.06 13.3 8.68e25 0.00568

Neptune 30.98 -15.7 1.02e26 0.00305

Total: 1.64758

Okay, .000000164758 meters per second squared? What does that mean?

Sounds small, but it’s hard to visualize. So, for comparison, I calculated the acceleration from the sun:

Sun 1.0 0 1.99e30 59308.333810

In other words, the gravitational pull of all those planets lined up in a syzygy is roughly 1/36,000 the pull the sun has on us all the time.

Tell that to your friends the next time they get all excited about the cosmic influence of a planetary alignment.


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