October 22, 2017

AstroEvent: The Best Appearance of Mercury in 2011.

Mercury+Jupiter in the dusk. (Photo by Author).

If you’ve never seen the inner-most world of our solar system, this week is your chance. On Tuesday, March 22nd, the planet Mercury reaches a greatest elongation of 19 degrees east of the Sun.  Due to the varying angle of our ecliptic during different times of the year coupled with an eccentricity of 0.21 for Mercury’s orbit, not all apparitions of the innermost world are equal. [Read more...]

04.04.10-Fermi: Einstein Still Rules.


High & Low energy photons race through frothy space! (Credit: NASA/Sonoma State University/Aurore Simonnet).

High & Low energy photons race through frothy space! (Credit: NASA/Sonoma State University/Aurore Simonnet).

   We just can’t seem to get enough of NASA’s Fermi Gamma-Ray Space Telescope. The successor to the late Compton observatory that was de-orbited in 2002, Fermi has already pinpointed over 1,000 discrete gamma-ray sources, five times more than previously known. Now Fermi has also provided a rare test of Einstein’s theories of relativity. Relativity says that all electromagnetic waves (including highly energetic gamma-rays) travel through space at the same cosmic speed of 186,282 miles per second. Being a classical theory, however, what Einstein doesn’t do is meld gravity satisfactorily with the other three fundamental forces; electromagnetism and the strong and weak nuclear forces. Gravity stubbornly refuses to be unified, and such a goal has been the holy grail of physics for over the last half century. An alternative model of gravity at the microscopic scale would say that the nature of space-time is “frothy,” and a predicted effect should be a measureable drag induced on high energy photons. Recently, Fermi had a chance to put this to the test; on May 10th of last year, GRB 090510, a short gamma-ray burst 7.3 billion light years distant, was measured by Fermi’s Large Area Telescope. The verdict; gamma-ray photons varying a by a factor of a million times in energy arrived just nine-tenths of a second apart, far below what would be predicted by “frothy” space… that’s round one for Einstein!

16.03.10:Relativity Triumphant over Bizarre Binary.

The unique dance of DI Herculis. (Credit: Simon Albrect/MIT).

The unique dance of DI Herculis. (Credit: Simon Albrect/MIT).


   For years, a unique binary system has plagued Einsteinian physics. DI Herculis (DI Her) is a seemingly innocuous binary star about 2,000 light years distant. Type B stars each about five times the mass of our Sun, these stars are in a mutual orbital embrace about 0.2 A.U. apart. Visually, the system is at magnitude +8.5, and the orbit is inclined along our line of sight so that mutual eclipses occur every 10.55 days. First recorded in 1900, this feature allows the systems’ mass, luminosity and orbital characteristics to be known to a high degree of precession. For the past several decades, however, astronomer Ed Guinan at Villanova University couldn’t shake an odd effect; namely, periastron of the two stars is advancing at a rate of only ¼ what’s predicted by Einstein’s theory of general relativity. Is an unseen companion lurking in the DI Her system, or is it Albert himself who was wrong? Prediction of such anomalies as the precession of the perihelion of Mercury is one of the great cornerstones of relativity.  In a massive system such as DI Her, this effect should be even more pronounced. Like the Pioneer anomaly, several would-be theorists have pointed to this discrepancy as a potential chink in the relativistic armor…

 Enter Simon Albrecht of MIT. Using a 1.93-meter telescope to obtain a high-resolution spectrograph of the two suns, a bizarre fact has become apparent; both stars are tipped on their rotational axes, giving them an orbital “kick” at their closest approach. This configuration adequately accounts for the relativistic anomaly. Apparently, DI Her underwent a close passage of another star or massive object sometime in its history. Guinan is relieved, but will no doubt continue to receive a flood of email from alternate-gravity theorists!

22.10.09: Thank Relativity that We’re Here!

The next time you’re studying the Lorentz equation or are forced to account for Relativity on your Buzzard Ramjet trip to Sirius, thank Einstein that we’re here at all! Scientists Jacques Laskar and Mickael Gastineau at the Paris Observatory have been modeling orbital dynamics in our solar system and have come up with some “disturbing” results. It has long been known that Jupiter has a shepherding effect on the inner solar system, smoothing out planetary orbits while ejecting or sweeping up incoming debris. However, if you model the planetary orbits taking into account only classic Newtonian motion, the odds that Mercury goes out of whack in the Sun’s 10 billion year odd life span are about 60%. Throw in Einstein, and the effect shrinks to less than 1%. A careening Mercury would be a bad thing; if it impacted Venus, we would get showered with debris over a million year span, and if it hit us, well, it would just be a bad day. The best thing it could do is harmlessly impact the Sun. Even a near miss with the Earth could drastically alter our orbit, not to mention tinker with our stabilizing Moon. Fortunately, the tiny tweak that the Sun’s gravitational well gives Mercury’s eccentric orbit via General Relativity assures that a resonance keyhole with Jupiter’s orbit probably won’t happen. Keep in mind, we’re talking tiny effects that pile up over billions of years… every time an asteroid whizzes by, we launch a Space Shuttle, or LeBron performs a slam dunk, the Earth gets a tiny push. Over billions of years, tiny forces do add up (ever heard of the Butterfly Effect?) This is why astronomers cannot predict the positions of planets more than a million or so years into the future. Incidentally, the precession of Mercury’s orbit still stands as one of the great observational proofs of Relativity. One also wonders if such a perturbation might have been the fate of Theia, the Mars sized impactor that has been hypothesized to have struck a prehistoric Earth and created our Moon. So the next time you see gravity bend light at relativistic speeds, thank Einstein for protecting our home planet Earth!

See the Orionid Meteor Shower at its Peak.

Meteor season is now well underway. About midway between the August Perseids and the November Leonids is an often over-looked shower; the Orionids. The good news this year is the Orionids occur around the morning of October 21st, when the light-polluting moon is only three days past new and thus safely out of the morning sky. Expect to see up to 20-30 fast moving meteors, as was generally the reported case last year. For best results, be sure to watch several hours before dawn, or about 2-5 PM local.

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Review: Einstein for the 21st Century.

No 20th century icon is as instantly recognizable as Albert Einstein. Folks who know nothing of General, let alone Special Relativity can identify his lovable mad scientist visage, and his famous equation E=MC^2 adorns everything from t-shirts to bumper stickers. Einstein even beat out such notables as Gandhi (whom he admired) for Time magazine’s Man of the Century. Einstein for the 21st century: His legacy in Science, Art, and Modern Culture, by Peter Galison, Gerald Holton, and Silvan S. Schweber and out from Princeton Press explores the far reaching effects the man has had on modern culture and science.

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A Voyage to the Inner-Most Planet

The Solar System has just become a little more known. This year our view of Mercury, the closest planet to the Sun, has changed as the Messenger spacecraft completes its first flyby of the little known world. Late in the afternoon last week, I braved the January cold to peer west. There, in the dusk twilight, was a single shining point below the crescent Moon.

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