Transmogrifier

The magnetic field lines that twist up to form solar flares occasionally become so warped that, like rubber bands under tension, they snap and break, then reconnect at other points. The gaps that form no longer hold the sun's plasma on its surface. Freed, the plasma explodes into space as a coronal mass ejection (CME).

Many solar storms aren't aimed toward us. At the high point of the solar cycle, the sun may produce as many as five CMEs in a given day; even at the low point, it averages one a day. The spherical shape of the sun means that most of them miss the Earth completely.

When the particles reach the Earth's magnetic sphere, they stretch and distort. Much like a tree in a strong wind, the day side — the first side affected — is compressed, while the night side is stretched out like a tail. When it reconnects on the night side, it releases the energy found in a bolt of lightning. While lightning lasts on the order of microseconds, however, the magnetic storm created lasts far longer. It races back toward Earth's upper atmosphere.

These particles, mainly electrons and protons, precipitate into the upper atmosphere (thermosphere/exosphere). The resulting ionization and excitation of atmospheric constituents emits light of varying color and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles.

Saturn V was loud but didn’t melt concrete

The Saturn V carried man to the moon and remains the most powerful rocket to successfully launch to orbit. It captures the imagination — but sometimes, it might capture a bit too much imagination. Abundant internet claims about the acoustic power of the rocket suggest that it melted concrete and lit grass on fire over a mile away.

Such ideas are undeniably false. In The Journal of the Acoustical Society of America, published on behalf of the Acoustical Society of America by AIP Publishing, researchers from Brigham Young University used a physics-based model to estimate the acoustic levels of the Saturn V. They obtained a value of 203 decibels, which matched the very limited data from the 1960s.

To put that number into perspective, commercial jet engines range from around 120 to 160 decibels.

“Decibels are logarithmic, so every 10 decibels is an order of magnitude increase,” said author Kent L. Gee, of BYU. “One hundred and seventy decibels would be equivalent to 10 aircraft engines. Two hundred would be 10,000 engines!”

While the Saturn V was extremely loud, that kind of power is nowhere near enough to melt concrete or start grass fires. If reports about these phenomena are true, they likely stem from radiative heating via the plume or debris.

Some of the misunderstanding comes from confusing sound power with sound pressure. The former is like the wattage from a light bulb. The latter is like the brightness from the same bulb: It depends on how far away you’re standing.

Mistakes in calculations, changes to the decibel reference system, and the propagation of misinformation have also led to compounding errors.

“The Saturn V has taken on this sort of legendary, apocryphal status,” said Gee. “We felt that, as part of the JASA special issue on Education in Acoustics, it was an opportunity to correct misinformation about this vehicle.”

NASA’s Space Launch System (SLS) Artemis 1 launch is scheduled for the fall of this year, when it will send humans back to the moon and surpass the Saturn V in terms of power and noise. The researchers have used their framework to predict SLS’s sound levels, and they plan to make acoustical measurements at its launch to help to further refine predictions.

flowering almond by Molly Dean