The Crestone Eagle • October, 2020

Skies Over Crestone: October 2020

by Kim Malville

We have two full moons this month, a meteor shower that was produced by Halley’s comet, and a magnificent Mars. We will have spectacular views of that planet as it comes closest to Earth on October 6. It will continue moving retrograde for the entire month.

October 1: Full moon, the “Harvest Moon.” Jupiter and Saturn will be high in the southern sky at the end of evening twilight.

October 2: Mars rises together with the moon around sunset. Follow these two as they move across the sky throughout the night.

October 2 & 3: Venus continues to outshine everything in the sky, except for the Sun and Moon. It almost collides with Regulus, the brightest star of Leo on these two mornings.

October 6: Mars is closest to the Earth and will be largest in the sky until 2035.  Try for a view though a telescope.

October 13: Mars is in opposition to the sun, rising at sunset, setting at sunrise, and highest in the sky at midnight.

October 14: Venus rises in the east followed by a thin crescent moon.

October 20-21: Orionid meteor shower. The tiny dust particles that create these meteors have been boiled off the nucleus of Halley’s comet. The Earth passes through the orbit of the comet twice a year, first in early May and then late October. These sand-grain sized particles pass through the atmosphere at 148,000 miles per hour.  The peak of the shower should be around midnight when 15 meteors per hour will radiate out of Orion’s raised club rising in the east.  The center of the shower lies just to the left of Betelgeuse. The shower should last until dawn.  In those morning hours you can watch Orion rise in the sky, carrying the shower with it.

October 22: The first quarter moon forms a triangle with Jupiter and Saturn in the south.

October 31: Halloween evening.  The second full moon of the month, known as a Blue Moon, rises at sunset.

Globular cluster in Scorpius, 30,000 light years from the sun. 
photo courtesy NASA, Hubble Space Telescope

 

Blue Moons

The phrase “once in a Blue Moon” has been around for more than 400 years. The earliest use of term was apparently much like saying the moon is made of green cheese—it indicated something absurd.

The meaning evolved to something akin to never or nearly ever:  “I’ll marry you when the moon turns blue” became the equivalent of “I’ll marry you when pigs fly.”

It is very difficult to fit two moons into a 30- or 31-day month. The time between successive full moons is 29.5 days.  It is no surprise that February can never have a blue moon.

Most Blue Moons look pale gray and white, indistinguishable from any other moon you’ve ever seen, unless, of course there is lots of smoke in the air.  To fit a second full moon into a calendar month is indeed rare, but it doesn’t change the physical properties of the moon itself. The color remains the same.

Black hole mergers

The great excitement among astronomers this month has been the detection of the most violent merger of black holes yet seen or heard. In the depth of space, two black holes spiraled toward each other and merged seven billion years ago, 2.5 billion years before even our solar system was formed. Gravitational waves moved across space at the speed of light, crashing on the earth’s shore to be picked us by three giant detectors: two with the U.S.-based Laser Interferometer Gravitational-wave Observatory (LIGO) and one Europe’s Virgo detector in Italy.    

These detectors have recorded hints of more than 50 mergers of black holes or neutron stars that produced gravity waves during the past 5 years. But one, detected on 21 May 2019, was different. It was not only the most distant merger, but it created the most powerful wave yet detected. I could say the greatest gravitational waves yet surfed by humans.

Papers published the past month (in Nature and the Astrophysical Journal) describe these black holes, respectively weighing 66 and 85 times greater than the sun, came together to create a black hole of 142 suns. Do the math. There are nine whole suns missing! Where did they go? That missing mass was converted into an immense gravitational wave, which many, many years later reached our rocky beach.

The center of the Orionid Shower. Orion is to the right, with the bright star Betelgeuse. photo courtesy of Sky and Telescope

A black hole with 142 solar masses instantly puts it into a class of its own. Whereas astronomers have long known of smaller black holes and of much larger ones in the centers of galaxies, those of medium size have been absent. Perhaps more interesting to astrophysicists are the origins of the two merging black holes. We don’t know of stars that are so large to collapse to such black holes. Stars that large would be too obese to hold themselves together.

These black hole must be “multigenerational.” Their parents, grandparents, their uncles and their aunts came together when they were smaller and merged many times. Most galaxies are surrounded by dense clumps of stars called globular clusters. These can contain hundreds of thousands of ancient stars and become excellent breeding grounds for large black holes.  As these heavy black holes sink toward the center of the globular cluster, they merge with other stars and get bigger and bigger. Black hole mergers must be everywhere.

Small black holes take long to merge as they may circle each other for seconds. This merger happened in a fraction of a second. These two objects, each more than 250 miles across, spun frantically before producing an immense shaking of local space-time.

What comes next? We haven’t yet detected black hole mergers in our own galaxy or our sister the Andromeda galaxy, even though together we have as many as 500 globular clusters. Any merging pairs so close to us could produce blasts of energy hitting the Earth, not so powerful that you would be knocked off your chairs, but they would be nicely audible in the LIGO and Virgo detectors. Keep reading this column and stay safe!