The Crestone Eagle • August, 2020
Skies Over Crestone: August
by Kim Malville
August 1: The brilliant object in the morning is Venus. Its thick cloud cover hides 37 active volcanoes, which continue to spew out the carbon dioxide that has made the beastly hot planet unlivable. In the evening the moon, Jupiter and Saturn form a triangle above the southeastern horizon.
August 3: Full moon.
August 11: Last quarter moon.
August 12: The famous Perseid Meteor shower. In his song “Rocky Mountain High”, American singer-songwriter John Denver refers to his experience watching the Perseid meteor shower during a family camping trip in the mountains near Aspen, Colorado, with the chorus lyric, “I’ve seen it raining fire in the sky.”
The last quarter moon rises about midnight, so the evening before moon-rise should be the best time catching a few meteors. A spike in Perseid activity is predicted for 4 a.m. just as the sky is brightening. These meteors are small grains that escaped from Comet Swift-Tuttle when its nucleus was heated by the sun. Comet Swift–Tuttle was first reported in 322 BC by the Chinese. The comet swings between Earth and Pluto with a period of 133 years. Small rice-grain-sized particles escape from this dirty snow ball, as some of the ice that binds them sublimates. These particles travel with the same speed as the comet and follow its orbit, gradually filling up the tube of the comet’s orbit. When the earth passes through that tube of orbiting rice grains, we catch them in our atmosphere and they appear as meteors.
The Perseids are known as the “fireball champions”. Because Swift-Tuttle is larger than most comets that produce meteors, it is capable of producing larger fragments that result in unusually bright meteors or spectacular fireballs that blaze across the sky leaving tails of smoke.
Speaking of comets
Starting in July, we began to be amazed by the brightest comet in 20 years, known as NEOWISE, which made its closest approach to the Sun July 3, 2020. It is only 3 miles across but contains enough frozen water to fill 13 million Olympic-sized swimming pools. July and, hopefully, early August, it can be found near the Big Dipper in the northern skies after about 10pm. Its passage close to the sun changed its orbit such that its period has increased from about 4400 years to about 6765.8 years. Its closest approach to Earth occurred on July 23 at a distance of 64 million miles, while visible in the Big Dipper. It will get fainter as the month progresses. During the first week of August it will be in the constellation of Coma Berenices; binoculars will be needed.
In early July, Comet NEOWISE had developed three tails. The first tail is blue and made of gas of ionized atoms and molecules, which extends directly away from the sun. These ions are dragged outward from the comet by the magnetic fields of the solar wind as it streams past the comet. The second tail, perhaps a little sharper than the first, is orange-red due to fluorescent sodium. The largest tail is golden color, like that of sunlight, produced by dust particles which scatter light of the sun. It is these dust particles from comets like Swift-Tuttle that produce meteors.
In the photograph from the Gobi Desert taken on July 19, two tails are beautifully revealed. The narrow tail gives the direction of the sun. Its structure reveals different rates of gas escaping from the nucleus of the comet as well as the changing structure of the solar wind. The larger tail produced by dust particles shows the direction of motion of the comet as it drops particles behind it. Those dust particles are pushed out by the pressure of sunlight. Because of their greater mass than the ions, the particles are able to resist the pressure of the light and continue in the comet’s orbit around the sun. The unusual waves in the dust tail may be due to the rotation of its nucleus. Comets often are covered with patches of black tar-like substances which prevent gas from escaping, and we may be seeing the effects of these patches rotating in and out of sunlight.
The smallest black hole?
When very massive stars die, they collapse under their own gravity and leave behind black holes; when stars that are a bit less massive die, they explode in supernovas and leave behind dense neutron stars; stars like the sun will end up as white dwarfs. When massive black holes collide they shake the structure of space, producing gravitational waves, first observed on the earth in September 2015. Since the earth-shaking first detection of gravitations time, 50 more events have been detected in the US and Europe. In a paper published on June 23 in the Astrophysical Journal Letters, a new kind of collision has been reported. Up to this time all have involved black holes of similar mass, but this time the collision involves a black hole of 23 times the mass of the sun and a much smaller dense object with a mass only 2.6 times that of the sun. It is uncertain if the smaller object was a tiny black hole or a very large neutron star. This collision occurred 800 million years ago. That’s how long the it has taken gravity waves, traveling at the speed of light, to reach the earth on August 14, 2019. If the smaller object was a black hole, it would have been the smallest black hole yet detected, with a diameter of 9.6 miles, astonishingly, smaller than Comet Swift-Title, which produces our Perseid meteors. What a wonderful universe we inhabit! These two similar-sized objects couldn’t be more different. The comet is a collection of ice and dust with so many gaps in it that it would float in water, with a density of about 0.6 grams per cubic centimeter. The black hole is one of densest objects in the universe with the mass of 2.6 suns tightly squeezed together. Its density is 2 quadrillion grams per cubic centimeter, that’s 1 followed by 15 zeros more than water. It would not float!