Skies Over Crestone: February 2020

by Kim Malville

The Heliosphere and the two Voyagers. Sky and Telescope

February 1: This is the month to fall in love with Venus, appearing brilliant and steady above the southwestern horizon. Throughout the month it will appear higher and higher in the sky, becoming ever more impressive.

February 7: Soon after sunset, look to the southwest for a great view of Venus high and bright in the sky, and Mercury beneath it.

February 9: Full moon

February 23: New moon

February 27: This evening will be a wonderful picture opportunity. The crescent moon passes Venus. Catch them some 45 minutes after sunset, and follow them as they sink toward the horizon.

Planet of the month: Venus

Venus is called Earth’s “sister planet” because of our similar sizes, mass, and proximity to the Sun. But, Venus is radically different in other respects. It has the densest atmosphere of the four inner planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet’s surface is nearly 100 times that of Earth, or roughly the pressure found 3,000 ft. underwater on Earth. Venus is by far the hottest planet in the Solar System, with a mean surface temperature of 863°F. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It may have had water oceans in the past, but these vaporized as the temperature rose due to a runaway greenhouse effect. Perhaps that will happen to Earth sometime in the future. The water has been broken apart into hydrogen and oxygen by the action of sunlight. Hydrogen has been lost forever by the planet as it is swept into interplanetary space by the solar wind. Venus’s surface is a dry desert and is periodically resurfaced by volcanism, which also releases more carbon dioxide into the atmosphere.

Constellation of the month: Perseus

Perseus is overhead as the sky darkens at the start of February. It is an extraordinary constellation for the story it reveals with five other constellations. Its brightest star is a yellow-white supergiant with the Arabic name Mirfak, which means elbow. Hinali’i is the name of the star in Native Hawaiian astronomy. The name of the star is meant to commemorate a great tsunami. According to some Hawaiian folklore, Hinali’i is the point of separation between the Earth and the sky that happened during the creation of the Milky Way.

The best-known star is Algol, dangerous and frightening because it varies in brightness.  The heavens were believed to be eternal and any change was considered ominous. What could be better than for Algol to be the awful eye of Medusa? The Double Cluster, comprising two open clusters near each other in the sky, provide one of the perfect tests for the dark sky that Mayor Danforth is championing.  Look for them to assure yourself of how lucky you are to live under such skies. 

Measurements of gas by the Voyager Spacecraft beyond the Heliosphere.
Sky and Telescope

In Greek mythology, Perseus was the son of Danaë, the unwilling object of the affection of  King Polydectes. She was protected from his advances by her son, Perseus. The King felt that he could rid himself of Perseus by sending him on a mission to behead Medusa, the Gorgon who had a head of writhing snakes, and whose visage caused all who gazed upon her to turn to stone. He believed that Perseus, like so many others, would perish in the attempt. By looking at the reflection of Medusa with her head of snakes, in his polished shield, Perseus was able to behead Medusa in her sleep. The beautiful white winged horse Pegasus sprang out of her headless body. Perseus continued to the realm of Cepheus whose daughter Andromeda was to be sacrificed to Cetus the sea monster. Perseus rescued Andromeda from the monster by pulling the bloody head out of its bag, showing it to the monster, who turned to stone and sank to the bottom of the ocean. When he returned home, he showed King Polydectes and his followers the head of Medusa, turning them too into stone. This amazing story of Perseus is captured in the neighboring constellations of Andromeda, Pegasus, Cetus, Cepheus, and Queen Cassiopeia.


The great bubble of Sol

On November 2018 Voyager 2 passed out of the great cavity produced by the solar wind, the Heliosphere. It is a great bubble blown up by the solar wind, which protects us from the dangers of outer space. Voyager 1, the faster of the two spacecraft launched 40 years ago, passed into interstellar space six years earlier. Recently the results of these two spacecraft were analyzed to reveal the extraordinary universe that lies outside our bubble.   The locations of these two spacecraft, as you can see in the illustration, lie in the bow of our moving bubble.  They find themselves in a space with hot particles, 20x to 100x more dense than those within the Heliosphere. These particles are high energy cosmic rays, which were produced in supernovae long, long ago.  We are protected from many of them by the magnetic shield produced by the solar wind. The boundary between the solar system and intergalactic space, crossed by the Voyager spacecraft, was at a distance of about 120 astronomical units (an astronomical unit is the distance between the earth and the sun, amounting to 93 million miles).

Perseus holding the head of Medusa.Urania’s Mirror published in London 1825

It is a sobering thought that this hot interstellar gas, which these space craft have entered, contains more matter than all the stars that lie within it. Stars are made of our kind of matter but account for only 7% of the mass contained in interstellar gas. Planets, elephants, and people account for even less, of course. Dark energy, which continues to be a great mystery, accounts for nearly 68% of the energy and matter in the universe. The next largest constituent is dark matter which contributes 27%.  Our ordinary matter accounts for only 5% of the total.  We are small and insignificant, minor players in the cosmic drama. On the other hand, no matter how tiny we may be, our minds seem to be able to encompass much of that vast cosmic drama.