DECEMBER 2017 • 37
THE STARRY DOME • BERT STEVENS
Phoenix, the Phoenix Distant stars still waiting to rise
reek mythology has many birds scattered through its stories, including the Phoenix. After living for 1,400 years, the Phoenix would die in sparks and flames. From the ashes, the Phoenix would be regenerated and live again. This bird is associated with the Sun, which goes through daily cycle of dying in the west each evening and being reborn in the east the next morning. Found low in the southern sky each December, the constellation Phoenix flies into the sky, but never completely rises above the southern horizon. It was first depicted in a celestial atlas published in 1603 by German uranographer (a celestial cartographer or mapmaker) Johann Bayer in his Uranometria. However, it was actually created by Dutch-Flemish astronomer Petrus Plancius and announced on a celestial globe released in 1597. The ecliptic does not pass near Phoenix, so the planets never enter this constellation. Phoenix is also far from the Milky Way, so there are no star clusters to be found here. However, there is another kind of cluster that can be found in Phoenix, a cluster of galaxies. In the northwestern corner of this constellation is one of its two major galaxy clusters, called the Phoenix Cluster. This is one of the largest known galaxy clusters, with the mass of two thousand trillion times the mass of our Sun. This huge cluster is 5.7 billion light-years from Earth and it was only discovered in 2010. This cluster was first detected with a radio telescope that observes in the frequency band that starts in the microwave and extends to just below the infrared. This telescope, which is almost four hundred inches in diameter, is located at the Amundsen–Scott South Pole Station in Antarctica where there is very little water vapor in the air to block the signals from space. This cluster is producing stars at a prodigious rate, some seven hundred new stars each year. Compare this to a single galaxy that produces a new star every few years. As a result, this cluster has three trillion stars. More than half of these stars are in the central galaxy of the cluster, an elliptical galaxy that was formed by absorbing surrounding smaller galaxies. Around this galaxy is a halo of stars that extended 1.1 million light-years from its center. This makes it twenty-two times the linear size of our galaxy, the Milky Way. With all the star formation
happening in this galaxy, it can only grow larger. Astronomers believe that this is a short-term (at least in astronomical terms) growth spurt, and it will end in less than a hundred million years. The Chandra X-Ray Observatory orbiting the Earth discovered that it is the strongest source of x-rays yet observed. X-rays typically come from the hot gasses where the fast-moving atoms collide frequently, releasing some of their energy as x-rays. In this galaxy, they come from the cooling gas around the core. One of the most massive black holes known to exist is at the center of this galaxy. It has a mass that is around twenty-billion times the mass of our Sun, roughly the mass of two dwarf galaxies. The black hole is seventy-three trillion miles across, nineteen times the distance from the Sun to Pluto. The black hole absorbs 60 times the mass of the Sun each year from the surrounding galaxy, so it is still growing. The black hole at the center of most galaxies stream out tremendous jets of matter that continuously heat up the gas around the core. The Phoenix Cluster’s central galaxy’s black hole has very weak jets, so the gas around it is able to cool naturally by emitting radiation like x-rays. The black hole’s gravity has drawn in a huge quantity of gas toward the core. As this massive amount of gas cools, it is able form local pockets of denser gas that collapse to form new stars. This process gives this galaxy the ability to create new stars at that astounding rate of 700 stars every year.
The Planets for December 2017 Mercury and Saturn are together in the evening sky, just seven degrees above the southwestern horizon at the beginning of the month. They will both be too close to the Sun after the first week of the month to be seen. On Dec. 1, Mercury will be magnitude +0.2 with a 35 percent sunlit disc that is 8.0 seconds-of-arc across. Saturn will be at magnitude +0.5 with a disc that is 15.0 secondsof-arc across. Its Rings are 34.1 seconds-of-arc across and they are tilted down 26.8 degrees with the northern face showing. Both will set by 7:15 p.m. Saturn will be moving slowly eastward in western Sagittarius while Mercury moves westward from western Sagittarius into south-central Ophiuchus. It then turns back eastward ending the month is southeastern part of that
Calendar of Events – DECEMBER 2017 (MST) 03 10 12 14 17 21 21 26 31
8:47 a.m. 12:51 a.m. 7 p.m. Morning 5:30 p.m. 9:28 a.m. 2 p.m. 2:20 a.m. 6 p.m.
Full Moon Last Quarter Moon Mercury between Sun and Earth Geminid Meteor Shower New Moon December Solstice-Winter begins Saturn on the far side of the Sun First Quarter Moon Aldebaran behind the Moon
The constellation of Phoenix, the Phoenix, rides along our southern evening during the evening hours in December. While this constellation’s name is from Greek mythology, it is a modern constellation created in 1597. One of the most massive galaxy clusters that has been discovered is in the northwest corner of Phoenix. The southern end of this constellation never rises above our southern horizon.
constellation. Moving from central Virgo to western Libra this month, Mars is shining at magnitude +1.6. It has a disc 4.0 seconds-of-arc across and it is ninety-four percent illuminated. The God of War rises around 4 a.m. and it can be found 36 degrees above the southeastern horizon as it gets light. The King of the Gods is now firmly in the morning sky, rising just before 5 a.m. It is moving eastward in west-central Libra, passing less than a degree from the star Zubenelgenubi on Dec. 23. Jupiter’s disc is 32.0 secondsof-arc across at midmonth. This Gas Giant shines at magnitude -1.8 and it is twenty-seven degrees above the southeastern horizon as it gets light. Venus is too near the Sun to be seen this month, but Mercury will reappear in the morning sky for the last third of the month. The Messenger of the Gods will be magnitude -0.3 as the month ends with a disc that is 6.8 seconds-ofarc across and 61 percent illuminated. It will be 11 degrees above the east-southeastern horizon, having risen around 6:30 a.m. The December Solstice occurs on Dec. 21 at 9:28 a.m., when the Earth’s northern hemisphere is at its maximum tilt away from the Sun. At that instant, the Sun will be at its southern-most point in our sky, with the Sun’s center at declination 23.436 degrees south of the Equator. This is the shortest day and longest night in the Northern Hemisphere. So take advantage of the darkness and “keep watching the sky”! An amateur astronomer for more than 45 years, Bert Stevens is co-director of Desert Moon Observatory in Las Cruces.
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Published on Dec 4, 2017