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THE DAILY ASTRONOMER
Tuesday, January 3, 2017
Week 18 Night Sky Calendar
Although the memory is vague, we think we promised to return on January 2nd, even though we intended to return on January 3rd, as the University Elder Circle quite kindly designated Monday as a holiday. While we always want to fulfill our promises, we also wanted to accept Jan 2nd as a holiday. Thus, we comprised: we will post this article on a Monday, but will post it as Tuesday's DA. So, if you read the title date, no need for alarm. It is still Monday, January 3rd. If, of course, you're reading this article in Australia or New Zealand or in most of East Asia, please ignore that last sentence.
Oh, and, Happy New Year!
We're delighted to see you again.
We begin the top of the year at the top of the Winter Hexagon! For those who've just arrived, we focus on a different constellation each week at or near the beginning of the night sky calendars. For the next month and a half, we will select a different "Winter Hexagon" constellation each week. Today, we find at its apex Auriga the Charioteer.
Auriga the Charioteer. Its brightest star, Capella, marks the northernmost point of the "Winter Hexagon." Just think of Capella as being the Hexagon's "Cap."
HELIOS HYPERION was arguably the most important god of all those who presided over Earth. His all important function was to drive the Sun chariot across the sky each day. The Sun, for those who've forgotten, is the benevolent sphere imparting warmth and light onto the world. As Aurora, goddess of the dawn, cast feeble light into the east, Helios Hyperion secured himself in the chariot and pulled hard on the reins, so as to control the ferocious steads that drew it forth. Every day he ascended to the greatest heights in the morning and descended toward the west in the afternoon. Each night he rested and the Sun cleansed itself in the unseen waters beneath the land.
Helios' usual routine was rather abruptly disrupted one early day before sunrise when a young man appeared in his crystalline palace. This interloper was Phaeton, a child of the Oceanid Clymene. He had been told throughout his childhood that Helios Hyperion was his father. Now grown to young manhood, Phaeton had resolved to see his father and ask about his paternity. Apart from being angry, Helios was gladdened at his son's appearance, for he had watched Phaeton throughout his childhood slowly mature from infancy to adolescence and finally to adulthood. It had been a grief to Hyperion that he could not speak with or even visit his own son. All the same, he was consoled by the knowledge that his son was safe and loved. He also knew that he, being the Sun god capable of witnessing all that transpired on Earth, would always be able to see him.
"You are, indeed, my son," Helios Hyperion quickly replied after Phaeton asked the question. "I welcome you to my home which you may now call your home, as well, should you wish to do so."
Phaeton looked at his father quizzically and said, "How am I to know you are truly my father?"
"Ask me for one wish and I shall grant it. Whatever it is you desire, I swear by the River Styz that I shall give it to you."
After a very brief pause, Phaeton answered, "I wish to drive your chariot across the sky for just one day. Grant me this wish and I shall know I am your son."
Helios Hyperion immediately regretted his offer for he knew that only he could drive the Sun chariot across the sky, The journey between the horizon was fraught with peril. The path was the home of a giant scorpion, a fearsome centaur and a menagerie of other formidable beasts. Helios was able to pass through the sky unmolested by these creatures only because his own steeds were equally fierce. Even though Helios was preternaturally strong, he still struggled throughout the day to maintain his mastery over his horses. He explained his misgivings to his son in an attempt to dissuade him from driving the chariot.
"Even Zeus, himself, is equal to the task. Only I can control these beasts. Please, my son, I implore you to choose another gift. Ask of me anything else: I can bestow upon you immortality, great powers, and an abundance of riches and would do so happily. I just ask you to withdraw your request. "
"Even Zeus, himself, is equal to the task. Only I can control these beasts. Please, my son, I implore you to choose another gift. Ask of me anything else: I can bestow upon you immortality, great powers, and an abundance of riches and would do so happily. I just ask you to withdraw your request. "
Alas, Phaeton did not.
Ultimately, Helios had to relent, for he had sworn by the River Styx and, in so doing, made a vow he could not break. Sadly, he guided the excited Phaeton to the enormous chariot. He anointed his son's eyes with nectar so he would not be blinded by the Sun's brilliance. "Pull on these with all your strength and do not relax your grip, not even for a moment."
Phaeton watched as Aurora's light intensified and the dull, pre-dawn gray brightened into bronze. "Steady on, my son," Helios advised as he watched the chariot pull forth and rapidly rise along the sharp arcs of the eastern sky. Phaeton was at once horrified by the heights they were ascending. He could indeed behold the world below him, as well as the cloud forms churning far below. In a panic, he loosened the reins. The steeds realized that they were no longer constrained and bolted straight up in a fury. Phaeton was tossed back against the chariot and entirely lost his grip on the reins. The horses abruptly descended, causing the panicked Phaeton to careen into the chariot's front section. The Sun drew too close to the land. The trees and crops burst into flame, creating the deserts. The horses reared up again and with the Sun in tow, scorched the sky, creating the Milky Way.
This commotion came to Zeus' attention. He saw the flaming Earth, burnt sky and renegade steeds of Helios' chariot. He also saw Phaeton cowering in the chariot. Zeus quickly struck him dead with a thunderbolt and was able to hold the chariot fast until Helios could take control. Despite his profound grief and misery, Helios Hyperion brought the steeds under control and continued to guide them toward the west, while the limp body of his dead son fell far below him. Poor Phaeton finally landed in the river Eridanus, where his sisters found his body. It is said that their own grief was so deep they wept tears of amber that still fall by the river bank.
High in the northern sky looms the chariot of Helios Hyperion, which is now mired in the light of the Milky Way that it created a long time ago.
MONDAY, JANUARY 2: VENUS 1.9 DEGREES SOUTH OF THE MOON (SILVER EVENT!!)
Venus is almost at its maximum brightness for the year. At magnitude -4.4, the second planet will be 16 times brighter than Sirius. Tonight, we will behold the brilliant planet close to the crescent moon in the western evening sky. A 1000-calorie confection for the eye.
TUESDAY, JANUARY 3: MARS 0.2 DEGREES SOUTH OF THE MOON
Mars is 130 times dimmer than Venus and is not as readily visible. While one can find Venus without even trying, Mars is more difficult to observe. A sky watcher will have an easier time locating Mars tonight, as the moon will appear just "above" it.
TUESDAY, JANUARY 3: QUADRANTID METEOR SHOWER PEAKS
Meteor showers are named for the constellation or star from which the meteors appear to originate. The year's first meteor shower is named for an "extinct" constellation, defined as one that is no longer officially recognized. That constellation was called "Quadrans Muralis." Invented by French astronomer Jerome LaLande (1732-1807), Quadrans Muralis represented a mural quadrant, a large device used to measure a star's position. Lalande first included Quadrans Muralis in his 1795 edition of the Fortin's Celestial Atlas. The pattern soon lapsed into obscurity as only faint stars comprised it. Those stars are now shared by the constellation Bootes and Ursa Major. This shower can produce 30 - 60 meteors an hour. This year is somewhat favorable for the meteor shower as the moon is in the crescent phase and won't produce significant lunar light interference.
WEDNESDAY, JANUARY 4: EARTH AT PERIHELION
At 9:19 a.m. today, Earth will reach perihelion. (If you're reading this passage after 9:19 a.m. today, please pardon the verb tense.) Perihelion is the point of least separation between the Sun and Earth. Our planet is at is closest approach to it parent star. Earth travels along an elliptical, not circular, orbit. A circle is a closed curve consisting of points equi-distant from a common center. An ellipse is "oval-shaped." Although, Earth's orbital path is only slightly elongated:
At 9:19 a.m. today, Earth will reach perihelion. (If you're reading this passage after 9:19 a.m. today, please pardon the verb tense.) Perihelion is the point of least separation between the Sun and Earth. Our planet is at is closest approach to it parent star. Earth travels along an elliptical, not circular, orbit. A circle is a closed curve consisting of points equi-distant from a common center. An ellipse is "oval-shaped." Although, Earth's orbital path is only slightly elongated:
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A diagram of Earth's orbit. Earth;s orbit is elliptical, not circular. The planet's distance from the Sun varies throughout the year. Earth reaches its minimum distance perihelion, on January 4th, when its distance from the Sun will be 91,404,322 miles from the Sun. On July 3, Earth will reach aphelion and will then be 94,505, 901 miles from the Sun. Though this 3.1 million mile difference seems significant, it represents about a 3% distance change throughout the year. Image: Wikipedia.com
We are now closer to the Sun than we will be for the rest of the year.
Consequently, the Sun appears slightly larger, the radiation we receive from the Sun is at a maximum, and our planet's orbital velocity is greater now than at any other time. Wonderfully, it is difficult to notice any of these changes. First of all, the Sun appears less than 3% larger now than it does in early July, when Earth reaches aphelion. We would need telescopes and precise measurement tools to notice this variation. Secondly, the variation in radiation is also slight. The top of Earth's atmosphere receives about 1.41 kiloWatts of solar energy per square meter in January, and 1.32 kiloWatts of energy per square meter in July, the maximum and minimum amounts, respectively: about a 7% difference, not enough to directly affect our weather. Thirdly, the orbital velocity varies because, as Kepler's Second Law tells us, a planet's velocity increases as its distance from the Sun decreases. Right now, Earth is moving around the Sun at about 67,750 miles per hour. In July, its orbital speed slows down to a slightly more lethargic 65,515 miles per hour. Still, our planet is still a rapid mover.
THURSDAY, JANUARY 5: FIRST QUARTER MOON
SATURDAY, JANUARY 7: PLUTO IN SOLAR CONJUNCTION
We cannot see the planet Pluto tonight. Granted, without a powerful telescope, Pluto isn't visible, anyway. Even with the aid of such a telescope, Pluto won't be observable as it will be passing on the far side of the Sun relative to Earth The technical term for this configuration is "superior solar conjunction." Pluto will emerge into the eastern pre-dawn sky later this winter, not that we'll notice.
PLANET WATCH
MERCURY: A beautiful morning planet this month, Mercury rises earlier each morning until late January. The little planet reaches its greatest western elongation on the 19th, when it will be 24 degrees west of the Sun. VERDICT: Mercury is never an easy planet to observe, but it is slightly easier this month if you venture out before sunrise and look to the east.
MERCURY: A beautiful morning planet this month, Mercury rises earlier each morning until late January. The little planet reaches its greatest western elongation on the 19th, when it will be 24 degrees west of the Sun. VERDICT: Mercury is never an easy planet to observe, but it is slightly easier this month if you venture out before sunrise and look to the east.
VENUS: (PICK PLANET!) Yes, we knew that you knew that we'd choose Venus as the pick planet again. How could we not? Our sister planet is not only at its greatest brilliance, but will reach its greatest eastern elongation on January 12th. VERDICT: Unless you hate astronomy, you will want to see Venus this month. And, if you do hate astronomy, um, well, we hope you enjoy the DA, anyway.
MARS: Venus' evening sky companion, Mars is more than a hundred times dimmer, but still brighter than all but fifteen night sky stars. If one can find Venus, one need only look a bit to the west to find Mars. VERDICT: It doesn't dazzle, but Mars is still moderately bright and therefore not to difficult to observe.
JUPITER: A morning sky object this month. The giant planet rises well after midnight, but will be high in the pre-dawn eastern sky. Jupiter is that bright "star" one sees in the morning just before sunrise. VERDICT: A beautiful planet that one can even see as the morning twilight brightens.
SATURN: Yet another morning planet. However, Saturn remains low in the eastern pre-dawn sky throughout the month. It rises about four minutes earlier each day. As winter progresses, Saturn will move into greater morning sky prominence. We can look forward to seeing Saturn in the evening sky when the spring and summer warmth returns. VERDICT: You can find it if you absolutely have to. However, Saturn will be on stage almost all year and will be easier to find as we move into spring.