Astronomy

 

Book Cover-01Book Cover-01 Chapter 1 

  1. Alpha Herculis is a multiple star system in the constellation Hercules. It has the traditional name Rasalgethi or Ras Algethi (Head of the Kneeler). The traditional name “Head” comes from the fact that in antiquity Hercules was depicted upside down on the constellation maps.
  2. Ophiuchus is a large constellation located around the celestial equator adjacent to Hercules. Its name means “serpent-bearer,” and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the forty-eight constellations listed by the second-century astronomer Ptolemy, and it remains one of the eighty-eight modern constellations.
  3. The constellation Hercules is named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the forty-eight constellations listed by the second-century astronomer Ptolemy, and  it remains one of the eighty-eight modern constellations today. It is the fifth largest of the modern constellations. 

Chapter 2 

  1. In August, the constellation Hercules is upside down with respect to the horizon.
  2. Felis (Latin for cat) was a constellation created by French astronomer Jérôme Lalande in 1799. He chose the name partially because, as a cat lover, he felt sorry that there was not yet a cat among the constellations (although there are two lions and a lynx). It was located between the constellations of Antlia and Hydra. This constellation was first depicted in the Uranographia sive Astrorum Descriptio (1801) of Johann Elert Bode. It is now obsolete.
  3. The Kuiper belt, sometimes called the Edgeworth–Kuiper belt (after the astronomers Kenneth Edgeworth and Gerard Kuiper), is a region of the Solar system beyond the planets, extending from the orbit of Neptune (at thirty AU) to approximately fifty AU from the Sun. It is similar to the asteroid belt, but it is far larger—twenty times as wide and twenty to two hundred times as massive. Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar system’s formation. Although most asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed “ices”), such as methane, ammonia and water. The Kuiper belt is home to at least three dwarf planets: Pluto, Haumea, and Makemake. Some of the solar system’s moons, such as Neptune’s Triton and Saturn’s Phoebe, are also believed to have originated in the region.

Chapter 18

  1. Tharsis is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as the Tharsis Montes. The tallest volcano on the planet, Olympus Mons, is often associated with the Tharsis region but is actually located off the western edge of the plateau. The name Tharsis is the Greco-Latin transliteration of the biblical Tarshish, the land at western extremity of the known world.

Chapter 20

  1. The Local Group is the group of galaxies that includes the Milky Way, among others. It comprises more than fifty-four galaxies, counting dwarf galaxies. Its gravitational center is located somewhere between Milky Way and Andromeda Galaxy. The Local Group covers a diameter of ten megalight-years (3.1 megaparsecs) and has a binary distribution.

Chapter 27

  1. The Heel Stone lies north east of the sarsen circle, beside the end portion of Stonehenge Avenue. It is a rough stone, sixteen feet (4.9\meters) above ground, leaning inwards towards the stone circle. It has been known by many names in the past, including “Friar’s Heel” and “Sun-stone.” Today it is uniformly referred to as the Heel Stone. At summer solstice an observer standing within the stone circle, looking north-east through the entrance, would see the Sun rise above the Heel Stone.

Chapter 29

  1. The seven celestial objects visible to the naked eye are the Sun, the Moon, and the five classical naked eye planets: Mars, Mercury, Jupiter, Venus, and Saturn.

Chapter 29

  1. In astronomy, the Pleiades, or Seven Sisters (Messier 45 or M45), is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth, and is the cluster most obvious to the naked eye in the night sky. The celestial entity has several meanings in different cultures and traditions.

Chapter 31

  1. Solar output varies on shorter time scales, including the eleven-year solar cycle and longer-term modulations. Solar intensity variations, possibly as a result of the Wolf, Spörer and Maunder Minimum, are considered to have been influential in triggering the Little Ice Age, and some of the warming observed from 1900 to 1950. The cyclical nature of the sun’s energy output is not yet fully understood; it differs from the very slow change that is happening within the sun as it ages and evolves. Research indicates that solar variability has had effects including the Maunder minimum from 1645 to 1715 A.D., and part of the Little Ice Age from 1550 to 1850 A.D. that was marked by relative cooling and greater glacier extent than the centuries before and afterward. Some studies point toward solar radiation increases from cyclical sunspot activity affecting global warming, and climate may be influenced by the sum of all effects (solar variation, anthropogenic radiative forcings, etc.).
  2. Scientific consensus is that a layer of liquid water exists beneath Europa’s surface, and that heat from tidal flexing allows the subsurface ocean to remain liquid. It is predicted that the outer crust of solid ice is approximately ten to thirty kilometers (six to nineteen miles) thick, including a ductile “warm ice” layer, which could mean that the liquid ocean underneath may be about one hundred kilometers (sixty miles) deep. This leads to a volume of Europa’s oceans of 3 1018 cubic meters, slightly more than two times the volume of Earth’s oceans.
  3. “Scientists first suspected an ocean in Ganymede in the 1970s, based on models of the large moon. NASA’s Galileo mission measured Ganymede’s magnetic field in 2002, providing the first evidence supporting those suspicions. The Galileo spacecraft took brief ‘snapshot’ measurements of the magnetic field in twenty-minute intervals, but its observations were too brief to distinctly catch the cyclical rocking of the ocean’s secondary magnetic field. The new observations were done in ultraviolet light and could only be accomplished with a space telescope high above the Earth’s atmosphere, which blocks most ultraviolet light. Scientists estimate the ocean is sixty miles (one hundred kilometers) thick—ten times deeper than Earth’s oceans—and is buried under a ninety-five-mile (150-kilometer) crust of mostly ice.” - From NASA Press Release 15-033, NASA’s Hubble Observations Suggest Underground Ocean on Jupiter’s Largest Moon, March 12, 2015
  4. In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, colloquially known as the Goldilocks zone, is the region around a star within which planetary-mass objects with sufficient atmospheric pressure can support liquid water at their surfaces. The bounds of the CHZ are calculated using the known requirements of Earth’s biosphere, its position in the Solar system and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to life as it exists on Earth, the nature of the CHZ and the objects within is believed to be instrumental in determining the scope and distribution of Earth-like extraterrestrial life and intelligence.
  5. “A major question is whether planets suitable for biochemistry are common or rare in the universe. Small rocky planets with liquid water enjoy key ingredients for biology. We used the National Aeronautics and Space Administration Kepler telescope to survey 42,000 Sun-like stars for periodic dimmings that occur when a planet crosses in front of its host star. We found 603 planets, ten of which are Earth size and orbit in the habitable zone, where conditions permit surface liquid water. We measured the detectability of these planets by injecting synthetic planet-caused dimmings into Kepler brightness measurements. We find that twenty-two percent of Sun-like stars harbor Earth-size planets orbiting in their habitable zones. The nearest such planet may be within twelve light-years.”
    - From the Proceedings of the National Academy of Sciences, October 22, 2013
  6. The age of the Earth is 4.54 ± 0.05 billion years (4.54 × 109 years ± 1%). This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples. Following the scientific revolution and the development of radiometric age dating, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. The oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Comparing the mass and luminosity of the Sun to those of other stars, it appears that the solar system cannot be much older than those rocks. Calcium-aluminium-rich inclusions—the oldest known solid constituents within meteorites that are formed within the solar system—are 4.567 billion years old, giving an age for the solar system and an upper limit for the age of Earth.
  7. On August 25, 2012 Voyager 1 became the first human-made object to enter the previously unexplored region of space known as interstellar space, traveling further than anyone, or anything, in history. Voyager 2 is expected to enter interstellar space within a few years of 2016, and its plasma spectrometer should provide the first direct measurements of the density and temperature of the interstellar plasma.

Chapter 32

  1. Most of the bodies of the solar system orbit the Sun in nearly the same plane. This is likely due to the way in which the solar system formed from a protoplanetary disk. Probably the closest current representation of the disk is known as the invariable plane of the solar system. The Earth’s orbit, and hence, the ecliptic, is inclined a little more than one degree to the invariable plane, and the other major planets are also within about six degrees of it. Because of this, most solar system bodies appear very close to the ecliptic in the sky. The ecliptic is well defined by the motion of the Sun. The invariable plane is defined by the angular momentum of the entire solar system, essentially the summation of all of the revolutions and rotations of all the bodies of the system, a somewhat uncertain value which requires precise knowledge of every object in the system. For these reasons, the ecliptic is used as the reference plane of the Solar system out of convenience.
  2. Ceres is the largest object in the asteroid belt, which lies between the orbits of Mars and Jupiter. It is composed of rock and ice, is 590\miles (950\kilometers) in diameter, containing a third of the mass of the asteroid belt. It is the largest asteroid, and the only dwarf planet in the inner solar system. It was the first asteroid to be discovered on January 1, 1801 by Giuseppe Piazzi in Palermo Italy, though at first it was considered to be a planet. The unmanned Dawn spacecraft is scheduled to arrive at Ceres in early 2015.
  3. It is estimated that there are hundreds to thousands of dwarf planets in the solar system. The IAU currently recognizes five: Ceres, Pluto, Haumea, Makemake, and Eris. The exclusion of dwarf planets from the roster of planets by the IAU has been both praised and criticized; it was said to be the “right decision” by astronomer Mike Brown, who discovered Eris and other new dwarf planets, but has been rejected by Alan Stern, who had coined the term “dwarf planet” in 1990. Brown criticizes this official recognition: “A reasonable person might think that this means that there are five known objects in the solar system which fit the IAU definition of dwarf planet, but this reasonable person would be nowhere close to correct.”
  4. Pluto is the largest object in the Kuiper belt, the tenth-most-massive known body directly orbiting the Sun, and the second-most-massive known dwarf planet, after Eris. Like other Kuiper belt objects, Pluto is primarily made of rock and ice, and relatively small, about one sixth the mass of the Moon and one third its volume. It has an eccentric and highly inclined orbit that takes it from thirty to forty-nine\AU (4.4–7.4 billion\kilometers) from the Sun. Hence Pluto periodically comes closer to the Sun than Neptune, but an orbital resonance with Neptune prevents the bodies from colliding.
  5. The Coalsack Dark Nebula (or simply the Coalsack) is the most prominent dark nebula in the skies, easily visible to the naked eye as a dark patch silhouetted against the southern Milky Way. It was known prehistorically in the Southern Hemisphere and was observed by Vicente Yáñez Pinzón in 1499. The Coalsack is located at a distance of approximately six hundred light years away from Earth, in the constellation Crux.
  6. If the sun is eight inches in diameter, the average orbital distances of the planets are as follows: Mercury: 8 meters, Venus: 16 meters, Earth: 22 meters, Mars: 33 meters, Jupiter: 114 meters, Saturn: 209 meters, Uranus: 420 meters, Neptune: 657 meters. The average distance from the Earth to the Moon is 5.6 centimeters, or 2.2 inches.
  7. Only four per cent of the mass of the Universe is in the atoms that make up the stars and planets. And we’ve only ever seen half of that with our telescopes. Twenty-three percent of the mass of the Universe is invisible, “dark” matter. We know of its existence only because its gravity tugs on the visible stars and galaxies. No one knows what it is. And seventy-three per cent of the mass of the Universe is dark energy. Discovered only in 1998, this invisible stuff fills all of space and it has repulsive gravity. To say we are at sea in understanding dark energy is a bit of an understatement. Our best theory of physics is quantum theory. It has given us lasers and computers and nuclear reactors, an understanding of why the sun shines. But when quantum theory is used to predict the energy of the vacuum—of the dark energy—it gets a number which is one followed by 120 zeros times bigger than what we observe. This is the biggest discrepancy between a prediction and an observation in the history of science.
    - From the web site physics.org
  8. Centaurs are small solar system bodies with a semi-major axis between those of the outer planets. They have unstable orbits that cross or have crossed the orbits of one or more of the giant planets, and have dynamic lifetimes of a few million years. Centaurs typically behave with characteristics of both asteroids and comets. They are named after the mythological beings that were a mixture of horse and human, centaurs. It has been estimated that there are around 44,000 centaurs in the Solar system with diameters larger than one\kilometer.
  9. A sungrazing comet is a comet that passes extremely close to the Sun at perihelion—sometimes within a few thousand kilometers of the Sun’s surface. Although small sungrazers can completely evaporate during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong evaporation and tidal forces they experience often lead to their fragmentation.
  10. As of December 12, 2013 there are 1,488 known comets that come within ~twelve solar radii (~0.055 AU). This accounts for nearly one third of all comets. Most of these objects vaporize during its close approach but a comet with a nucleus radius larger than two to three kilometers is likely to survive the perihelion passage with a final radius of ~one kilometer.
  11. Aquarius is a constellation of the zodiac, situated between Capricornus and Pisces. Its name is Latin for “water-carrier” or “cup-carrier.” Aquarius is one of the oldest of the recognized constellations along the zodiac (the sun’s apparent path). It was one of the 48 constellations listed by the 2nd century AD astronomer Ptolemy, and it remains one of the eighty-eight modern constellations. It is found in a region often called the Sea due to its profusion of constellations with watery associations such as Cetus the whale, Pisces the fish, and Eridanus the river.

Chapter 33 

  1. A Moreton wave is the chromospheric signature of a large-scale solar coronal shock wave. Described as a kind of solar “tsunami,” they are generated by solar flares. They are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank who spotted them in 1959.