The oldest astronomical observatory in Asia

Cheomseongdae is an astronomical observatory in Gyeongju, South Korea. It is the oldest surviving astronomical observatory in Asia. It was constructed in the 7th century in the kingdom of Silla. Cheomseongdae was designated as South Korea's 31st national treasure in 1962. Modeled on Baekje's Jeomseongdae, which now exists only in historical records, Cheomseongdae influenced the construction of a Japanese observatory in 675, and Duke Zhou's observatory in China in 723.

Io: the most volcanic body in the solar system

Io, the most volcanic body in the solar system is seen in the highest resolution obtained to date by NASA's Galileo spacecraft. The smallest features that can be discerned are 2.5 kilometers in size. There are rugged mountains several kilometers high, layered materials forming plateaus, and many irregular depressions called volcanic calderas. Several of the dark, flow-like features correspond to hot spots, and may be active lava flows. There are no landforms resembling impact craters, as the volcanism covers the surface with new deposits much more rapidly than the flux of comets and asteroids can create large impact craters. The picture is centered on the side of Io that always faces away from Jupiter; north is to the top.

Color images acquired on September 7, 1996 have been merged with higher resolution images acquired on November 6, 1996 by the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft. The color is composed of data taken, at a range of 487,000 kilometers, in the near-infrared, green, and violet filters and has been enhanced to emphasize the extraordinary variations in color and brightness that characterize Io's face. The high resolution images were obtained at ranges which varied from 245,719 kilometers to 403,100 kilometers.

Launched in October 1989, Galileo entered orbit around Jupiter on December 7, 1995. The spacecraft's mission is to conduct detailed studies of the giant planet, its largest moons and the Jovian magnetic environment. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.
 

Airglow of the Earth's atmosphere

Airglow over the VLT (Very Large Telescope) platform.

Airglow, a faint emission of light by a planetary atmosphere, is caused by various processes in the upper atmosphere, such as the recombination of atoms which were photoionized by the sun during the day, luminescence caused by cosmic rays striking the upper atmosphere, and chemiluminescence caused mainly by oxygen and nitrogen reacting with hydroxyl ions at heights of a few hundred kilometres. It is not noticeable during the daytime because of the scattered light from the sun. The airglow at night may be bright enough to be noticed by an observer and is generally bluish in colour.
 

Oumuamua: the first interstellar asteroid

Oumuamua is the first interstellar object to pass through the Solar System. It was discovered on a highly eccentric hyperbolic trajectory on 19 October 2017, 40 days after turning around the Sun. The first observations were made by the Pan-STARRS telescope when the object was 0.2 AU from Earth, heading away from the Sun. It is the first of a new class of interstellar objects. As a result of its strongly hyperbolic trajectory, it will pass Neptune's orbit in 2022 and leave the Oort cloud in roughly 20,000 years. The amount of time the object has been drifting among the stars in the galactic disc is unknown.

Curiosity rover in search of microbial life on Mars

This image features NASA's Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life. Curiosity landed near the Martian equator on Aug. 5 PDT. In this picture, the rover examines a rock on Mars with a set of tools at the end of the rover's arm, which extends about 7 feet (2 meters). Two instruments on the arm can study rocks up close. A drill can collect sample material from inside of rocks and a scoop can pick up samples of soil. The arm can sieve the samples and deliver fine powder to instruments inside the rover for thorough analysis. The mast, or rover's "head," rises to about 6.9 feet above ground level, about as tall as a basketball player. This mast supports two remote-sensing science instruments: the Mast Camera, or "eyes," for stereo color viewing of surrounding terrain and material collected by the arm; and, the Chemistry and Camera instrument, which uses a laser to vaporize a speck of material on rocks up to about 23 feet away and determines what elements the rocks are made of.

Geyser Eruptions on Mars

Every spring on the south polar ice cap of Mars brings violent eruptions of carbon dioxide gas carrying dark sand and dust high aloft.

The seasonal frosting and defrosting of ice results in the appearance of a number of features, such dark dune spots with spider-like rilles or channels below the ice, where spider-like radial channels are carved between the ground and ice, giving it an appearance of spider webs, then, pressure accumulating in their interior ejects gas and dark basaltic sand or mud, which is deposited on the ice surface and thus, forming dark dune spots. This process is rapid, observed happening in the space of a few days, weeks or months.

The geological features called dark dune spots and spiders were separately discovered on images acquired by the MOC camera on board the Mars Global Surveyor during 1998-1999. At first it was generally thought they were unrelated features because of their appearance. The first "Jet" or "Geyser" models start to be proposed and refined from 2000 onwards. The name 'spiders' was coined by Malin Space Science Systems personnel, the developers of the camera. The unusual shape and appearance of these 'spider webs' and spots caused a lot of speculation about their origin. The first years' surveillance showed that during the following Martian years, 70% of the spots appear at the exact same place, and a preliminary statistical study indicated that dark dune spots and spiders are related phenomena as functions of the cycle of CO2 ice condensation and sublimation. Thermal imaging during 2006 revealed that the temperature of these structures are as cold as the ice that covers the area. Soon after their first detection, they were discovered to be negative topographical features: radial troughs or channels of what today are thought to be geyser-like vent systems.

The geysers' two most prominent features (dark dune spots and spider channels) appear at the beginning of the Martian spring on dune fields covered with carbon dioxide (CO2 or 'dry ice'), mainly at the ridges and slopes of the dunes; by the beginning of winter, they disappear. Dark spots' shape is generally round, on the slopes it is usually elongated, sometimes with streams (water?) that accumulate in pools at the bottom of the dunes. Dark dune spots are typically 15 to 46 meters wide and spaced several hundred feet apart. Spider features form a round lobed structure reminiscent of a spider web radiating outward in lobes from a central point. Its radial patterns represent shallow channels or ducts in the ice formed by the flow of the sublimation gas toward the vents. The entire spider channel network is typically 160–300 m across.


Dark dune spots, high resolution color image
by the HiRISE camera (Credit: NASA)

Time-lapsed imagery performed by NASA confirms the apparent ejection of dark material following the radial growth of spider channels in the ice. Small dark spots generally indicate the position of spider features not yet visible; it also shows that spots expand significantly, including dark fans emanating from some of the spots, which increase in prominence and develop clear directionality indicative of wind action.

A number of geophysical models have been investigated to explain the various colors and shapes' development of these geysers on the southern polar ice cap of Mars.

Some teams propose dry venting of carbon dioxide gas and sand, occurring between the ice and the underlying bedrock. It is known that a CO2 ice slab is virtually transparent to solar radiation where 72% of solar energy incident at 60 degrees off vertical will reach the bottom of a 1 m thick layer. In addition, the ice thickness is measured in several target areas, and it was discovered that the greatest thickness of the CO2 frost layer in the geysers' area is about 0.76–0.78 m, supporting the geophysical model of dry venting powered by sunlight. As the southern spring CO2 ice receives enough Sun energy, it starts sublimation of the CO2 ice from the bottom. This vapor accumulates under the slab rapidly increasing pressure and erupting. High-pressure gas flows through at speeds of 161 km/h or more; under the slab, the gas erodes ground as it rushes toward the vents, snatching up loose particles of sand and carving the spidery network of grooves. The dark material falls back to the surface and may be taken up slope by wind, creating dark wind streak patterns on the ice cap.

Another model explores the possibility of active water-driven erosive structures, where soil and water derived from the shallow sub-surface layer is expelled up by CO2 gas through fissures eroding joints to create spider-like radiating tributaries capped with mud-like material and/or ice. Data obtained by the Mars Express satellite in 2004, confirmed that the southern polar cap has an average of 3 kilometres thick slab of CO2 ice with varying contents of frozen water, depending on its latitude: the bright polar cap itself, is a mixture of 85% CO2 ice and 15% water ice. The second part comprises steep slopes known as 'scarps', made almost entirely of water ice, that fall away from the polar cap to the surrounding plains. This transition area between the scarps and the permafrost is the 'cryptic region', where clusters of geysers are located.

A team of Hungarian scientists propose that the dark dune spots and channels may be colonies of photosynthetic Martian microorganisms, which over-winter beneath the ice cap, and as the sunlight returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesise and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. Since their discovery, fiction writer Arthur C. Clarke promoted these formations as deserving of study from an astrobiological perspective.

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, the structures might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from UV solar radiation. A British team also considers the possibility that organic matter, microbes, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a geothermal energy source.


Further reading:
Geology of Mars
NASA Findings Suggest Jets Bursting From Martian Ice Cap
Mars' South Pole Ice Deep and Wide
Water at Martian south pole
Martian spots warrant a close look
Dark Dune Spots: Possible Biomarkers on Mars?

Supermassive Black Holes

A supermassive black hole is a black hole with the mass on the order of hundreds of thousands to billions of solar masses. Most galaxies are believed to contain supermassive black holes at their centers.


This artist's concept depicts a supermassive black hole and its
accretion disk at the center of a galaxy (Credit: NASA)

Supermassive black holes have properties which distinguish them from lower-mass classifications:

• The average density of a supermassive black hole can be very low, and may actually be lower than the density of air. This is because the Schwarzschild radius is directly proportional to mass, while density is inversely proportional to the volume. Since the volume of a spherical object is directly proportional to the cube of the radius, and mass merely increases linearly, the volume increases at a greater rate than mass. Thus, average density decreases for increasingly larger radii of black holes.
• The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut travelling towards the black hole center would not experience significant tidal force until very deep into the black hole.

There are several models for the formation of black holes of this size. The most obvious is by slow accretion of matter starting from a black hole of stellar size. Another model of supermassive black hole formation involves a large gas cloud collapsing into a relativistic star of perhaps a hundred thousand solar masses or larger. The star would then become unstable to radial perturbations due to electron-positron pair production in its core, and may collapse directly into a black hole without a supernova explosion, which would eject most of its mass and prevent it from leaving a supermassive black hole as a remnant. Yet another model involves a dense stellar cluster undergoing core-collapse as the negative heat capacity of the system drives the velocity dispersion in the core to relativistic speeds. Finally, primordial black holes may have been produced directly from external pressure in the first instants after the Big Bang.

Astronomers are confident that our own Milky Way galaxy has a supermassive black hole at its center, in a region called Sagittarius A* because:

• The star S2 follows an elliptical orbit with a period of 15.2 years and a pericenter of 17 light hours from the central object.
• Early estimates indicated that the central object contains 2.6 million solar masses and has a radius of less than 17 light hours. Only a black hole can contain such a vast mass in such a small volume.
• Further observations strengthened the case for a black hole, by showing that the central object's mass is about 3.7 million solar masses and its radius no more than 6.25 light-hours.

The Max Planck Institute for Extraterrestrial Physics and UCLA Galactic Center Group have provided the strongest evidence to date that Sagittarius A* is the site of a supermassive black hole, based on data from the ESO and the Keck telescope. Our galactic central black hole is calculated to have a mass of approximately 4.1 million solar masses.


Sagittarius A* (centre) and two light echoes
from a recent explosion (Credit: NASA)

It is now widely accepted that the center of nearly every galaxy contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation, strongly suggests a connection between the formation of the black hole and the galaxy itself.

The explanation for this correlation remains an unsolved problem in astrophysics. It is believed that black holes and their host galaxies coevolved between 300-800 million years after the Big Bang, passing through a quasar phase and developing correlated characteristics, but models differ on the causality of whether black holes triggered galaxy formation or vice versa, and sequential formation cannot be excluded. The unknown nature of dark matter is a crucial variable in these models.

At least one galaxy, Galaxy 0402+379, appears to have two supermassive black holes at its center, forming a binary system. Should these collide, the event would create strong gravitational waves. Binary supermassive black holes are believed to be a common consequence of galaxy mergers. As of November 2008, another binary pair, in OJ 287, contains the most massive black hole known, with a mass estimated at 18 billion solar masses.

IK Pegasi B: The Nearest Supernova Candidate

IK Pegasi is a binary star system in the constellation Pegasus. White dwarf IK Pegasi B, a massive star that is no longer generating energy through nuclear fusion, is the nearest known supernova candidate. When the primary evolves into a red giant, it will grow to a radius where the white dwarf can attract more matter from the expanded envelope. When the white dwarf approaches the limit of 1.44 solar masses, it is going to explode as a Type Ia supernova.


In IK Pegasi binary system, gas is being stripped away
from a giant star to form an accretion disc around
a compact companion (NASA image).

The primary is a main sequence star that displays minor pulsations in luminosity. It is categorized as a Delta Scuti variable star with a period of about an hour. Its companion is a massive white dwarf — a star that has evolved past the main sequence. They orbit each other every 21.7 days with a separation of about astronomical units. This is smaller than the orbit of Mercury around the Sun.

The distance to the IK Pegasi system can be measured directly by observing its parallax shifts against the distant stellar background as the Earth orbits around the Sun. This shift was measured to high precision by the Hipparcos spacecraft, and the distance was estimated as 150 light years. Hipparcos also measured the proper motion — the small angular motion of IK Pegasi across the sky because of its motion through space. The combination of the distance and proper motion of this system was used to compute the transverse velocity of IK Pegasi as 16.9 km/s.

The interior of IK Pegasi B may be composed wholly of carbon and oxygen, or alternatively, it may have a core of oxygen and neon, surrounded by a mantle enriched with carbon and oxygen. The exterior is covered by an atmosphere of almost pure hydrogen. Any helium in the envelope will have sunk beneath the hydrogen layer. The entire mass of the star is supported by electron degeneracy pressure — a quantum mechanical effect that limits the amount of matter that can be squeezed into a given volume.


A comparison between the IK Pegasi B (center), its companion
IK Pegasi A (left) and the Sun (right). (Credit: RJHall)

IK Pegasi B is considered to be a high-mass white dwarf, at an estimated 1.15 solar masses. Its radius can be estimated from known theoretical relationships between the mass and radius of white dwarfs, giving a value of about 0.60% of the Sun's radius. Thus this star packs a mass greater than the Sun into a volume roughly the size of the Earth. The massive, compact nature of a white dwarf produces a strong surface gravity — over 900,000 times the gravitational force on the Earth. The surface temperature is about 35,500K, making it a strong source of ultraviolet radiation. Under normal conditions this white dwarf would continue to cool for more than a billion years, while its radius would remain unchanged.

At some point in the future, IK Pegasi A will consume the hydrogen fuel at its core and form a red giant. The envelope of a red giant can extend up to a hundred times its previous radius. Once IK Pegasi A expands to the point where its outer envelope overflows the Roche lobe of its companion, a gaseous accretion disk will form around the white dwarf. This mass transfer between the stars will also cause their mutual orbit to shrink. Should the white dwarf's mass approach the Chandrasekhar limit of 1.44 solar masses it will no longer be supported by electron degeneracy pressure and it will undergo a collapse. If the core is made of carbon-oxygen, increasing pressure and temperature will initiate carbon fusion in the center prior to attainment of the Chandrasekhar limit. The dramatic result is a runaway nuclear fusion reaction that consumes a substantial fraction of the star within a short time. This will be sufficient to unbind the star in a cataclysmic, Type Ia supernova explosion.

A supernova would need to be within about 26 light years of the Earth to effectively destroy the Earth's ozone layer, which would severely impact the planet's biosphere. IK Pegasi system is not likely to pose a threat to life on the Earth, however. It is thought that the primary star is unlikely to evolve into a red giant in the immediate future. As shown previously, the space velocity of this star relative to the Sun is 20.4 km/s. This is equivalent to moving a distance of one light year every 14,700 years. After 5 million years, this star will be separated from the Sun by more than 500 light years. This is outside the radius where a Type Ia supernova is thought to be hazardous.


This video shows a thermonuclear flame burning its way through a white dwarf star. The flame produces hot ash, which buoyantly rises as the flame burns. The ash breaks out of but remains gravitationally bound to the surface of the star and collides at a point on the opposite side of the star from the breakout location. The blue shows the approximate surface of the star and the orange shows the interface between the star and the hot ash produced by the flame. (Credit: DOE NNSA ASC/Alliance Flash Center at the University of Chicago)

The Story of Gamma-ray Bursts

Gamma-ray bursts are flashes of gamma rays connected with extremely energetic explosions in distant galaxies. They are the most luminous electromagnetic events occurring in the universe.

This illustration shows the life of a massive star as nuclear fusion converts lighter elements into heavier ones. When fusion no longer generates enough pressure to counteract gravity, the star rapidly collapses into a black hole. Energy may be released during the collapse along the axis of rotation to form a gamma-ray burst. (Credit: Nicolle Rager Fuller/NSF)

"The death star": BBC documentary on the first stars in the universe and gamma-ray bursts.

The Key to the Cosmos

Prof. Jim Al-Khalili investigates the atom by looking at radioactivity, the Atom Bomb and the Big Bang, and even why we are here and how we were made. He shows that, in the quest to understand the atom, the mystery of how the entire universe was created became revealed.

A Very Short History of Astronomy

2,500 BC - Stonehenge, one of the most famous sites in the world today, once served as a burial ground. Archaeoastronomers claim that Stonehenge represents an ancient observatory, and that the site had astrological and spiritual significance as well.

650 BC - Babylonian Venus tablet of Ammisaduqa is the oldest significant astronomical text that we possess. This document, recorded on cuneiform tablets, lists the first and last visible risings of Venus over a period of 21 years.


Stonehenge (Andrew Dunn); ................. Solar eclipse (Luc Viatour); .......... Thales; .................. Hipparchus

585 BC - Thales of Miletus predicts a solar eclipse. A battle in progress between the Lydians and the Medes is spontaneously halted by this eclipse.

150 BC - Hipparchus, the greatest astronomer of antiquity, uses parallax to determine that the distance to the Moon. In 134 BC, he discovers the precession of the equinoxes. Hipparchus ranks stars in six magnitude classes according to their brightness: he assignes '1' to the brightest stars, and '6' to the stars which can be barely seen with the naked eye.

46 BC - Julius Caesar adopted a calendar based upon the 365 1/4 day year length originally proposed by Greek astronomer Callippus. 46 BC had 445 days due to the errors that had accumulated in the pre-Julian calendar.

628 - Brahmagupta, the head of the astronomical observatory at Ujjain, writes a text on astronomy, Brahmasphutasiddhanta (The Opening of the Universe).

990 - Abu-Mahmud al-Khujandi builds a huge observatory near Tehran, Iran, and observes a series of meridian transits of the Sun, which allowed him to calculate the tilt of the Earth's axis relative to the Sun.

1054 - Crab Supernova (SN 1054) is observed on Earth by Chinese, Japanese, Arab, and American Indian astronomers. It was bright enough to see in daylight for 23 days.


Crab Nebula (NASA); ........................... Nicolaus Copernicus; ............................... De Revolutionibus

1543 - Nicolaus Copernicus' epochal book, De revolutionibus orbium coelestium, is published just before he died. This is often regarded as the starting point of modern astronomy.

1577 - Danish astronomer Tycho Brahe uses parallax to prove that comets are distant objects and not atmospheric phenomena. Tycho is credited with the most accurate astronomical observations of his time.

1609 - Johannes Kepler states his first two laws of planetary motion: 1. The orbit of every planet is an ellipse with the sun at a focus; 2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time.


Tycho Brahe; ................... Johannes Kepler (Aldaron); .................... Galileo facing Inquisition

1610 - Galileo Galilei uses a small telescope to make the greatest astronomical discoveries of all time: the discovery of the four largest satellites of Jupiter, lunar mountains and craters, the phases of Venus, the Milky Way as a multitude of densely packed stars, and the observation and analysis of sunspots.

1687 - The Philosophiae Naturalis Principia Mathematica, mathematical principles of natural philosophy, a three-volume work by Isaac Newton, is published on 5 July 1687. It contains the foundation of classical mechanics, as well as the law of universal gravitation and a derivation of Kepler's laws for the motion of the planets.

1705 - Edmund Halley predicts the periodicity of Halley's comet and computes its expected path of return. In 1718, he discovers stellar proper motions by comparing his astrometric measurements with those of the Greeks.


Newton's telescope (Andrew Dunn); ........... Comet Halley (NASA); ....................... Charles Messier

1771 - Charles Messier publishes his first list of nebulae. The purpose of the catalog was to help comet hunters to distinguish between permanent and transient objects in the sky.

1781 - William Herschel discovers Uranus. He constructed more than 400 telescopes, discovered two moons of Saturn and two moons of Uranus, created extensive catalogs of nebulae and double stars, and concluded that the Milky Way is in the shape of a disk.

1814 - Joseph von Fraunhofer invents the spectroscope, and discovered 574 dark absorption lines appearing in the Sun's spectrum.

1838 - Friedrich Bessel, Friedrich Georg Wilhelm Struve, and Thomas Henderson measure stellar parallaxes, providing the first accurate measurements of interstellar distances.


Planet Uranus (NASA); ......................................... Herschel's 40 foot telescope; ................ Kirchhoff's first spectroscope

1860 - Gustav Kirchoff and Robert Bunsen discover that each element has its own distinct set of spectral lines and use this fact to explain the solar dark lines.

1908 - Henrietta Swan Leavitt discovers the Cepheid period-luminosity relation, providing an important yardstick for measuring distances in the Universe.

1910 - Ejnar Hertzsprung and Henry Russell study the relation between magnitudes and spectral types of stars. The Hertzsprung-Russell diagram represented a huge leap forward in understanding stellar evolution.

1915 - Albert Einstein completes his theory of general relativity. 'Matter tells space how to curve, space tells matter how to move'.

1922 - Alexander Friedmann finds a solution to the general relativity field equations which suggests a general expansion of space.

1923 - Edwin Powell Hubble profoundly changes our understanding of the universe by demonstrating the existence of other galaxies besides the Milky Way. Hubble also devises a system for classifying galaxies, according to their appearance in photographic images.


Andromeda Galaxy (John Lanoue); ........... Hubble's law (Brews Ohare); ............ George Gamow

1929 - Edwin Hubble and Milton Humason formulate the empirical Hubble's law -- the linear redshift-distance relation, thus showing the expansion of the universe.

1929 - George Gamow, a Russian-born physicist and cosmologist, proposes hydrogen fusion as the energy source for stars. He discovered alpha decay via quantum tunneling and worked on star formation, stellar nucleosynthesis, big bang nucleosynthesis, etc.

1930 - Clyde Tombaugh discovers the dwarf planet Pluto.

1930 - Subrahmanyan Chandrasekhar discovers the white dwarf maximum mass limit. The limit describes the maximum mass of a white dwarf star, above which a star will ultimately collapse into a neutron star or black hole.

1931 - Karl Guthe Jansky, American physicist and radio engineer, discovers radio waves emanating from the Milky Way. He is considered one of the founding figures of radio astronomy.

1931 - Roman Catholic priest Georges Lemaître proposes his 'hypothesis of the primeval atom', what became known as the Big Bang theory.

1933 - Fritz Zwicky applies the virial theorem to the Coma galaxy cluster and obtains evidence for unseen matter, what is now called dark matter. Zwicky was an original thinker, with many important contributions in astronomy.


Subrahmanyan Chandrasekhar; ... Cosmic Microwave Background (NASA); ... The Horn Antenna in Holmdel Township

1965 - Arno Penzias and Robert Wilson discover the cosmic microwave background radiation, predicted in 1948 by Ralph Alpher, George Gamow and Robert Herman.

1967 - Jocelyn Bell and Anthony Hewish discover the first radio pulsars, the greatest astronomical discovery of the twentieth century.

1971 - Cygnus X-1, a galactic X-ray source in the constellation Cygnus, is identified as a binary black hole candidate system.

1980 - Alan Guth, a theoretical physicist and cosmologist, proposes the inflationary Big Bang universe as a possible solution to the horizon and flatness problems.

1998 - Published observations of Type Ia supernovae by the High-z Supernova Search Team, followed in 1999 by the Supernova Cosmology Project, suggest that the expansion of the universe is accelerating.



Further reading:

Archaeoastronomy and Stonehenge
Astronomiae Historia
C41/ICHA website
Society for the History of Astronomy
Wikipedia History of astronomy

Exceptionally Deep View of NGC 4921

Yet another amazing video created from images taken by the NASA/ESA Hubble Space Telescope. The video reveals lots of new details of the galaxy, as well as a rich background of remote galaxies stretching back to the early Universe.

3D animation of galaxies

This video was produced by Frank Summers, currently working as an astronomer for NASA. This animation of galaxies from the Hubble Space Telescope shows galaxies distributed over 10 billion years of cosmic time.

Hypatia of Alexandria: the ancient Greek mathematician

Hypatia was the first woman who was studying and teaching advanced mathematics. During her lifetime, Alexandria had the world’s greatest library. She was a teacher and the school’s director at the Neoplatonic School of Philosophy. Hypatia was famous for her books on philosophy, mathematics, and other subjects. It is thought that Hypatia invented the astrolabe.

The comprehensive article on Hypatia at wikipedia

Impact Crater Formation

(Moon crater Dedal as photographed by the crew of Apollo 11)

Four billion years ago the Earth, the Moon, and every other Solar System object were heavily shot by impact comets and asteroids. You can see craters on rocky planets, on most moons and asteroids. Large craters usually have several rings around, intermediate have a central peak, and small craters are bowl-shaped.

The theory of impact crater formation must be very complex, searching the web I haven't found any simple (or simplified) explanation to reproduce here. In a lack of an easy theory, however you can conduct experiments, see the video below.

The Hawking Paradox: Video

The strange and exciting mix of general relativity and quantum mechanics results in the so called black hole information paradox. The Discovery Channel show "The Hawking Paradox” explains that information lost in black holes could be saved in parallel universes where no black holes exist. See the complete 49 min video here: