Stunning Astronomy and Astrophysics

Quiz: General Knowledge in Astromomy

This article gives a review of Flysky's lessons in astronomy and astrophysics, published on HubPages. HubPages is an open encyclopedia with more than million articles in every imaginable topic – that are called hubs. HubPages are known on the high quality of its articles, this site has become one of the 50 most visited US sites on the Internet (source: Wikipedia.org – HubPages). The specialty of this encyclopedia is that authors can comment published articles. In the category Education and Science one can find amazing hubs related to all sciences, including “Astronomy and Space Exploration".

Flysky is a scientist and an HubPages author who writes articles primarily in a fields of astronomy, physics and mathematics. Here we give an overview of Flysky's hubs related to astronomy and astrophysics. Moreover, here these hubs will be categorized into the appropriate branches of astronomy and astrophysics. A short description of these branches will be given as well.

Astronomy is one of the oldest sciences, the science that tend to describe and understand the universe. While before astronomy was a branch of mathematics, nowadays it is usually related to physics. The reason is that research method moves from mathematics to the methods typical for physics, like spectrography.

Constellations and Night Sky

Courses in astronomy usually begins with this subject. We learn how stars and other celestial objects are grouped into constellations. The night sky is divided into 88 constellations, in order to provide navigation and classification of stars. We differentiate seasonal constellations, as the consequence of the Earth's revolution. There are constellations of fall sky, winter sky, spring sky and summer sky. Every season has its typical constellations that dominate the night sky. There are also circumpolar constellations, that are always visible in the sky. These are constellations around the celestial north pole and south pole.

Observation of planets is a specially popular activity. Even observation by the naked eye is very interesting whereas small telescope shows all richness of color in case of Jupiter or Saturn. Interestingly, the farthest planet that is still visible by the naked eye is not Jupiter but Saturn.

Observation of night sky is more amusing if one is familiar with basics facts on distances in the universe and the notion of magnitude (the "size" of a star related to its brightness).

Hipparchus scale and comparison of magnitudes. At the distance of 10 pc the magnitude of Sun would be around 5.
Hipparchus scale and comparison of magnitudes. At the distance of 10 pc the magnitude of Sun would be around 5.

Distances in the universe

This article is consisted on three parts, devoted to distances in the universe, magnitudes and constellations. The hub firstly describes, in detail, units in astronomy: astronomical unit, light year and parsec. After that there are explanations about apparent and absolute stellar magnitude as the measures of stellar brightness. Finally, there is a note on astrognosy, branch of astronomy that deal with constellations.

Video: The article contains an breathtaking video, where one of the largest and most luminous star is compared by the whole Solar System. This star is Betelgeuse, the Orion's red supergiant star.

The spiral galaxy M31 known as Andromeda. Andromeda is the closest spiral galaxy  to the Milky Way.  It is the only other (besides the Milky Way) spiral galaxy that we can see with the naked eye.
The spiral galaxy M31 known as Andromeda. Andromeda is the closest spiral galaxy to the Milky Way. It is the only other (besides the Milky Way) spiral galaxy that we can see with the naked eye.
Saturn above the thick atmosphere of its moon Titan
Saturn above the thick atmosphere of its moon Titan

What one can find in Flysky's article on Astronomy and Astrophysics

  • a topic is presented systematically in the multimedia article

  • original images, drawn specially for the article
  • a carefully chosen video, up to around 3 minutes, that either summarize or enrich the topic

  • case study

  • quiz at the end of article, usually with 5 questions, that emphasize key points of the topic

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  • fast insight into the matter; provided by screening of images and its descriptions as well as emphasized titles or terms

  • enjoyable and interesting tales

The Solar System

Although planets are our first thought on the Sun System, our stellar system hides incredible wealth of other celestial bodies, its motions and its physical characteristics. In our stellar system there are great diversity of bodies: in addition to planets there are dwarf planets, planetoids, meteoroids, comets, meteors.

The development of knowledge about Sun System during history is not less interesting. Greek astronomers have devised ingenious techniques in order to get knowledge about Earth and the universe, like to determine the distance between the Sun and the Earth or to determine the size of the Earth.

The time after middle age, 16 and 17 century brings “quantum leap” in astronomy. Nicolaus Copernicus (1473-1543) published the work De revolutionibus orbium coelestium. In this book Copernicus proposes the heliocentric theory as an alternative theory to Ptolemy's geocentric model, with convincing arguments. Olaus Römer was a Danish astronomer who in 1676 made the first measurements of the speed of light. With this result it was ultimately clear that the speed of light is finite.

It could be argued that galaxies are discovered lately. The universe is full of galaxies, but we become aware of this in 20. century. It was done thankfully to the remarkable work of Edwin Hubble. E. Habble (1889-1953) was an American astronomer. The Hubble Telescope, which circulating in Earth's orbit providing better pictures than it would be possible from the Earth, is named in his honor.

The Solar System

The article firstly gives an overview on Galileo Galilei's observations from 1609. This work reveals crucial fact on the Solar System. A brief but systematic overview on celestial bodies present in the Solar System is done, which is illustrated with breathtaking photographs. At least, the hub describes discovery of the outer planets.

Video: The article contains a video with stunning pictures from Cassini orbiter when arriving at Saturn.The spacecraft Cassini was lunched from the Earth in 1997 towards Saturn.The journey to Saturn has taken 7 years.

Celestial Mechanics

Celestial mechanics is a branch of astronomy which tend to give answers on two questions: how celestial body moves and what is the cause of this motion.

It can be said that the central points of celestial mechanics are Kepler's laws of planetary motions and Newton's law of universal gravitation. The three Kepler's laws give mathematical description of motions in the Solar System which is the base of calculation of orbital elements of a celestial body. Newton's law explains why bodies move on the way of Kepler's law. Moreover, this fundamental law provides other useful calculation including free fall and the motion of satellites in an orbit.

In order to understand celestial mechanics, some foreknowledge in physics is needed. Firstly it is knowing of the three Newton axioms of mechanics, uniformly accelerated motion, circular motion and conservation laws.

Ellipse as the orbit of a planet. The size and the shape of an ellipse is defined by the eccentricity e and one of the semi-axes
Ellipse as the orbit of a planet. The size and the shape of an ellipse is defined by the eccentricity e and one of the semi-axes

Kepler's laws of planetary motion

This hub presents the three Kepler's laws. Johannes Kepler (1571-1630) was a German mathematician and astronomer, one of the greatest astronomers, who discovered fascinating laws underlying Earth's motion. Three Kepler's laws of planetary motion rule all motions in the Solar system as well as any planetary system. However, this discovery couldn't be made without a Danish astronomer Tycho Brahe (1546-1601). Brahe gave a great contribution with his accurate measurements of planetary positions.

Video: The article gives an animation of motions in the Sun System. There are orbits of inner and outer planets and some comets, including the Halley's comet. There is one more video, animating a planet's elliptical orbit around the Sun (illustration of the First and Second Kepler's low).

Case study: There are two case studies. The first one refer to the Jupiter system of moons. Based on the Europa's orbital period (the value that can be measured) we have to calculate the mass of Jupiter (the value that we can't measure directly). Second exercise is an analogy, here we deal with Uranus system.

There are three angular parameters that define a position along an orbit: the true anomaly f, the eccentric anomaly E and the mean anomaly M.
There are three angular parameters that define a position along an orbit: the true anomaly f, the eccentric anomaly E and the mean anomaly M.

Kepler's Equation

Kepler Equestin is the name of a mathematical relation that give the answer to the question: 'What is a position of the planet in a certain time since the last priapsis?' The article begins with a description of position parameters of a celestial body. Then, there is a precise instruction how to determine a body position along an orbit.

Video: The video shows an amazing animation of Halley's comet movements. Likewise, one can heard the basic facts about this comet.

Case study: There are two exercises in the hub, illustrating the matter. Having known orbital elements of the comet's ellipse around the Sun, one have to determine the orbital position vector and the true anomaly. The second exercise is about the Halley's comet. It should be calculated where the comet is at the moment.

Star
Type /position on HR
Spectral type
Betelgeuse
red supergiant
M2lb
Conopus
blue supergiant
F0lb
Alphard
orange bright giant
K3II
Vega
blue-white dwarf
A0V
Sirius
white dwarf
A1V
Sun
yellow dwarf
G2V
Some known stars, its spectral type and position on HR diagram

Stellar physics

The term stellar physics usually refers to the stellar evolution, star formation, star structure and similar topics. The understanding of this phenomena requieres a significant part of modern physics, including atomic and nuclear physics, solid state theory and hydrodynamics.

The central place in the theory of stellar evolution takes the Hertzsprung–Russell diagram (HR diagram), that shows physical characteristics of stars. Stars are position on the diagram depending on its brightness and luminosity.

Magnitude and velocity for the star Delta Cephei.
Magnitude and velocity for the star Delta Cephei.

Cepheid varaiable stars – candles in the universe


Did you know that variable stars took an important role in the discovery of galaxies? Namely, this kind of stars provides a method for calculation of the distances, based on period-luminosity relationship. The hub describes pulsation variables in details and gives an overview on the other types of these stars.

Video: The article is equipped with an animation of Chi Cygni, a 408-day pulsating star. Chi Cygnus is a variable star of the Mira type in the constellation Cygnus.

Case study: Interestingly, in spite of the complexity of processes in a star that cause the variation in brightness, pure brightness oscillation behaves as an pendulum. Based on this fact, we calculate the density of a given star.


Close binaries appear in three main forms: detached, semidetached and contact binary stars
Close binaries appear in three main forms: detached, semidetached and contact binary stars

The Paradox of Binary Stars


The hub is very detailed review of the binary stars. It begins with kinematics of a binary system, that is the physics underlined binary stars motion. Furthermore, one can read about the genesis of binary stars and its classification. Finally there is a paragraph about mass determination within this type of celestial bodies.

Video: The matter is enrich with two animations. The first one is animation of the Earth-Moon binary system while the other represents an eclipsing binary star.



The video below shows some stunning pictures of planets nebula, galaxies.. The photographs are made by the Hubble Space Telescope.

The Milky Way Poster, 2nd Edition
The Milky Way Poster, 2nd Edition

The Milky Way, our galaxy. The poster presents reconstruction, since it couldn't be photographed. The Milky Way is a spiral galaxy with diameter around 100000 light-years and with 200-400 billion stars.

 

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