In mathematics, a Fourier series decomposes periodic functions or periodic signals into the sum of a (possibly infinite) set of simple oscillating functions, namely sines and cosines (or complex exponentials).
You can see below a nice visualisation of an approximation of a square wave by taking the first 1, 2, 3 and 4 terms of its Fourier series.
► An interactive animation can be seen here>>
► Gif source>> https://en.wikipedia.org/wiki/File:Fourier_series_square_wave_circles_animation.gif
#mathematics, #animation, #FourierSeries, #squarewave
Robert's Quartet is a family of four very different galaxies, located at a distance of about 160 million light-years, close to the centre of the southern constellation of the Phoenix.
Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel in the 1830s.
NGC 87 (upper right) is an irregular galaxy similar to the satellites of our Milky Way, the Magellanic Clouds.
NGC 8 (centre) is a spiral galaxy with an external diffuse envelope, most probably composed of gas.
NGC 89 (lower middle) is another spiral galaxy with two large spiral arms.
The largest member of the system, NGC 92 (left), is a spiral Sa galaxy with an unusual appearance. One of its arms, about 100,000 light-years long, has been distorted by interactions and contains a large quantity of dust.
The galaxies of Robert's Quartet are crowded into a space just 150,000 light years across – only 1.5 times the width of our own galaxy, the Milky Way. This proximity makes them one of the best known examples of a compact group of galaxies, whose members gravitationally disturb each other.
Because such groups contain four to eight galaxies in a very small region, they are excellent laboratories for the study of galactic interactions and their effects, in particular on the formation of stars.
The image is based on data collected with the FORS2 multi-mode instrument on ESO's Very Large Telescope.
► Credit: ESO
Further reading and references
► Cosmic Portrait of a Perturbed Family>> https://www.eso.org/public/news/eso0535/
► Robert's Quartet>>
► Galaxy Classification>>
► Robert's Quartet>> https://en.wikipedia.org/wiki/Robert's_Quartet
#Universe, # GalaxyInteraction, #Galaxies, #RobertsQuartet, #Astronomy, #Space
A star's life cycle is determined by its mass. The larger its mass, the shorter its life cycle. A star's mass is determined by the amount of matter that is available in its nebula, the giant cloud of gas and dust from which it was born. Over time, the hydrogen gas in the nebula is pulled together by gravity and it begins to spin.
As the gas spins faster, it heats up and becomes as a protostar. Eventually the temperature reaches 15,000,000 degrees and nuclear fusion occurs in the cloud's core. The cloud begins to glow brightly, contracts a little, and becomes stable. It is now a main sequence star and will remain in this stage, shining for millions to billions of years to come. This is the stage our Sun is at right now.
As the main sequence star glows, hydrogen in its core is converted into helium by nuclear fusion. When the hydrogen supply in the core begins to run out, and the star is no longer generating heat by nuclear fusion, the core becomes unstable and contracts. The outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and glows red. The star has now reached the red giant phase. It is red because it is cooler than it was in the main sequence star stage and it is a giant because the outer shell has expanded outward. In the core of the red giant, helium fuses into carbon.
All stars evolve the same way up to the red giant phase. The amount of mass a star has determines which of the following life cycle paths it will take from there.
For low mass stars, after the helium has fused into carbon, the core collapses again. As the core collapses, the outer layers of the star are expelled. A planetary nebula is formed by the outer layers. The core remains as a white dwarf and eventually cools to become a black dwarf.
High mass stars are born in nebulae and evolve and live in the Main Sequence. However their life cycles start to differ after the red giant phase. A massive star will undergo a supernova explosion. If the remnant of the explosion is 1.4 to about 3 times as massive as our Sun, it will become a neutron star. The core of a massive star that has more than roughly 3 times the mass of our Sun after the explosion will do something quite different. The force of gravity overcomes the nuclear forces which keep protons and neutrons from combining. The core is thus swallowed by its own gravity. It has now become a black hole which readily attracts any matter and energy that comes near it.
What happens between the red giant phase and the supernova explosion?
Once stars that are 5 times or more massive than our Sun reach the red giant phase, their core temperature increases as carbon atoms are formed from the fusion of helium atoms. Gravity continues to pull carbon atoms together as the temperature increases and additional fusion processes proceed, forming oxygen, nitrogen, and eventually iron.
When the core contains essentially just iron, fusion in the core ceases. This is because iron is the most compact and stable of all the elements. It takes more energy to break up the iron nucleus than that of any other element. Creating heavier elements through fusing of iron thus requires an input of energy rather than the release of energy. Since energy is no longer being radiated from the core, in less than a second, the star begins the final phase of gravitational collapse. The core temperature rises to over 100 billion degrees as the iron atoms are crushed together. The repulsive force between the nuclei overcomes the force of gravity, and the core recoils out from the heart of the star in a shock wave, which we see as a supernova explosion.
#universe #space #stars #science #nasa
Arecibo and Goldston planetary radar observations of 250 m asteroid (226514) 2003 UX34 reveal it is a binary system!
The Minor Planet Center has classified 2003 UX34 as a "Potentially Hazardous Asteroid."
This gif demonstrates the orbit of the secondary object about the primary; each frame is a sum of 3 minutes of data.
NEA 2003 UX34 was discovered in October 2003 by Spacewatch at Kitt Peak. At its closest approach on January 2, 2017, it was within a distance 19 times the Earth-Moon distance.
► Source>> http://www.naic.edu/~pradar/
► Goldstone Radar Observations Planning: 2003 UX34>>
#SolarSystem, #Asteroid , #AreciboPlanetaryRadar , #2265142003UX34, #NearEarthAsteroids
This weekend marks the 75th birthday of renowned physicist Stephen Hawking. Considered to be one of the most popular scientists of all-time (after Albert Einstein), Hawking’s contributions to the understanding of gravity parallel none other than perhaps Einstein and Roger Penrose. Sir Martin Rees, Royal Astronomer, wrote of Hawking: “His most remarkable single discovery, black‐hole evaporation, came in 1974. But that was itself just the impetus for a crescendo of achievement that continues to this day.”
Hawking in A Brief History of Time has ably traversed the barrier between complex scientific theories and public engagement with a range of subjects within cosmology. The Big Bang, black holes, light cones, space, and time had all long held the public’s attention through the advent of science-fiction writing and movies, but with this book the science behind each theory was made accessible to non-specialists.
The beautiful Andromeda Galaxy is often imaged by planet Earth-based astronomers. Also known as M31, the nearest large spiral galaxy is a familiar sight with dark dust lanes, bright yellowish core, and spiral arms traced by blue starlight. A mosaic of well-exposed broad and narrow-band image data, this colorful, premier portrait of our neighboring island universe offers strikingly unfamiliar features though, faint reddish clouds of glowing ionized hydrogen gas in the same wide field of view.
Still, the ionized hydrogen clouds likely lie in the foreground of the scene, well within our Milky Way Galaxy. They could be associated with the pervasive, dusty interstellar cirrus clouds scattered hundreds of light-years above our own galactic plane. If they were located at the 2.5 million light-year distance of the Andromeda Galaxy they would be enormous, since the Andromeda Galaxy itself is 200,000 or so light-years across.
Image and info via APOD
Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)
#space #nasa #andromeda #science #exploration
- Istituto Tecnico Industriale CelliniInformatica, Elettronica, Elettrotecnica, 2013 - present
- CSL ToscanaReti, Linux, Java, HTML, SQL, 2005 - 2010
- Università di FirenzeMatematica, Informatica, Fisica, 2001 - 2009
- Liceo Scientifico Rodolico1996 - 2001
- Scuola Media Ghiberti1993 - 1996
- Scuola Elementare Don Milani1988 - 1993
- M|M ComunicazioneProgrammatore di siti Internet, 2011 - 2011
- NegensAmministratore di Sistema, 2010 - 2010
- SoftecTecnico di rete, 2006 - 2006
Via Vittorio Corcos 25, Firenze
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