Physics Talk

Saya Kimura:  https://www.pexels.com/photo/bright-clear-close-up-dark-401107/ 3 x 10 8 ms -1 . This is a value ingrained into the minds of all physicists: the speed of light (to one significant figure). Special relativity reveals that this is the ultimate speed limit of the universe. However, in the past, many believed that light propagates instantaneously. Danish astronomer, Ole Rømer, made the first quantitative measurement of the speed of light in 1676, demonstrating that light travels at a finite speed. The Earth, the Sun and Jupiter Rømer noticed that the distance between the Earth and Jupiter affected the time at which Io, the gas giant’s innermost moon, seemed to emerge. [1] When the Earth is closest to Jupiter in its orbit around the Sun, Io appeared from behind Jupiter earlier than expected. Meanwhile, when Earth was at its farthest point from Jupiter, Io emerged later than expected. [1] Light took longer to travel from Io to the Earth when the distance between the...

Pbroks13 / Public domain; https://commons.wikimedia.org/wiki/File:Doppler_effect.svg ‘It may […] be more than apt to call the Doppler Effect […] the effect of the millennium.’ – Anton Zeilinger, Wolf Prize in Physics recipient and President of the Austrian Academy of Sciences, July 2007. Have you ever noticed how the pitch of a passing ambulance siren seems to change? This is the Doppler effect at work: the observed frequency of a wave depends on the relative motion of the source and detector.   Picture ripples on the surface of a pond after a pebble has been cast, where the circular wavefronts are equally separated. Since a wave’s velocity is determined by the medium through which it propagates, the wavefronts travel at a fixed speed. Now imagine a duck is swimming in the pond. The wavefronts created are no longer evenly spaced because the centre of each new wavefront is slightly displaced in the direction of travel. If it approaches an unmoving swan, from the swan’s persp...

NASA/SpaceX / Public domain;  https://commons.wikimedia.org/wiki/File:SpaceX_Crew_Dragon_(More_cropped).jpg Today, on the 30th of May 2020, experienced US astronauts Bob Behnken and Doug Herley will be launched into orbit. Their mission to the International Space Station, known as Crew Demo-2, will make them the first astronauts to launch from American soil in almost a decade. It will also be the first manned space mission for SpaceX. The company was founded in 2002 by Elon Musk who has previously promised to send paying customers into orbit sparking a new era of space tourism. [1] His long-term goals for the company include the colonisation of Mars. [2] Resurrection In 2011, NASA officially retired its 30-year Space Shuttle Program. Many believe that a successful SpaceX mission would ‘resurrect the US's human spaceflight capabilities and open a new era of commercial space exploration.’ [3] NASA’s decision to retire the programme was motivated by its plans to ‘devote its res...

Zouavman Le Zouave / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0); https://commons.wikimedia.org/wiki/File:Light_shining1.JPG The Rayleigh-Jeans law, based on classical physics, gives the spectral radiance (linked to intensity) of blackbody electromagnetic radiation as a function of wavelength: B v (T) is spectral radiance; k B is the Boltzmann constant; T is temperature; c is the speed of light; λ is wavelength. [1] Blackbodies are defined as ‘[idealised] objects that perfectly absorb and then re-emit radiation’ [2] . The equation shows that increasing the wavelength should cause the spectral radiance of the emitted radiation to decrease and tend to zero whilst decreasing wavelength causes it to increase, tending to infinity. This graph [3] shows what the Rayleigh-Jeans law predicts (labelled ‘Classical theory’) and what actually happens at different temperatures (the blue, green and red lines). Although the law seems to coincide with exper...

https://commons.wikimedia.org/wiki/File:Impact_event.jpg In Part 1 ( phys-talk.blogspot.com/2020/03/planetary-defence-part-1-introduction.html ), I looked at the impacts of asteroids and comets and how to distinguish between them. The first step to protecting our planet from potentially dangerous asteroid and comet attacks is detection. This allows scientists to predict whether an object poses a threat to the Earth through orbit determination. If a hazardous near-earth object is found, the next step is the ‘implementation of measures to deflect or disrupt’ it. [1]   Detection The main method of detecting near-earth objects is through telescope observations. For instance, NASA currently supports ‘several ground-based observatories that scan the skies for asteroids’ (e.g. the Catalina Sky Survey in Arizona) [2] as part of its ‘Near-Earth Observation Program.’ At these observatories, the sky is scanned and images are taken where an asteroid, which reflects...

E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria (http://www.sternwarte.at) / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) The Chicxulub Crater in Mexico, spanning over 110 miles in width, marks the spot where, 66 million years ago, 'an asteroid the size of a mountain' [1] struck the Earth. The asteroid travelled at a speed of around 40,000 miles per hour [1] before pummelling the planet with an 'explosive yield estimated at 100 trillion tons of TNT.' [1] This is 'two million times stronger than the most powerful man-made bomb’ [2] . The immense impact of the asteroid is believed to have caused mass extinction including that of the dinosaurs.  Although they are rare occurrences, scientists have tried to find ways to protect the planet from asteroid and comet attacks which could potentially have devastating consequences as shown by the dinosaur-ending event 66 million years ago.   Asteroids vs Comets Asteroids are ...

Picture credits: X-ray: NASA/CXC/Naval Research Lab/Giacintucci, S.; XMM:ESA/XMM; Radio: NCRA/TIFR/GMRTN; Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSF Astronomers have detected the 'biggest explosion since the big bang' using high power telescopes: NASA's Chandra X-ray Observatory, the ESA's XMM-Newton, the Giant Metrewave Radio Telescope in India and the Murchison Widefield Array in Australia. This explosion has easily surpassed the previous record held by an eruption from a cluster named MS 0735.6+7421 in which 'a mass of about 300 million Suns was swallowed'. This latest outburst is said to be 'five times bigger than any other known explosion'. Calculations suggest that approximately 5 x 10 54  Joules of energy would be required to cause an explosion of this magnitude. The calculated amount of energy involved is around 9 x 10 33  times more than annual global energy consumption (5.8 x 10 20  Joules). The explosion was ...