Posted on by Matt Williams

How Does Light Travel?

Light moves at different wavelengths, represented here by the different colors seen in a prism. Credit: NASA and ESA

Ever since Democritus – a Greek philosopher who lived between the 5th and 4th century’s BCE – argued that all of existence was made up of tiny indivisible atoms, scientists have been speculating as to the true nature of light. Whereas scientists ventured back and forth between the notion that light was a particle or a wave until the modern era, the 20th century led to breakthroughs that showed us that it behaves as both.

These included the discovery of the electron, the development of quantum theory, and Einstein’s Theory of Relativity. However, there remains many unanswered questions about light, many of which arise from its dual nature. For instance, how is it that light can be apparently without mass, but still behave as a particle? And how can it behave like a wave and pass through a vacuum, when all other waves require a medium to propagate?

Theory of Light to the 19th Century:

During the Scientific Revolution, scientists began moving away from Aristotelian scientific theories that had been seen as accepted canon for centuries. This included rejecting Aristotle’s theory of light, which viewed it as being a disturbance in the air (one of his four “elements” that composed matter), and embracing the more mechanistic view that light was composed of indivisible atoms.

In many ways, this theory had been previewed by atomists of Classical Antiquity – such as Democritus and Lucretius – both of whom viewed light as a unit of matter given off by the sun. By the 17th century, several scientists emerged who accepted this view, stating that light was made up of discrete particles (or “corpuscles”). This included Pierre Gassendi, a contemporary of René Descartes, Thomas Hobbes, Robert Boyle, and most famously, Sir Isaac Newton.

The first edition of Newton's Opticks: or, a treatise of the reflexions, refractions, inflexions and colours of light (1704). Credit: Public Domain.
The first edition of Newton’s Opticks: or, a treatise of the reflexions, refractions, inflexions and colours of light (1704). Credit: Public Domain.

Newton’s corpuscular theory was an elaboration of his view of reality as an interaction of material points through forces. This theory would remain the accepted scientific view for more than 100 years, the principles of which were explained in his 1704 treatise “Opticks, or, a Treatise of the Reflections, Refractions, Inflections, and Colours of Light“. According to Newton, the principles of light could be summed as follows:

  • Every source of light emits large numbers of tiny particles known as corpuscles in a medium surrounding the source.
  • These corpuscles are perfectly elastic, rigid, and weightless.

This represented a challenge to “wave theory”, which had been advocated by 17th century Dutch astronomer Christiaan Huygens. . These theories were first communicated in 1678 to the Paris Academy of Sciences and were published in 1690 in his “Traité de la lumière“ (“Treatise on Light“). In it, he argued a revised version of Descartes views, in which the speed of light is infinite and propagated by means of spherical waves emitted along the wave front.

Double-Slit Experiment:

By the early 19th century, scientists began to break with corpuscular theory. This was due in part to the fact that corpuscular theory failed to adequately explain the diffraction, interference and polarization of light, but was also because of various experiments that seemed to confirm the still-competing view that light behaved as a wave.

The most famous of these was arguably the Double-Slit Experiment, which was originally conducted by English polymath Thomas Young in 1801 (though Sir Isaac Newton is believed to have conducted something similar in his own time). In Young’s version of the experiment, he used a slip of paper with slits cut into it, and then pointed a light source at them to measure how light passed through it.

According to classical (i.e. Newtonian) particle theory, the results of the experiment should have corresponded to the slits, the impacts on the screen appearing in two vertical lines. Instead, the results showed that the coherent beams of light were interfering, creating a pattern of bright and dark bands on the screen. This contradicted classical particle theory, in which particles do not interfere with each other, but merely collide.

The only possible explanation for this pattern of interference was that the light beams were in fact behaving as waves. Thus, this experiment dispelled the notion that light consisted of corpuscles and played a vital part in the acceptance of the wave theory of light. However subsequent research, involving the discovery of the electron and electromagnetic radiation, would lead to scientists considering yet again that light behaved as a particle too, thus giving rise to wave-particle duality theory.

Electromagnetism and Special Relativity:

Prior to the 19th and 20th centuries, the speed of light had already been determined. The first recorded measurements were performed by Danish astronomer Ole Rømer, who demonstrated in 1676 using light measurements from Jupiter’s moon Io to show that light travels at a finite speed (rather than instantaneously).

Prof. Albert Einstein uses the blackboard as he delivers the 11th Josiah Willard Gibbs lecture at the meeting of the American Association for the Advancement of Science in the auditorium of the Carnegie Institue of Technology Little Theater at Pittsburgh, Pa., on Dec. 28, 1934. Using three symbols, for matter, energy and the speed of light respectively, Einstein offers additional proof of a theorem propounded by him in 1905 that matter and energy are the same thing in different forms. (AP Photo)
Prof. Albert Einstein delivering the 11th Josiah Willard Gibbs lecture at the meeting of the American Association for the Advancement of Science on Dec. 28th, 1934. Credit: AP Photo

By the late 19th century, James Clerk Maxwell proposed that light was an electromagnetic wave, and devised several equations (known as Maxwell’s equations) to describe how electric and magnetic fields are generated and altered by each other and by charges and currents. By conducting measurements of different types of radiation (magnetic fields, ultraviolet and infrared radiation), he was able to calculate the speed of light in a vacuum (represented as c).

In 1905, Albert Einstein published “On the Electrodynamics of Moving Bodies”, in which he advanced one of his most famous theories and overturned centuries of accepted notions and orthodoxies. In his paper, he postulated that the speed of light was the same in all inertial reference frames, regardless of the motion of the light source or the position of the observer.

Exploring the consequences of this theory is what led him to propose his theory of Special Relativity, which reconciled Maxwell’s equations for electricity and magnetism with the laws of mechanics, simplified the mathematical calculations, and accorded with the directly observed speed of light and accounted for the observed aberrations. It also demonstrated that the speed of light had relevance outside the context of light and electromagnetism.

For one, it introduced the idea that major changes occur when things move close the speed of light, including the time-space frame of a moving body appearing to slow down and contract in the direction of motion when measured in the frame of the observer. After centuries of increasingly precise measurements, the speed of light was determined to be 299,792,458 m/s in 1975.

Einstein and the Photon:

In 1905, Einstein also helped to resolve a great deal of confusion surrounding the behavior of electromagnetic radiation when he proposed that electrons are emitted from atoms when they absorb energy from light. Known as the photoelectric effect, Einstein based his idea on Planck’s earlier work with “black bodies” – materials that absorb electromagnetic energy instead of reflecting it (i.e. white bodies).

At the time, Einstein’s photoelectric effect was attempt to explain the “black body problem”, in which a black body emits electromagnetic radiation due to the object’s heat. This was a persistent problem in the world of physics, arising from the discovery of the electron, which had only happened eight years previous (thanks to British physicists led by J.J. Thompson and experiments using cathode ray tubes).

At the time, scientists still believed that electromagnetic energy behaved as a wave, and were therefore hoping to be able to explain it in terms of classical physics. Einstein’s explanation represented a break with this, asserting that electromagnetic radiation behaved in ways that were consistent with a particle – a quantized form of light which he named “photons”. For this discovery, Einstein was awarded the Nobel Prize in 1921.

Wave-Particle Duality:

Subsequent theories on the behavior of light would further refine this idea, which included French physicist Louis-Victor de Broglie calculating the wavelength at which light functioned. This was followed by Heisenberg’s “uncertainty principle” (which stated that measuring the position of a photon accurately would disturb measurements of it momentum and vice versa), and Schrödinger’s paradox that claimed that all particles have a “wave function”.

In accordance with quantum mechanical explanation, Schrodinger proposed that all the information about a particle (in this case, a photon) is encoded in its wave function, a complex-valued function roughly analogous to the amplitude of a wave at each point in space. At some location, the measurement of the wave function will randomly “collapse”, or rather “decohere”, to a sharply peaked function. This was illustrated in Schrödinger famous paradox involving a closed box, a cat, and a vial of poison (known as the “Schrödinger Cat” paradox).

In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect. The animation below shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet
Artist’s impression of two photons travelling at different wavelengths, resulting in different- colored light. Credit: NASA/Sonoma State University/Aurore Simonnet

According to his theory, wave function also evolves according to a differential equation (aka. the Schrödinger equation). For particles with mass, this equation has solutions; but for particles with no mass, no solution existed. Further experiments involving the Double-Slit Experiment confirmed the dual nature of photons. where measuring devices were incorporated to observe the photons as they passed through the slits.

When this was done, the photons appeared in the form of particles and their impacts on the screen corresponded to the slits – tiny particle-sized spots distributed in straight vertical lines. By placing an observation device in place, the wave function of the photons collapsed and the light behaved as classical particles once more. As predicted by Schrödinger, this could only be resolved by claiming that light has a wave function, and that observing it causes the range of behavioral possibilities to collapse to the point where its behavior becomes predictable.

The development of Quantum Field Theory (QFT) was devised in the following decades to resolve much of the ambiguity around wave-particle duality. And in time, this theory was shown to apply to other particles and fundamental forces of interaction (such as weak and strong nuclear forces). Today, photons are part of the Standard Model of particle physics, where they are classified as boson – a class of subatomic particles that are force carriers and have no mass.

So how does light travel? Basically, traveling at incredible speeds (299 792 458 m/s) and at different wavelengths, depending on its energy. It also behaves as both a wave and a particle, able to propagate through mediums (like air and water) as well as space. It has no mass, but can still be absorbed, reflected, or refracted if it comes in contact with a medium. And in the end, the only thing that can truly divert it, or arrest it, is gravity (i.e. a black hole).

What we have learned about light and electromagnetism has been intrinsic to the revolution which took place in physics in the early 20th century, a revolution that we have been grappling with ever since. Thanks to the efforts of scientists like Maxwell, Planck, Einstein, Heisenberg and Schrodinger, we have learned much, but still have much to learn.

For instance, its interaction with gravity (along with weak and strong nuclear forces) remains a mystery. Unlocking this, and thus discovering a Theory of Everything (ToE) is something astronomers and physicists look forward to. Someday, we just might have it all figured out!

We have written many articles about light here at Universe Today. For example, here’s How Fast is the Speed of Light?, How Far is a Light Year?, What is Einstein’s Theory of Relativity?

If you’d like more info on light, check out these articles from The Physics Hypertextbook and NASA’s Mission Science page.

We’ve also recorded an entire episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.

Posted on by Matt Williams

Friendly Giants Have Cozy Habitable Zones Too

Artist's impression of a red giant star. If the star is in a binary pair, what happens to its sibling? Credit:NASA/ Walt Feimer

It is an well-known fact that all stars have a lifespan. This begins with their formation, then continues through their Main Sequence phase (which constitutes the majority of their life) before ending in death. In most cases, stars will swell up to several hundred times their normal size as they exit the Main Sequence phase of their life, during which time they will likely consume any planets that orbit closely to them.

However, for planets that orbit the star at greater distances (beyond the system’s “Frost Line“, essentially), conditions might actually become warm enough for them to support life. And according to new research which comes from the Carl Sagan Institute at Cornell University, this situation could last for some star systems into the billions of years, giving rise to entirely new forms of extra-terrestrial life!

In approximately 5.4 billion years from now, our Sun will exit its Main Sequence phase. Having exhausted the hydrogen fuel in its core, the inert helium ash that has built up there will become unstable and collapse under its own weight. This will cause the core to heat up and get denser, which in turn will cause the Sun to grow in size and enter what is known as the Red Giant-Branch (RGB) phase of its evolution.

The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser
The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser

This period will begin with our Sun becoming a subgiant, in which it will slowly double in size over the course of about half a billion years. It will then spend the next half a billion years expanding more rapidly, until it is 200 times its current size and several thousands times more luminous. It will then officially be a red giant star, eventually expanding to the point where it reaches beyond Mars’ orbit.

As we explored in a previous article, planet Earth will not survive our Sun becoming a Red Giant – nor will Mercury, Venus or Mars. But beyond the “Frost Line”, where it is cold enough that volatile compounds – such as water, ammonia, methane, carbon dioxide and carbon monoxide – remain in a frozen state, the remain gas giants, ice giants, and dwarf planets will survive. Not only that, but a massive thaw will set in.

In short, when the star expands, its “habitable zone” will likely do the same, encompassing the orbits of Jupiter and Saturn. When this happens, formerly uninhabitable places – like the Jovian and Cronian moons – could suddenly become inhabitable. The same holds true for many other stars in the Universe, all of which are fated to become Red Giants as they near the end of their lifespans.

However, when our Sun reaches its Red Giant Branch phase, it is only expected to have 120 million years of active life left. This is not quite enough time for new lifeforms to emerge, evolve and become truly complex (i.e. like humans and other species of mammals). But according to a recent research study that appeared in The Astrophysical Journal – titled “Habitable Zone of Post-Main Sequence Stars” – some planets may be able to remain habitable around other red giant stars in our Universe for much longer – up to 9 billion years or more in some cases!

Ramses Ramirez, left, and Lisa Kaltenegger hold a replica of our own habitable world, as they hunt for other places in the universe where life can thrive. Credit: Chris Kitchen/University Photo
Ramses Ramirez (left) and Lisa Kaltenegger are on the hunt for other places in the universe where life can thrive. Credit: Chris Kitchen/University Photo

To put that in perspective, nine billion years is close to twice the current age of Earth. So assuming that the worlds in question also have the right mix of elements, they will have ample time to give rise to new and complex forms of life. The study’s co-author, Professor Lisa Kaltennegeris, is also the director of the Carl Sagan Institute. As such, she is no stranger to searching for life in other parts of the Universe. As she explained to Universe Today via email:

“We found that planets – depending on how big their Sun is (the smaller the star, the longer the planet can stay habitable) – can stay nice and warm for up to 9 Billion years. That makes an old star an interesting place to look for life. It could have started sub-surface (e.g. in a frozen ocean) and then when the ice melts, the gases that life breaths in and out can escape into the atmosphere – what allows astronomers to pick them up as signatures of life. Or for the smallest stars, the time a formerly frozen planet can be nice and warm is up to 9 billion years. Thus life could potentially even get started in that time.”

Using existing models of stars and their evolution – i.e. one-dimensional radiative-convective climate and stellar evolutionary models – for their study, Kaltenegger and Ramirez were able to calculate the distances of the habitable zones (HZ) around a series of post-Main Sequence (post-MS) stars. Ramses M. Ramirez – a research associate at the Carl Sagan Institute and the lead author of the paper – explained the research process to Universe Today via email:

“We used stellar evolutionary models that tell us how stellar quantities, mainly the brightness, radius, and temperature all change with time as the star ages through the red giant phase. We also used a  climate model to then compute how much energy each star is outputting at the boundaries of the habitable zone. Knowing this and the stellar brightness mentioned above, we can compute the distances to these habitable zone boundaries.”

After several billions years, yellow suns (like ours) become Red Giants, expanding to several hundred times their normal size. Credit: Wendy Kenigsburg
After several billions years, yellow suns (like ours) become Red Giants, expanding to several hundred times their normal size. Credit: Wendy Kenigsburg

At the same time, they considered how this kind of stellar evolution could effect the atmosphere of the star’s planets. As a star expands, it loses mass and ejects it outward in the form of solar wind. For planets that orbit close to a star, or those that have low surface gravity, they may find some or all of their atmospheres blasted away. On the other hand, planets with sufficient mass (or positioned at a safe distance) could maintain most of their atmospheres.

“The stellar winds from this mass loss erodes planetary atmospheres, which we also compute as a function of time,” said Ramirez. “As the star loses mass, the solar system conserves angular momentum by moving outwards. So, we also take into account how the orbits move out with time.” By using models that incorporated the rate of stellar and atmospheric loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases of star, they were able to determine how this would play out for planets that ranged in size from super-Moons to super-Earths.

What they found was that a planet can stay in a post-HS HZ for eons or more, depending on how hot the star is, and figuring for metallicities that are similar to our Sun’s. As Ramirez explained:

“The main result is that the maximum time that a planet can remain in this red giant habitable zone of hot stars is 200 million years. For our coolest star (M1), the maximum time a planet can stay within this red giant habitable zone is 9 billion years. Those results assume metallicity levels similar to those of our Sun. A star with a higher percentage of metals takes longer to fuse the non-metals (H, He..etc) and so these maximum times can increase some more, up to about a factor of two.”

Europa's cracked, icy surface imaged by NASA's Galileo spacecraft in 1998. Credit: NASA/JPL-Caltech/SETI Institute.
Could Europa’s cracked, icy surface thaw and give rise to a new habitable world when our Sun becomes a Red Giant in a few billion years? Credit: NASA/JPL-Caltech/SETI Institute

Within the context of our Solar System, this could mean that in a few billion years, worlds like Europa and Enceladus (which are already suspected of having life beneath their icy surfaces) might get a shot at becoming full-fledged habitable worlds. As Ramirez summarized beautifully:

“This means that the post-main-sequence is another potentially interesting phase of stellar evolution from a habitability standpoint. Long after the inner system of planets have been turned into sizzling wastelands by the expanding, growing red giant star, there could be potentially habitable abodes farther away from the chaos. If they are frozen worlds, like Europa, the ice would melt, potentially unveiling any preexisting life. Such pre-existing life may be detectable by future missions/telescopes looking for atmospheric biosignatures.”

But perhaps the most exciting take-away from their research study was their conclusion that planets orbiting within their star’s post-MS habitable zones would be doing so at distances that would make them detectable using direct imaging techniques. So not only are the odds of finding life around older stars better than previously thought, we should have no trouble in spotting them using current exoplanet-hunting techniques!

It is also worth noting that Kaltenegger and Dr. Ramirez have submitted a second paper for publication, in which they provide a list of 23 red giant stars within 100 light-years of Earth. Knowing that these stars, all of which are in our stellar neighborhood, could have life-sustaining worlds within their habitable zones should provide additional opportunities for planet hunters in the coming years.

And be sure to check out this video from Cornellcast, where Prof. Kaltenegger shares what inspires her scientific curiosity and how Cornell’s scientists are working to find proof of extra-terrestrial life.

Further Reading: The Astrophysical Journal

Posted on by Matt Williams

What Is Air Resistance?

Space Travel
Atlantis Breaks Through the Clouds

Here on Earth, we tend to take air resistance (aka. “drag”) for granted. We just assume that when we throw a ball, launch an aircraft, deorbit a spacecraft, or fire a bullet from a gun, that the act of it traveling through our atmosphere will naturally slow it down. But what is the reason for this? Just how is air able to slow an object down, whether it is in free-fall or in flight?

Because of our reliance on air travel, our enthusiasm for space exploration, and our love of sports and making things airborne (including ourselves), understanding air resistance is key to understanding physics, and an integral part of many scientific disciplines. As part of the subdiscipline known as fluid dynamics, it applies to fields of aerodynamics, hydrodynamics, astrophysics, and nuclear physics (to name a few).

Definition:

By definition, air resistance describes the forces that are in opposition to the relative motion of an object as it passes through the air. These drag forces act opposite to the oncoming flow velocity, thus slowing the object down. Unlike other resistance forces, drag depends directly on velocity, since it is the component of the net aerodynamic force acting opposite to the direction of the movement.

Another way to put it would be to say that air resistance is the result of collisions of the object’s leading surface with air molecules. It can therefore be said that the two most common factors that have a direct effect upon the amount of air resistance are the speed of the object and the cross-sectional area of the object. Ergo, both increased speeds and cross-sectional areas will result in an increased amount of air resistance.

This picture shows a bullet and the air flowing around it, giving visual representation to air resistance. Credits: Andrew Davidhazy/Rochester Institute of Technology
Picture showing a bullet and the air flowing around it, giving visual representation to air resistance. Credits: Andrew Davidhazy/Rochester Institute of Technology

In terms of aerodynamics and flight, drag refers to both the forces acting opposite of thrust, as well as the forces working perpendicular to it (i.e. lift). In astrodynamics, atmospheric drag is both a positive and a negative force depending on the situation. It is both a drain on fuel and efficiency during lift-off and a fuel savings when a spacecraft is returning to Earth from orbit.

Calculating Air Resistance:

Air resistance is usually calculated using the “drag equation”, which determines the force experienced by an object moving through a fluid or gas at relatively large velocity. This can be expressed mathematically as:

F_D\, =\, \tfrac12\, \rho\, v^2\, C_D\, A

In this equation, FD represents the drag force, p is the density of the fluid, v is the speed of the object relative to sound, A is the cross-section area, and CD is the the drag coefficient. The result is what is called “quadratic drag”. Once this is determined, calculating the amount of power needed to overcome the drag involves a similar process, which can be expressed mathematically as:

P_d = \mathbf{F}_d \cdot \mathbf{v} = \tfrac12 \rho v^3 A C_d

Here, Pd is the power needed to overcome the force of drag, Fd is the drag force, v is the velocity, p is the density of the fluid, v is the speed of the object relative to sound, A is the cross-section area, and Cd is the the drag coefficient. As it shows, power needs are the cube of the velocity, so if it takes 10 horsepower to go 80 kph, it will take 80 horsepower to go 160 kph. In short, a doubling of speed requires an application of eight times the amount of power.

An F-22 Raptor reaching a velocity high enough to achieve a sonic boom. Credit: strangesounds.org
An F-22 Raptor reaching a velocity high enough to achieve a sonic boom. Credit: strangesounds.org

Types of Air Resistance:

There are three main types of drag in aerodynamics – Lift Induced, Parasitic, and Wave. Each affects an objects ability to stay aloft as well as the power and fuel needed to keep it there. Lift induced (or just induced) drag occurs as the result of the creation of lift on a three-dimensional lifting body (wing or fuselage). It has two primary components: vortex drag and lift-induced viscous drag.

The vortices derive from the turbulent mixing of air of varying pressure on the upper and lower surfaces of the body. These are needed to create lift. As the lift increases, so does the lift-induced drag. For an aircraft this means that as the angle of attack and the lift coefficient increase to the point of stall, so does the lift-induced drag.

By contrast, parasitic drag is caused by moving a solid object through a fluid. This type of drag is made up of multiple components, which includes “form drag” and “skin friction drag”. In aviation, induced drag tends to be greater at lower speeds because a high angle of attack is required to maintain lift, so as speed increases this drag becomes much less, but parasitic drag increases because the fluid is flowing faster around protruding objects increasing friction. The combined overall drag curve is minimal at some airspeeds and will be at or close to its optimal efficiency.

Space Shuttle Columbia launching on its maiden voyage on April 12th, 1981. Credit: NASA
Space Shuttle Columbia launching on its maiden voyage on April 12th, 1981. Credit: NASA

Wave drag (compressibility drag) is created by the presence of a body moving at high speed through a compressible fluid. In aerodynamics, wave drag consists of multiple components depending on the speed regime of the flight. In transonic flight – at speeds of Mach 0.5 or greater, but still less than Mach 1.0 (aka. speed of sound) – wave drag is the result of local supersonic flow.

Supersonic flow occurs on bodies traveling well below the speed of sound, as the local speed of air on a body increases when it accelerates over the body. In short, aircraft flying at transonic speeds often incur wave drag as a result. This increases as the speed of the aircraft nears the sound barrier of Mach 1.0, before becoming a supersonic object.

In supersonic flight, wave drag is the result of oblique shockwaves formed at the leading and trailing edges of the body. In highly supersonic flows bow waves will form instead. At supersonic speeds, wave drag is commonly separated into two components, supersonic lift-dependent wave drag and supersonic volume-dependent wave drag.

Understanding the role air frictions plays with flight, knowing its mechanics, and knowing the kinds of power needed to overcome it, are all crucial when it comes to aerospace and space exploration. Knowing all this will also be critical when it comes time to explore other planets in our Solar System, and in other star systems altogether!

We have written many articles about air resistance and flight here at Universe Today. Here’s an article on What Is Terminal Velocity?, How Do Planes Fly?, What is the Coefficient of Friction?, and What is the Force of Gravity?

If you’d like more information on NASA’s aircraft programs, check out the Beginner’s Guide to Aerodynamics, and here’s a link to the Drag Equation.

We’ve also recorded many related episodes of Astronomy Cast. Listen here, Episode 102: Gravity.

Posted on by Matt Williams

ESA Regrets Not Buying Windshield Insurance

The chip in the ISS' Cupola window, photographed by astronaut Tim Peake. Credit: ESA/NASA/Tim Peake

It is known as the Cupola, an observation and work area that was installed aboard the International Space Station in 2010. In addition to giving the crew ample visibility to support the control of the Station’s robotic arms, it is also the best seat in the house when it comes to viewing Earth, celestial objects and visiting vehicles. Little wonder then why sp many breathtaking pictures have been taken from inside it over the years.

So you can imagine how frustrating it must be for the crew when a tiny artificial object (aka. space debris) collides with the Cupola’s windows and causes it to chip. And thanks to astronaut Tim Peake and a recent photo he chose to share with the world, people here on Earth are able to see just how this looks from the receiving end for the first time.

Continue reading “ESA Regrets Not Buying Windshield Insurance”

Posted on by Matt Williams

Japanese 3D Galaxy Map Confirms Einstein Was One Smart Dude

An international team of researchers have produced the largest 3-D map of the universe to date, which validates Einstein's theory of General Relativity. Credit: NAOJ/CFHT/ SDSS

On June 30th, 1905, Albert Einstein started a revolution with the publication of theory of Special Relativity. This theory, among other things, stated that the speed of light in a vacuum is the same for all observers, regardless of the source. In 1915, he followed this up with the publication of his theory of General Relativity, which asserted that gravity has a warping effect on space-time. For over a century, these theories have been an essential tool in astrophysics, explaining the behavior of the Universe on the large scale.

However, since the 1990s, astronomers have been aware of the fact that the Universe is expanding at an accelerated rate. In an effort to explain the mechanics behind this, suggestions have ranged from the possible existence of an invisible energy (i.e. Dark Energy) to the possibility that Einstein’s field equations of General Relativity could be breaking down. But thanks to the recent work of an international research team, it is now known that Einstein had it right all along.

Continue reading “Japanese 3D Galaxy Map Confirms Einstein Was One Smart Dude”

Posted on by Matt Williams

Super Secret X-37B Nears One Year In Orbit Doing ???

The X-37B Orbital Test Vehicle taxiing on the flightline on March 30th, 2010, at the Astrotech facility in Titusville, Florida. Credit: USAF

For years now, the program to develop the X-37B spacecraft has been shrouded in secrecy. Originally intended as part of a NASA project to develop a reusable unmanned spacecraft, this Boeing-designed spaceplane was taken over by the Department of Defense in 2004. And while it has been successfully tested on multiple occasions, there remain some unanswered questions as to its intended purpose and what has been taking place during these flights.

This, predictably, has lead to all kinds of rumors and speculation, with some suggesting that it could be a spy plane while others think that it is intended to deliver space-based weapons. It’s latest mission – which was dubbed OTV-4 (Orbital Test Vehicle-4) – has been especially clandestine. And after nearly a year in orbit, it remains unclear what the X37B has been doing up there all this time.

Continue reading “Super Secret X-37B Nears One Year In Orbit Doing ???”

Posted on by Matt Williams

First Hyperloop Technology Demo A Success

After a successful demonstration on their test track, Hyperloop One is one step closer to making Musk's "fifth mode of transportation" a reality. Credit: cbc.ca

Back in 2012, Tesla Motors, Paypal and SpaceX founder Elon Musk made headlines when he announced his idea for a “fifth form of transportation“. Known as the Hyperloop, the concept called for the creation of a high-speed train that would use a low-pressure steel tube and a series of aluminum pod cars to whisk passengers from San Francisco to Los Angeles in just 35 minutes. At the time, Musk claimed he was simply too busy with other projects to build such a system, but that others were free to take a crack at it.

Since then, two startups have emerged that are attempting to do just that. And just yesterday, the startup known as Hyperloop One (formerly Hyperloop Technologies) conducted a test on their full-scale test track located in the Nevada Desert. In what they referred to as a “Propulsion Open Air Test” (POAT), this startup passed a major developmental milestone, bringing them one step closer to making the dream of the Hyperloop a reality.

Using the same linear-accelerator motor that will one day propel podcars through a series of semi-pressurized tubes, the Hyperloop One’s engineers managed to accelerate their test vehicle down a rail track at speeds of up to 483 km/h (300 mph) before plowing it into a sand berm. While this is not quite the 1125 km/h (700 mph) that Hyperloop One hopes to get their pods up to (and there are still matter to work out, such as passenger safety) it is a major step forward.

For one, the test provided some valuable returns that showed that the startup’s eventual goal is realizable. Before it slammed into a pile of sand (on a count of the fact that they have yet to design a braking system) the engineers were able to confirm that the test car had managed to accelerate from 0 to 160 km/h (100 mph) in one second. Within a second and a half, the pod had reached 193 km/h (120 mph), reportedly pulling 2.5 Gs in the process.

Hyperloop's One future test track, which will consist of aluminum tubes under low air pressure. Credit: Hyperloop One
Hyperloop One prototype tube, which is currently under construction in the Nevada Desert. Credit: Hyperloop One

As Josh Giegel, Hyperloop One’s chief engineer, explained in a recent interview with Mashable, the test addressed their system’s linear electric motor-based propulsion. Their design is distinguished from other motors in that it has no moving parts, relying instead on a series of “blades” that measure roughly 60 centimeters long and 15 wide (24 by 6 inches). When powered, these blades create electromagnetic energy that reacts with the pod to propel it along.

Hyperloop One CEO Rob Lloyd was on hand to comment. By 2020, he hopes to sees three lines in operation, with one likely running between San Fransisco and LA and another potentially in Russia. “This was a major technology milestone,” he said. “Hyperloop is faster, greener, safer, and cheaper than any other mode of transportation… We’re building this thing.”

Lloyd also took the occasion to announce new partnerships that the company is entering into – which include architecture, engineering, finance,  freight and tunneling firms – as well as the $80 million in Series B funding they have received. But perhaps the most interesting development to coincide with the test was the decision to change their name. While the reason for this was not explained, the smart money is on it being intended to clear up confusion surrounding the company’s immediate competition.

At present, there are two major companies competing to bring Musk’s vision to life. On the one hand, there is Hyperloop One (formerly Hyperloop Technologies), while the other is Hyperloop Transportation Technologies (or HTT). This little naming scheme has caused quite a bit of confusion in the past, and it is clear at this point that Hyperloop One wants to distinguish itself as being the preeminent leader in the field.

A sled speeds down a track during the test of a Hyperloop One propulsion system Wednesday in North Las Vegas, Nev. Credit: John Locher/The Associated Press)
The test car speeds down the track during the open-air test of the Hyperloop One propulsion system in the Nevada Desert. Credit: John Locher/The Associated Press

But of course, the competition is far from over. In the past few years, HTT has announced some lucrative partnerships as well, which included signing with international engineering giant Aecom and Oerlikon, the world’s oldest vacuum technology company. Earlier this year, HTT also announced an agreement with the Slovakian government to build two Hyperloops that will connect major cities in Central Europe.

One of these lines will run between Vienna, Austria and Bratislava, Slovakia, while the other will connect Bratislava to Budapest, Hungary. The project is expected to cost $200 – $300 million, and is expected to reach an annual capacity of 10 million passengers.

Last, but not least, it is important to note that Hyperloop One’s test comes not long after the Hyperloop Pod Competition, a design competition sponsored by SpaceX that saw 100 university teams compete to create a design for a Hyperloop podcar. The winning team, which hails from MIT, will be testing their final prototype podcar on the one-mile Hyperloop Test Track at SpaceX’s headquarters in California next month.

Much is happening on the Hyperloop front! Who knows where it will all lead? One thing is clear though. Since Musk released the white paper for his concept in 2013 and companies began picking it up, this project has had no shortage of enthusiasts, skeptics and detractors. With every passing milestone, partnership and test, more and more people are beginning to seriously ask, “can it be done?”

Posted on by Matt Williams

Thanks, Comet Pluto. Solar System Nomenclature Needs A Major Rethink

New Horizon's July 2015 flyby of Pluto captured this iconic image of the heart-shaped region called Tombaugh Regio. Credit: NASA/JHUAPL/SwRI.

Pluto can’t seem to catch a break lately. After being reclassified in 2006 by the International Astronomical Union, it seemed that what had been the 9th planet of the Solar System was now relegated to the status of “dwarf planet” with the likes of Ceres, Eris, Haumea, and Makemake. Then came the recent announcements that the title of “Planet 9” may belong to an object ten times the mass of Earth located 700 AU from our Sun.

And now, new research has been produced that indicates that Pluto may need to be reclassified again. Using data provided by the New Horizons mission, researchers have shown that Pluto’s interaction with the Sun’s solar wind is unlike anything observed in the Solar System thus far. As a result, it would seem that the debate over how to classify Pluto, and indeed all astronomical bodies, is not yet over.

Continue reading “Thanks, Comet Pluto. Solar System Nomenclature Needs A Major Rethink”

Posted on by Matt Williams

What Are The Colors of the Planets?

Planets and other objects in our Solar System. Credit: NASA.

When we look at beautiful images of the planets of our Solar System, it is important to note that we are looking at is not always accurate. Especially where their appearances are concerned, these representations can sometimes be altered or enhanced. This is a common practice, where filters or color enhancement is employed in order to make sure that the planets and their features are clear and discernible.

So what exactly do the planets of the Solar System look like when we take all the added tricks away? If we were to take pictures of them from space, minus the color enhancement, image touch-ups, and other methods designed to bring out their details, what would their true colors and appearances be? We already know that Earth resembles something of a blue marble, but what about the other ones?

Continue reading “What Are The Colors of the Planets?”

Posted on by Matt Williams

Will Earth Survive When the Sun Becomes a Red Giant?

Earth scorched by red giant Sun
Artist's impression of the Earth scorched by our Sun as it enters its Red Giant Branch phase. Credit: Wikimedia Commons/Fsgregs

Since the beginning of human history, people have understood that the Sun is a central part of life as we know it. It’s importance to countless mythological and cosmological systems across the globe is a testament to this. But as our understand of it matured, we came to learn that the Sun was here long before us, and will be here long after we’re gone. Having formed roughly 4.6 bullion years ago, our Sun began its life roughly 40 million years before our Earth had formed.

Since then, the Sun has been in what is known as its Main Sequence, where nuclear fusion in its core causes it to emit energy and light, keeping us here on Earth nourished. This will last for another 4.5 – 5.5 billion years, at which point it will deplete its supply of hydrogen and helium and go through some serious changes. Assuming humanity is still alive and calls Earth home at this time, we may want to consider getting out the way!

The Birth of Our Sun:

The predominant theory on how our Sun and Solar System formed is known as Nebular Theory, which states that the Sun and all the planets began billions of years ago as a giant cloud of molecular gas and dust. Then, approximately 4.57 billion years ago, this cloud experienced gravitational collapse at its center, where anything from a passing star to a shock wave caused by a supernova triggered the process that led to our Sun’s birth.

Basically, this took place after pockets of dust and gas began to collect into denser regions. As these regions pulled in more and more matter, conservation of momentum caused them to begin rotating, while increasing pressure caused them to heat up. Most of the material ended up in a ball at the center while the rest of the matter was flattened out into a large disk that circled around it.

Young stars have a disk of gas and dust around them called a protoplanetary disk. Out of this disk planets are formed, and the presence of water ice in the disc affects where different types of planets form. Credit: NASA/JPL-Caltech
Young stars have a disk of gas and dust around them called a protoplanetary disk. Out of this disk planets are formed, and the presence of water ice in the disc affects where different types of planets form. Credit: NASA/JPL-Caltech

The ball at the center would eventually form the Sun, while the disk of material would form the planets. The Sun then spent the next 100,000 years as a collapsing protostar before temperature and pressures in the interior ignited fusion at its core. The Sun started as a T Tauri star – a wildly active star that blasted out an intense solar wind. And just a few million years later, it settled down into its current form.

Main Sequence:

For the past 4.57 billion years (give or take a day or two), the Sun has been in the Main Sequence of its life. This is characterized by the process where hydrogen fuel, under tremendous pressure and temperatures in its core, is converted into helium. In addition to changing the properties of its constituent matter, this process also produces a tremendous amount of energy. All told, every second, 600 million tons of matter are converted into neutrinos, solar radiation, and roughly 4 x 1027 Watts of energy.

Naturally, this process cannot last forever since it is dependent on the presence of matter which is being regularly consumed. As time goes on and more hydrogen is converted into helium, the core will continue to shrink, allowing the outer layers of the Sun to move closer to the center and experience a stronger gravitational force.

This will place more pressure on the core, which is resisted by a resulting increase in the rate at which fusion occurs. Basically, this means that as the Sun continues to expend hydrogen in its core, the fusion process speeds up and the output of the Sun increases. At present, this is leading to a 1% increase in luminosity every 100 million years, and a 30% increase over the course of the last 4.5 billion years.

The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser
The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser

Approximately 1.1 billion years from now, the Sun will be 10% brighter than it is today. This increase in luminosity will also mean an increase in heat energy, one which the Earth’s atmosphere will absorb. This will trigger a runaway greenhouse effect that is similar to what turned Venus into the terrible hothouse it is today.

In 3.5 billion years, the Sun will be 40% brighter than it is right now, which will cause the oceans to boil, the ice caps to permanently melt, and all water vapor in the atmosphere to be lost to space. Under these conditions, life as we know it will be unable to survive anywhere on the surface, and planet Earth will be fully transformed into another hot, dry world, just like Venus.

Red Giant Phase:

In 5.4 billion years from now, the Sun will enter what is known as the Red Giant phase of its evolution. This will begin once all hydrogen is exhausted in the core and the inert helium ash that has built up there becomes unstable and collapses under its own weight. This will cause the core to heat up and get denser, causing the Sun to grow in size.

It is calculated that the expanding Sun will grow large enough to encompass the orbit’s of Mercury, Venus, and maybe even Earth. Even if the Earth were to survive being consumed, its new proximity to the the intense heat of this red sun would scorch our planet and make it completely impossible for life to survive. However, astronomers have noted that as the Sun expands, the orbit of the planet’s is likely to change as well.

When the Sun reaches this late stage in its stellar evolution, it will lose a tremendous amount of mass through powerful stellar winds. Basically, as it grows, it loses mass, causing the planets to spiral outwards. So the question is, will the expanding Sun overtake the planets spiraling outwards, or will Earth (and maybe even Venus) escape its grasp?

K.-P Schroder and Robert Cannon Smith are two researchers who have addressed this very question. In a research paper entitled “Distant Future of the Sun and Earth Revisted” which appeared in the Monthly Notices of the Royal Astronomical Society, they ran the calculations with the most current models of stellar evolution.

According to Schroder and Smith, when the Sun becomes a red giant star in 7.59 billion years, it will start to lose mass quickly. By the time it reaches its largest radius, 256 times its current size, it will be down to only 67% of its current mass. When the Sun does begin to expand, it will do so quickly, sweeping through the inner Solar System in just 5 million years.

It will then enter its relatively brief (130 million year) helium-burning phase, at which point, it will expand past the orbit of Mercury, and then Venus. By the time it approaches the Earth, it will be losing 4.9 x 1020 tonnes of mass every year (8% the mass of the Earth).

But Will Earth Survive?:

Now this is where things become a bit of a “good news/bad news” situation. The bad news, according to Schroder and Smith, is that the Earth will NOT survive the Sun’s expansion. Even though the Earth could expand to an orbit 50% more distant than where it is today (1.5 AUs), it won’t get the chance. The expanding Sun will engulf the Earth just before it reaches the tip of the red giant phase, and the Sun would still have another 0.25 AU and 500,000 years to grow.

Red giant. Credit:NASA/ Walt Feimer
Artist’s impression of a Red giant star. Credit:NASA/ Walt Feimer

Once inside the Sun’s atmosphere, the Earth will collide with particles of gas. Its orbit will decay, and it will spiral inward. If the Earth were just a little further from the Sun right now, at 1.15 AU, it would be able to survive the expansion phase. If we could push our planet out to this distance, we’d also be in business. However, such talk is entirely speculative and in the realm of science fiction at the moment.

And now for the good news. Long before our Sun enters it’s Red Giant phase, its habitable zone (as we know it) will be gone. Astronomers estimate that this zone will expand past the Earth’s orbit in about a billion years. The heating Sun will evaporate the Earth’s oceans away, and then solar radiation will blast away the hydrogen from the water. The Earth will never have oceans again, and it will eventually become molten.

Yeah, that’s the good news… sort of. But the upside to this is that we can say with confidence that humanity will be compelled to leave the nest long before it is engulfed by the Sun. And given the fact that we are dealing with timelines that are far beyond anything we can truly deal with, we can’t even be sure that some other cataclysmic event won’t claim us sooner, or that we wont have moved far past our current evolutionary phase.

An interesting side benefit will be how the changing boundaries of our Sun’s habitable zone will change the Solar System as well. While Earth, at a mere 1.5 AUs, will no longer be within the Sun’s habitable zone, much of the outer Solar System will be. This new habitable zone will stretch from 49.4 AU to 71.4 AU – well into the Kuiper Belt – which means the formerly icy worlds will melt, and liquid water will be present beyond the orbit of Pluto.

Perhaps Eris will be our new homeworld, the dwarf planet of Pluto will be the new Venus, and Haumeau, Makemake, and the rest will be the outer “Solar System”. But what is perhaps most fascinating about all of this is how humans are even tempted to ask “will it still be here in the future” in the first place, especially when that future is billions of years from now.

Somehow, the subjects of what came before us, and what will be here when we’re gone, continue to fascinate us. And when dealing with things like our Sun, the Earth, and the known Universe, it becomes downright necessary. Our existence thus far has been a flash in the pan compared to the cosmos, and how long we will endure remains an open question.

We have written many interesting articles on the Sun here at Universe Today. Here’s What Color Is The Sun?, What Kind of Star is the Sun?, How Does The Sun Produce Energy?, and Could We Terraform the Sun?

Astronomy Cast also has some interesting episodes on the subject. Check them out- Episode 30: The Sun, Spots and All,  Episode 108: The Life of the Sun, Episode 238: Solar Activity.

For more information, check out NASA’s Solar System Guide.