Posted on by Tega Jessa

First Rocket

Dr. Robert Goddar with on his early rockets in Roswell

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Rocketry is actually older than many people think. The first rockets originated in China and subsequently the Middle East with the discovery of gunpowder. These rockets were used for military purposes or as entertainment. The use of rockets and gunpowder would eventually transform warfare, and to this day we still use rockets in pretty much the same way they were used 700 years ago. The only difference is that when we use rockets for military purposes we call them missiles and when used for entertainment they can be toys or pyrotechnics.

The composition of the first rocket was what is now in aeronautics called a solid rocket. This rocket runs on a solid fuel that burned inside the rocket. The heated exhaust is expelled out the bottom the rocket, creating the thrust needed to fly. The composition of solid fuel rockets is still pretty much the same as in ancient times.

The casing is the body of the rocket. Rockets were made differently depending upon their end use. For example, solid rockets that were used in space programs had steel casings. The next important element of a solid rocket was the grain. The grain is the solid fuel needed to power the missile. The first types used had gunpowder as the grain but the formula could be altered. If you ever saw a fireworks display, this is why the explosions have different colors. The additions of different metals and composites in the grain of the rockets creates this effect. The final components; the fuse. This was the ignition device used to start the combustion process of the rockets fuel. Later as rocketry was further researched a nozzle was added to the design to better direct exhaust and improve thrust.

The first rockets that were used in modern rocketry was invented by Dr. Robert Goddard. For this he is known as the Father of Modern Rocketry. He created the first successful liquid fuel rocket, adding the nozzle design that is so common today. The liquid fuel rocket ran on a slightly different design than its predecessor with the fuel being released from a pressure tank to a combustion chamber where it was mixed with air or another oxidizer to burn and create heated exhaust which was directed away to create thrust. This would be the design that would pave the way for modern aeronautics and eventually space exploration.

So as we see rockets have come a long way from their earliest day. Nevertheless, they are still playing an important role in the development of human technology. Making new advances possible every day with the missions and experiments they support.

If you enjoyed this article there are other related articles on the Universe Today website you might want to checkout. Here is an article that talks more about solid fuel rockets. If you want to learn more about modern rockets this article on new advances made on liquid fuel rockets.

There are other interesting articles you can find on the web. Time magazine has a great profile article on Robert Goddard. Another good resource is the NASA website which has a brief article on the history of rockets.

You might also enjoy listening to an episode of Astronomy Cast. Episode 100 Rockets is relevant to the stuff talked about in the article.

Source: Wikipedia

Posted on by John Carl Villanueva

What is the Gravitational Constant?

Visualization of a massive body generating gravitational waves (UWM)

The gravitational constant is the proportionality constant used in Newton’s Law of Universal Gravitation, and is commonly denoted by G. This is different from g, which denotes the acceleration due to gravity. In most texts, we see it expressed as:

G = 6.673×10-11 N m2 kg-2

It is typically used in the equation:

F = (G x m1 x m2) / r2 , wherein

F = force of gravity

G = gravitational constant

m1 = mass of the first object (lets assume it’s of the massive one)

m2 = mass of the second object (lets assume it’s of the smaller one)

r = the separation between the two masses

As with all constants in Physics, the gravitational constant is an empirical value. That is to say, it is proven through a series of experiments and subsequent observations.

Although the gravitational constant was first introduced by Isaac Newton as part of his popular publication in 1687, the Philosophiae Naturalis Principia Mathematica, it was not until 1798 that the constant was observed in an actual experiment. Don’t be surprised. It’s mostly like this in physics. The mathematical predictions normally precede the experimental proofs.

Anyway, the first person who successfully measured it was the English physicist, Henry Cavendish, who measured the very tiny force between two lead masses by using a very sensitive torsion balance. It should be noted that, after Cavendish, although there have been more accurate measurements, the improvements on the values (i.e., being able to obtain values closer to Newton’s G) have not been really substantial.

Looking at the value of G, we see that when we multiply it with the other quantities, it results in a rather small force. Let’s expand that value to give you a better idea on how small it really is: 0.00000000006673 N m2 kg-2

Alright, let’s now see what force would two 1-kg objects exert on one another when their geometrical centers are spaced 1 meter apart. So, how much do we get?

F = 0.00000000006673 N. It really doesn’t matter much if we increase both masses substantially.

For example, let’s try the heaviest recorded mass of an elephant, 12,000 kg. Assuming we have two of these, spaced 1 meter apart from their centers. I know it’s difficult to imagine that since elephants are rather stout, but let’s just proceed this way because I want to put emphasis on the significance of G.

So, how much did we get? Even if we rounded that off, we’d still obtain only 0.01 N. For comparison, the force exerted by the earth on an apple is roughly 1 N. No wonder we don’t feel any force of attraction when we sit beside someone… unless of course you’re a male and that person is Megan Fox (still, it’d be safe to assume that the attraction would only be one way).

Therefore, the force of gravity is only noticeable when we consider at least one mass to be very massive, e.g. a planet’s.

Allow me to end this discussion with one more mathematical exercise. Assuming you know both your mass and your weight, and you know the radius of the earth. Plug those into the equation above and solve for the other mass. Voila! Wonder of wonders, you’ve just obtained the mass of the Earth.

You can read more about the gravitational constant here in Universe Today. Want to learn more about a new study that finds fundamental force hasn’t changed over time? There’s also some insights you can find among the comments in this article: Record Breaking “Dark Matter Web” Structures Observed Spanning 270 Million Light Years Across

There’s more about it at NASA. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:

Posted on by John Carl Villanueva

What is Entropy?

After some time, this cold glass will reach thermal equilibrium

Perhaps there’s no better way to understand entropy than to grasp the second law of thermodynamics, and vice versa. This law states that the entropy of an isolated system that is not in equilibrium will increase as time progresses until equilibrium is finally achieved.

Let’s try to elaborate a little on this equilibrium thing. Note that in the succeeding examples, we’ll assume that they’re both isolated systems.

First example. Imagine putting a hot body and a cold body side by side. What happens after some time? That’s right. They both end up in the same temperature; one that is lower than the original temperature of the hotter one and higher than the original temperature of the colder one.

Second example. Ever heard of a low pressure area? It’s what weather reporters call a particular region that’s characterized by strong winds and perhaps some rain. This happens because all fluids flow from a region of high pressure to a region of low pressure. Thus, when the fluid, air in this case, comes rushing in, they do so in the form of strong winds. This goes on until the pressures in the adjacent regions even out.

In both cases, the physical quantities which started to be uneven between the two bodies/regions even out in the end, i.e., when equilibrium is achieved. The measurement of the extent of this evening-out process is called entropy.

During the process of attaining equilibrium, it is possible to tap into the system to perform work, as in a heat engine. Notice, however, that work can only be done for as long as there is a difference in temperature. Without it, like when maximum entropy has already been achieved, there is no way that work can be performed.

Since the concept of entropy applies to all isolated systems, it has been studied not only in physics but also in information theory, mathematics, as well as other branches of science and applied science.

Because the accepted view of the universe is that of one that is finite, then it can very well be considered as a closed system. As such, it should also be governed by the second law of thermodynamics. Thus, like in all isolated systems, the entropy of the universe is expected to be increasing.

So what? Well, also just like all isolated systems, the universe is therefore also expected to end up in a useless heap in equilibrium, a.k.a. a heat death, wherein energy can no longer be extracted from anymore. To give you some relief, not everyone involved in the study of cosmology is totally in agreement with entropy’s so-called role in the grand scheme of things though.

You can read more about entropy here in Universe Today. Want to know why time might flow in one direction? Have you ever thought about the time before the Big Bang? The entire entropy concept plays an important role in understanding them.

There’s more about entropy at NASA and Physics World too. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Source:
Hyperphysics

Posted on by John Carl Villanueva

Acceleration Due to Gravity

Low gravity on an asteroid would be a big issue (NASA)

[/caption]The acceleration due to gravity is the acceleration of a body due to the influence of the pull of gravity alone, usually denoted by ‘g’. This value varies from one celestial body to another. For example, the acceleration due to gravity would be different on the Moon as compared to the one here on Earth. Similarly, you would have different values for both Jupiter and Pluto.

Since acceleration is a vector quantity, it must possess both a magnitude and a direction. The values we were referring to earlier pertained to the magnitude. As for the direction, in all instances, it should be directed to the center of the celestial body. Now, since these celestial bodies are rather large relative to the size of the observer, in this case being you and I, the direction is taken as downward.

Direction of g

Why downward? Well, as stated earlier, g is the acceleration of a body if we consider only the pulling force of the gravitational field. Now, since the acceleration of a body always takes the direction of the net force acting on that body, and since the only force we are considering is that of gravity, then this acceleration should take the direction of gravity, i.e., downward.

Don’t worry. The direction of g is mostly important only in the mathematical solutions of physics problems. What you should be more concerned with is the magnitude of g. Although this magnitude varies from one celestial body to another, you might want to know what the value of g is here on Earth.

Magnitude of g

The average value of g on the surface of the Earth is around 9.8 m/s2. Average? So there are other possible values? That’s right. The value of g becomes larger as the object gets nearer to the Earth’s core. So, you’d have a slightly larger g at sea level compared to what you’d have at the peak of say, the Himalayas.

Furthermore, since the Earth is not a perfect sphere but, rather, an oblate spheroid, i.e., bulging at the equator and flat at the poles, then you would have greater g’s at the poles than at the equator.

To end, let me just elaborate more on what we mean by 9.8 m/s2 as some people confuse this with speed. When we say that an object falling freely (under the influence of gravity alone) accelerates at 9.8 m/s2, we simply mean that its speed is increasing by 9.8 m/s every second. Hence, after 1 second of falling, its speed would be 9.8 m/s. After another 2 seconds of falling, it would then be 19.6 m/s and so on.

We have some related articles here that may interest you:

There’s more about it at NASA. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:
Decelerating Black Holes, Earth-Sun Tidal Lock, and the Crushing Gravity of Dark Matter
Gravity

Sources:
Wikipedia
The Physics Classroom
Haverford College

Posted on by John Carl Villanueva

Visible Light

Sunlight passing through a prism. Image credit: NASA

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Of all the wavelengths in the electromagnetic spectrum, those that lie between 400 nm to 700 nm are the ones most familiar to us. That’s because these are the waves that comprise what we call visible light. 

When we see objects, it’s because they’re being illuminated by visible light. When we see that the sky is blue, or the grass is green, or hair black, or that an apple is red, that’s because we’re seeing different wavelengths within the 400nm-700nm band. Because of the waves in this band, a lot has been learned about the properties of electromagnetic waves.

Through visible light, reflection & refraction are easily observed. So are interference and diffraction. Mirrors, lenses, prisms, diffraction gratings, and spectrometers have all been put to use to understand and manifest the qualities of the light that we see through our naked eyes.

Galileo’s telescope, which was composed of a simple set of lenses, made use of the refractive properties of light to magnify distant objects. Today’s  binoculars and periscopes capitalize on the optical phenomenon called Total Internal Reflection by using prisms to improve on what early refractive telescopes were capable of achieving.

As mentioned earlier, visible light is made up of the wavelengths that range from 400 nm to 700 nm. Each wavelength is characterized by a unique color, with violet on one end (adjacent to ultraviolet light) and red on the other (adjacent to infrared light). When all these wavelengths are combined together, they make up what is known as white light. 

You can separate these wavelengths (and the corresponding colors) by letting them pass through either a prism or a diffraction grating. The magnificent array of colors that we see in a rainbow, on a diamond, or even a peacock’s tail are examples of this separation.

All phenomena of visible light such as reflection, refraction, interference, and diffraction are also exhibited by non-visible wavelengths. Hence, by understanding these phenomena, and applying them to the non-visible wavelengths, scientists were able to unearth many of nature’s secrets. In fact, if we trace back the roots of modern physics, particularly the wave-particle duality of matter, we will be led back to its manifestation in visible light. 

The study of visible light falls under the realm of optics. Among the scientists who have contributed substantially to the development of optics are Christiaan Huygens for his wavelets and a wave theory of light, Isaac Newton for his contributions on reflection and refraction, James Clerk Maxwell for the propagation of electromagnetic waves as explained in a series of equations, and Heinrich Hertz for verifying the truth of those equations through experiments.

You can read more about visible light here in Universe Today. Want to know where visible light comes from? How about a visible light image of a distant galaxy?

There’s more about it at NASA and Physics World:
Visible Light Waves
The special effect of physics

Here are two episodes at Astronomy Cast that you might want to check out as well:
Optical Astronomy
Interferometry

Sources:
Windows to Universe
NASA: Visible Light
Wikipedia: Christiaan Huygens
NASA: Maxwell and Hertz

Posted on by Abby Cessna

Plane of the Ecliptic

Solar eclipse. Credit: NASA

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Plane of the ecliptic, also known as the ecliptic plane, is a phrase you will often hear in astronomy. A basic definition is that the plane of the ecliptic is the plane of the Earth’s orbit, but that does not mean much to most people. Space is a three-dimensional vacuum, which you can think of as a kind of pool with the planets suspended in it. The Earth orbits the Sun on a particular angle and its orbit is elliptical in shape. The orbit is often shown as an ellipse made of dotted lines with the Sun at its center. If you made this ellipse a solid surface and extended it infinitively, then you would have the plane of the ecliptic. Actually our entire Solar System can be thought of as flat because all of the planets’ orbits are near or on this plane.

The ecliptic plane is used as the main reference when describing the position of other celestial objects in our Solar System. The angle between the plane of the ecliptic and the plane of an orbit is called the inclination. Until it was stripped of its status as a planet, Pluto was the planet with the most extreme inclination – 17°. Mercury is the only other planet with a significant inclination of 7°. There is also a 7° inclination between the plane of the Sun’s equator and the ecliptic plane. There are other celestial bodies that have a much greater inclination than any of the planets, such as Eris with a 44° inclination or Pallas with a 34° inclination.

The ecliptic plane got its name from the fact that a solar eclipse can only happen when the Moon crosses this plane to block out the Sun. Our Moon crosses the ecliptic about twice a month. A solar eclipse occurs when a new Moon crosses the ecliptic, and a lunar eclipse occurs when a full Moon crosses it.

Seasons on Earth are caused by our planet’s axial tilt of 23.5°, which causes variations in the amount of sunlight different parts of the Earth receive. This goes for all the other planets too. For example, Uranus rotates on its side with an axial tilt of 97.8°, which results in extreme variations in its seasons. The eclipse is also home to the constellations of the zodiac. There are twelve constellations in the zodiac, which are important symbols in astrology and can also be found in the Chinese calendar.  Here’s a list of all the zodiac symbols.

Universe Today has a number of articles including Virgo one of the zodiac signs and axial tilt.

You should also check out these articles on the ecliptic plane and ecliptic facts for more information.

Do not forget to tune into Astronomy Cast’s episode about the planet’s orbits.

Reference:
NASA: The Path of the Sun, the Ecliptic

Posted on by Abby Cessna

Minor Planets

Main Belt Asteroids
Ceres, the recently promoted dwarf planet in the asteroid belt is still too small to be easily seen by Hubble credit: NASA/ESA/STScI

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Minor planet is a term used to refer to a celestial object – that is not a planet or comet – which orbits the Sun. Found in 1801, Ceres, also known as a dwarf planet, was the first minor planet discovered. The term minor planet has been in use since the 1800’s. Planetoids, asteroids, and minor planets have all been used interchangeably, but the situation became even more confusing when the International Astronomical Union (IAU) committee reclassified minor planets and comets into the new categories of dwarf planets and small solar system bodies. At the same time, the IAU created a new definition of what a planet is, and Pluto was reclassified as a dwarf planet. Hydrostatic equilibrium – the ability to maintain a roughly spherical shape – is what separates dwarf planets from the more irregularly shaped small solar system bodies. The names become even more confusing because the IAU still recognizes the use of the term minor planets.

Minor planets are extremely common with over 400,000 registered and thousands more found each month. Approximately 15,000 minor planets have been given official names while the rest are numbered. When asteroids were first discovered, they were named after characters from Greek and Roman mythology like Ceres was. At first, astronomers thought that the asteroids, especially Ceres and Pallas were actually planets. Astronomers also created symbols for the first asteroids found. There were symbols created for 14 asteroids and some of them were very complex like Victoria’s symbol, which looks like a plant with three leaves growing out of an off center starburst. Soon, astronomers ran out of mythological names and started christening asteroids after television characters, famous people, and relatives of discoverers. Most names were feminine, attesting to an unnamed  tradition. As the numbers ran into the thousands, scientists started using their pets as inspiration. After an asteroid was named 2309 Mr. Spock, pet’s names were banned. That did not stop the oddness though because names such as 9007 James Bond and 6402 Chesirecat have been suggested and actually accepted.

There are a number of different categories that minor planets fall into including asteroids, Trans-Neptunian objects, and centaurs. There  are various types of asteroids, although most of them can be found in the asteroid belt, which is the region of space between Mars and Jupiter. Trans-Neptunian objects are celestial bodies found orbiting beyond Neptune, and centaurs are celestial bodies with unstable orbits located between Jupiter and Neptune. The categories also overlap, making classifying things a nightmare. For example, Ceres is a dwarf planet and minor planet, additionally it can also be classified as an asteroid.

Universe Today has a number of articles including astronomers find new minor planet and why Pluto is no lone a planet.

You can also check out these articles on asteroids and the solar system.

Astronomy Cast has an episode on the asteroid belt you will want to listen to.

Reference:
Wikipedia

Posted on by Abby Cessna

Habitable Planet

Habitable zone

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The term “habitable planet” seems rather broad. Does it mean that it is habitable for humans? Is it merely capable of supporting some other form of life? Quite simply, planetary habitability refers to a planet’s ability to both develop and sustain life.

Unfortunately, scientists have had to base their calculations for a habitable planet on Earth’s characteristics and do some guesswork. Some of the factors that astronomers look at when evaluating a planet’s habitability are mass, surface characteristics, orbit, rotation, and geochemistry.

One of the most basic assumptions that astronomers make when searching for a habitable planet is that it has to be terrestrial. This means that the planet is composed mostly of rock and metal and has a solid surface. A gas giant on the other hand has no solid surface, which makes it an unlikely candidate for supporting life. Mass is also an important factor, because low mass planets have too little gravity to keep their atmosphere. They also do not have live volcanoes and other geologic activity, which helps temper the surface to support life, because they lose energy as a result of a small diameter. Planets with high orbital eccentricity – the irregularity of the orbit – have a greater fluctuation in surface temperatures because they are closer to the Sun at some points and much further away at other points in the orbit. In order to be habitable, a planet has to have a moderate rotation. If there is no axial tilt then there are no change of seasons, and if the axial tilt is too severe than the planet will have a difficult time achieving homeostasis – balance. Another assumption astronomers make when determining planetary habitability is that life on other planets will also be carbon-based. The four elements most important for life are oxygen, nitrogen, carbon, and hydrogen. With so many considerations, it is not surprising that scientists have a difficult time determining whether a planet can sustain life.

Astronomers are searching for habitable planets in other solar systems too. They have started by searching in the habitable zones of other solar systems. A habitable zone is the region in space with conditions most favorable for supporting life. Astronomers are unsure exactly what the extent of the habitable zone of our Solar System is. Earth is located in the center of it, but it may even extend as far as Mars, and it almost reaches Venus. The habitable zone and planetary habitability focus on carbon-based life, so they do not help predict other forms of life.

Universe Today has a number of articles you should take a look at including the habitable zone and number of habitable planets.

You should also check out habitable planets and habitable planets are common.

Astronomy Cast has an episode on the search for water on Mars, which tells why finding water is a clue to finding life.

Posted on by Fraser Cain

Have Humans Visited Mercury?

The MESSENGER spacecraft at Mercury (NASA)

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Have astronauts from Earth ever stepped foot on Mercury? No, Mercury has been visited by spacecraft from Earth, but no human has ever gone into orbit around Mercury, let alone stepped on the surface. Just what would it take to visit Mercury?

Humans attempting to visit Mercury would find a similar environment to the Moon. Mercury is airless, so they would need a spacesuit to protect themselves from the vacuum of space. However, the temperatures on Mercury are much greater. During the daytime, the surface of Mercury at the equator rises to 700 Kelvin (427 degrees C). Just for comparison, the surface of the Moon only rises to 390 Kelvin (117 degrees C) during the daytime. So you would need some kind of protection from the intense heat.

But then, nighttime on Mercury dips down to only 100 Kelvin (-173 degrees C) – that’s the same low temperatures you get on the Moon at night. So an astronaut’s spacesuit would need to be able to keep an astronaut warm when they’re in the shade.

The travel time to the Moon is only about 3 days. But the travel time to Mercury is much longer. That’s partly because Mercury is much further away – 10s of millions km. But spacecraft also need to take special trajectories so they can get into orbit around Mercury. All of the spacecraft that have visited Mercury have taken longer than a year to reach the planet. That would be a long, hot journey for astronauts.

Maybe some day in the future humans will visit Mercury, but it hasn’t happened yet.

We have written many stories about Mercury here on Universe Today. Here’s an article about a the discovery that Mercury’s core is liquid. And how Mercury is actually less like the Moon than previously believed.

Want more information on Mercury? Here’s a link to NASA’s MESSENGER Misson Page, and here’s NASA’s Solar System Exploration Guide to Mercury.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Reference:
NASA Star Child: Mercury

Posted on by Fraser Cain

Geology of Mercury

Caloris Basin on Mercury

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The geology of Mercury is similar to the geology of the Moon; although, Mercury is a much denser planet with a larger liquid iron core. But when you look at photographs of Mercury, it really looks like you’re looking at the Moon. The surface of Mercury is covered by impact craters and lava plains.

Planetary scientists can judge the age of a planet’s surface by the number and size of impact craters. In the case of Mercury, there are enough craters that scientists think that the surface of Mercury is largely unchanged for billions of years. It’s believed that the surface of Mercury is geologically inactive; although, only 55% of the surface has been mapped in enough detail to see its geology.

Mercury formed with the rest of the Solar System about 4.6 billion years ago. After that was a period of heavy bombardment by asteroids and comets; this lasted until 3.8 billion years ago. All of the planets in the Solar System were beaten up during the Late Heavy Bombardment period, but we can still see the scars on Mercury and the Moon. Some of the largest craters in this period were filled with lava from Mercury’s interior. It’s believed that vulcanism on Mercury ended during its first 700 800 million years.

Craters on Mercury can be small bowl-shaped pockets, or huge impact craters hundreds of kilometers across. The largest crater on Mercury is the Caloris Basin, measuring 1,550 km across. There have been about 15 large impact basins identified on Mercury. Just like the Moon, the larger craters have bright rays of material; it’s brighter because it hasn’t been as weathered by impacts.

One of the unique places on Mercury are the regions around its poles. Astronomers using radar telescopes have detected large deposits of water ice around Mercury’s poles. It’s believed these deposits of ice are located in deep craters near Mercury’s poles where they’re always in shadow. It’s possible these were deposited by comet impacts billions of years ago.

We have written many stories about Mercury here on Universe Today. Here’s an article about a the discovery that Mercury’s core is liquid. And how Mercury is actually less like the Moon than previously believed.

Want more information on Mercury? Here’s a link to NASA’s MESSENGER Misson Page, and here’s NASA’s Solar System Exploration Guide to Mercury.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

References:
NASA Solar System Exploration: Mercury
NASA: The Solar System’s Big Bang