Guide to Space Archives

May 27, 2010December 24, 2015 by Fraser Cain

How Many Miles to the Center of the Earth?

[/caption]
Were you wondering how many miles to the center of the Earth? The simple quick answer is 3,958.8 miles – the mean radius of the Earth in miles. In other words, if you dug a tunnel straight down, you’d reach the center of the Earth after going 3,958.8 miles, and then you’d need to go another 3,958.8 miles to reach the opposite side of the planet.

But wait, if you need to be really precise, the answer depends on where you’re standing on Earth. That’s because the Earth isn’t a perfect sphere. It’s rotating in space, and so it bulges around the middle, while it’s more flattened at the poles. And so, if you’re standing at the poles, you’re only 3,949.9 miles from the center of the Earth. And if you’re standing on the equator, the distance is 3,963.2 miles.

The difference between those two amounts is 13.3 miles. In other words, you would have to dig 13.3 miles further if you were standing on the equator to reach the center of the planet.

This might not sound like much, but it’s actually a pretty big deal. The furthest point from the center of the Earth isn’t Mount Everest. In fact, it’s Mount Chimborazo in Ecuador. Even though it’s shorter than Mount Everest, it’s actually 8,969.8 feet further from the center of the Earth because it’s located near the equator.

We’ve written several articles about the center of the Earth for Universe Today. Here are some interesting facts about the Earth, and here’s an article about the radius of the Earth.

Want to learn more about the interior of the Earth? Check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We have also recorded an episode of Astronomy Cast all about the Earth. Listen here, Episode 51: Earth.

April 8, 2010December 24, 2015 by John Carl Villanueva

Surface of the Moon

[/caption]Despite the close proximity between the Earth and the Moon, there’s a big difference between the surface of the Moon and of Earth’s. Much of the difference between the two celestial bodies is caused by the absence of the following attributes on the Moon: an atmosphere, bodies of water, and plate tectonics.

Since the Earth’s Moon doesn’t have a significant atmosphere, nothing can stop even the smallest meteoroids from striking its surface. As a result, the lunar surface is heavily cratered. As a matter of fact, tiny craters are quite common even on lunar rocks. This was observed on the Moon rocks brought home by the Apollo missions.

By contrast, small meteoroids that pass through the Earth’s atmosphere are easily vaporized and hence are not able to form craters on the land below.

The absence of liquid water on its surface has allowed the Moon to preserve much of its ancient geological features. Here on Earth, erosion can alter and cover formations over time. Plate tectonics, which is also absent on the Moon, is another big factor that makes the terrain of the two celestial bodies different.

Here on Earth, plate tectonics cause volcanic activities, earthquakes, and sea floor spreading.

Due to the lack of water and atmosphere, the lunar regolith (also called “lunar soil”) is noticeably dry and devoid of air. It also does not contain anything organic. The regolith comes from meteor impacts that has plagued the Moon since its inception.

Impact crater sizes on the lunar surface range from the tiny holes that mark lunar rocks to the really big ones like the South Pole Aitken Basin that has a diameter of approximately 2,500 km. Younger craters are superimposed over older ones. This characteristic is used by scientists to determine the relative ages of impact craters.

Basically, it has been observed that the size of impact craters on the surface of the Moon have decreased over time.

Other prominent geological features found on the surface of the Moon include maria, rilles, domes, wrinkle ridges, and grabens.

The maria, which comprise about one-third of the Moon’s near side, are made up of flows of basaltic lava formed from volcanic activities that occurred in the younger years of the Moon. They were once mistaken for seas on the surface of the Moon, hence the name. Maria is the Latin word for seas. The near side refers to the side of the Moon that is constantly facing Earth.

Here’s a list of popular craters on Earth from Universe Today.

Come October 9, 2009, LCROSS will perform a lunar impact. Find out which crater NASA has chosen for the impact. If you want to know more about the largest crater on the Moon, NASA’s got the right stuff.
There are some interesting episodes from Astronomy Cast that we’d like to recommend:
The Source of Atmospheres, the Vanishing Moon, and a Glow After Sunset
The Moon, Part 1

References:
http://www.nasa.gov/mission_pages/LRO/multimedia/lro-20100709-basin.html
http://curator.jsc.nasa.gov/lunar/letss/Regolith.pdf

April 6, 2010December 24, 2015 by John Carl Villanueva

What is a Joule?

When we raise an apple up to a height of one meter, we perform approximately one joule of work. So what is a joule?

Joule is the unit of energy used by the International Standard of Units (SI). It is defined as the amount of work done on a body by a one Newton force that moves the body over a distance of one meter. Wait a minute … is it a unit of energy or a unit of work?

Actually, it is a unit of both because the two are interrelated. Energy is just the ability of a body to do work. Conversely, work done on a body changes the energy of the body. Let’s go back to the apple example mentioned earlier to elaborate.

An apple is a favorite example to illustrate a one joule of work when using the definition given earlier (i.e., the amount of work done ….) because an apple weighs approximately one Newton. Thus, you’d have to exert a one Newton upward force to counteract its one Newton weight. Once you’ve lifted it up to a height of one meter, you would have performed one joule of work on it.

Now, how does energy fit into the picture? As you perform work on the apple, the energy of the apple (in this case, its potential energy) changes. At the top, the apple would have gained about one joule of potential energy.

Also, when the apple is one meter above its original position, say the floor, gravity would have gained the ability to do work on it. This ability, when measured in joules, is equivalent to one joule.

Meaning, when you release the apple, the force of gravity, which is simply just the weight of the body and equivalent to one Newton, would be able to perform one joule of work on it when the apple drops down from a height of one meter.

Mathematically, 1 joule = 1 Newton ⋅ meter. However, writing it as Newton ⋅ meter is discouraged since it can be easily confused with the unit of torque.

Particle physics experiments deal with large amounts of energies. That is why it is also known as high energy physics. If you liked our answer to the question, “What is a Joule?”, you might want to read the following articles from Universe Today:

Rare Binary Pulsars Provide High Energy Physics Lab
New Particle Throws Monkeywrench in Particle Physics
Physics World also has some more:
Particle physics: the next generation
To the LHC and beyond
Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:
The Large Hadron Collider and the Search for the Higgs-Boson
Antimatter

Sources:
University of Wisconsin
Wikipedia
University of Virginia

April 6, 2010October 31, 2016 by Tega Jessa

How Many Oceans are there in the World?

How many oceans are there in the world? This question may not be as easy to answer as you may think. First we need to see the origins of the word ocean. The Ancient Greeks gave us the word ocean and it described what was to them the outer sea that surrounded the known world. Even then the ancients later believed that there were only 7 seas, the Mediterranean, the Caspian, the Adriatic, the Red Sea, the Black Sea, the Persian Gulf and the Indian Ocean.

The number of oceans in the world varies on how you look at it. From the scientific point of view there is only one major ocean called the World Ocean and if you include inland seas such as the Black Sea and Caspian Sea there are 3. The scientific method of counting oceans looks at saline bodies of water that have oceanic crust.

Another way to look at it is to divide the world ocean by the different continents and other major geographic regions it touches. Using this method there are 5 oceans. There is the Atlantic Ocean which separates the American Continents from Europe and Africa. Then there is the Pacific which separates Asia and the Americas. The Southern Ocean is tricky but is named as such because it encircles Antarctica touches Australia and the southern end of South America. The Indian Ocean is named after Indian subcontinent. The Arctic Ocean is named for its location north of all the continents and being the North Pole. Originally only the Southern Ocean was not officially recognized so this only demonstrates how the designation can easily change.

The way you count the oceans can vary depending on your profession or understanding of the Ocean. Either way you look at the large bodies of salt water are very important. They are a major source of food, regulate the Earth’s climate and are the major source water for all life.

So in the end it becomes not so important to know how many oceans there are but what the ocean is and how important it is to life on this planet.

If you enjoyed this article there are several other articles on Universe Today that you will like and find interesting. There is a great article on sea floor spreading and another interesting piece on ancient oceans.

You can also find some great resources on oceans online. You can learn more about oceans currents and how they affect climate. You can also learn about Ocean Biomes on University of Richmond website.

You should also check out Astronomy Cast. Episode 143 talks about astrobiology.

Sources:
World Atlas
NOAA
Wikipedia

March 30, 2010December 24, 2015 by John Carl Villanueva

What Is Static Electricity?

[/caption]Wonder why you sometimes get zapped when touching a doorknob especially during winter? People will tell you it’s a simple case of static electricity. But what is static electricity?

In some texts, static electricity is a term supposedly used for electricity that does not deal with moving charges. Actually, there is movement of charges. In fact, when you get zapped, charges are actually moving between your fingers and the doorknob. However, the movement is only brief compared to the current in a closed circuit.

So how do stationary charges allow people to get zapped? To understand this phenomenon, try to recall the particles that make up an atom. That’s right, the protons, neutrons, and electrons.

Of the three, electrons are easily removed from an atom since the forces that bind them to an atom are weaker than those that hold the neutrons and protons together in the atoms’ nuclei.

Now, there are some materials that easily lose their electrons compared to others. We’ve included a list below ranking some materials based on their ability to lose electrons. The one at the top has a greater tendency to lose electrons while the one at the bottom has the least.

human hands
glass
nylon
fur
silk
aluminum
steel
hard rubber
vinyl(PVC)
Teflon

Such a list is known as a triboelectric series. A true triboelectric series would have positives and negatives but we won’t go into that here.

Therefore, based on the list, if you rubbed a glass rod with a silk cloth, it is the glass rod that would lose electrons to the cloth. When this happens, the glass rod becomes positively charged, while the silk cloth (having gained excess electrons) becomes negatively charged.

Then when you draw the glass rod close to small bits of paper, the positively charged glass rod repels the electrons in the paper (pushing them to one side in the paper) and attracting the positive side. This allows the bits of paper to stick to the glass rod.

In the case of people getting zapped, they usually gain electrons when they walk across a carpeted floor. The interaction is between the carpet and the soles of their shoes but the overall charge of their bodies get affected. You can imagine them as walking negatively-charged bodies.

So, when they touch a metal door knob, the excess electrons readily leap from their hands to the metal knob and they get zapped.

Actually, static electricity is a rather lengthy physics topic that covers more than just the zapping phenomena. It includes discussions on induction, conduction, Coulomb’s Law, and electric fields, to mention a few. However, when a regular person asks, “what is static electricity?”, he most likely wants you to explain about the painful sensation he experiences upon touching a door knob.

Coulomb’s Law deals with charges. Universe Today has articles talking about the charge of the proton and the charge of the electron.

NASA also has some related stuff. Check out the following articles:
Charges
Killer Electrons

Here are two episodes at Astronomy Cast that you might want to check out as well:
Antimatter
The Search for Dark Matter

Sources:
Wikipedia
How Stuff Works
The Physics Classroom

March 30, 2010December 24, 2015 by John Carl Villanueva

What Is Sound?

[/caption]Light and sound are both waves. However, the former can travel through a vacuum while the latter cannot. So what is sound and how does it propagate as a wave?

Sound is actually a pressure wave. When an object vibrates, it creates a mechanical disturbance in the medium in which it is directly adjacent to. Usually, the medium is air. The medium then carries the disturbance in the form of oscillating and propagating pressure waves.

The frequency of the waves are dependent on the frequency of the vibrating source. If the frequency of the vibrating source is high, then the sound wave will also have a high frequency. The sounds that we hear, from the voice of the person right next to you, to the music coming from your iPod earphones, to the crashing noise of shattered glass, all come from a vibrating source.

As the sound waves propagate through a medium, the pressure at a localized region in the medium alternates between compressions and rarefactions (or decompressions). Thus, if at one instant, a region in the medium experiences compression, the regions adjacent to it along the line of propagation are expected to be experiencing rarefactions.

Then as time progresses, the region in question undergoes a rarefaction while those adjacent to it undergo compressions. Therefore, if no medium exists, then the compressions and rarefactions cannot occur.

Now, how does one hear sounds? Remember how a source has to vibrate to produce a sound wave, and how a vibrating medium (e.g. air) has to exist to allow the sound wave to propagate? In the same manner, the receiver of the sound has to have something that can vibrate in order to ‘interpret’ the sound carried by the vibrating medium.

In the case of our ears, our eardrums serve as the receivers. When the vibrating air reaches our eardrums, it causes our eardrums to vibrate as well. The eardrums then transmit these vibrations to tiny bones in the middle ear, and so on until they reach the inner ear where the oscillating pressures are converted into electrical signals and sent to the brain.

Our ears are sensitive to vibrations between 20 to 20,000 Hz. Normally, frequencies that are higher or lower than the range provided cannot be processed by our auditory system. Young kids however, are able to hear slightly higher frequencies. That means, the range over which we are sensitive to diminishes as we grow older.

We have some articles in Universe Today that are related to sound. Here are two of them:

Hypersonic
Supersonic

Speed of sound references, brought to you by NASA. Here are the links:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Sources:
Indiana University
Wikipedia

March 30, 2010April 26, 2016 by Tega Jessa

Oxygen Cycle

The oxygen cycle is the cycle that helps move oxygen through the three main regions of the Earth, the Atmosphere, the Biosphere, and the Lithosphere. The Atmosphere is of course the region of gases that lies above the Earth’s surface and it is one of the largest reservoirs of free oxygen on earth. The Biosphere is the sum of all the Earth’s ecosystems. This also has some free oxygen produced from photosynthesis and other life processes. The largest reservoir of oxygen is the lithosphere. Most of this oxygen is not on its own or free moving but part of chemical compounds such as silicates and oxides.

The atmosphere is actually the smallest source of oxygen on Earth comprising only 0.35% of the Earth’s total oxygen. The smallest comes from biospheres. The largest is as mentioned before in the Earth’s crust. The Oxygen cycle is how oxygen is fixed for freed in each of these major regions.

In the atmosphere Oxygen is freed by the process called photolysis. This is when high energy sunlight breaks apart oxygen bearing molecules to produce free oxygen. One of the most well known photolysis it the ozone cycle. O2 oxygen molecule is broken down to atomic oxygen by the ultra violet radiation of sunlight. This free oxygen then recombines with existing O2 molecules to make O3 or ozone. This cycle is important because it helps to shield the Earth from the majority of harmful ultra violet radiation turning it to harmless heat before it reaches the Earth’s surface.

In the biosphere the main cycles are respiration and photosynthesis. Respiration is when animals and humans breathe consuming oxygen to be used in metabolic process and exhaling carbon dioxide. Photosynthesis is the reverse of this process and is mainly done by plants and plankton.

The lithosphere mostly fixes oxygen in minerals such as silicates and oxides. Most of the time the process is automatic all it takes is a pure form of an element coming in contact with oxygen such as what happens when iron rusts. A portion of oxygen is freed by chemical weathering. When a oxygen bearing mineral is exposed to the elements a chemical reaction occurs that wears it down and in the process produces free oxygen.

These are the main oxygen cycles and each play an important role in helping to protect and maintain life on the Earth.

If you enjoyed this article there are several other articles on Universe Today that you will like. There is a great article on the Carbon Cycle. There is also an interesting piece on Earth’s atmosphere leaking into space.

There are also some great resources online. There is a diagram of the oxygen cycle with some explanations on the NYU website. You should also check out the powerpoint slide lecture on the oxygen cycle posted on the University of Colorado web site.

You should also check out Astronomy Cast. Episode 151 is about atmospheres.

March 26, 2010April 26, 2016 by Jerry Coffey

Earth Surface

[/caption]Most of the Earth surface, about 70%, is covered with water. The remaining 30% is made up of the seven continental landmasses. Underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth’s surface layer is made of rock. This outer layer formed a hard, rocky crust as lava cooled about 4.5 billion years ago. This crust is broken into many large plates(tectonic plates) that move slowly relative to each other. The mountain ranges around the world formed when two plates collided and their edges are forced up. Many other surface features are the result of the movement of these tectonic plates. The plates move anywhere from 25 to 100 mm per year. About 250 million years ago most of the land was connected together.

The rocky layer under the soil of the Earth is called the crust. This comprises the continents and ocean basins. The crust has a variable thickness, being 35-70 km thick on the continents and 5-10 km thick in the ocean basins. The crust is composed mainly of alumino-silicates. The entire crust occupies just 1% of the Earth’s volume. The temperature of the crust increases as you go deeper into the Earth. It starts out cool, but can get up to 400 degrees C at the boundary between the crust and the mantle.

The tectonic plates are actually floating on the molten asthenosphere which is the lower mantle of the Earth. Earthquakes, volcanoes, mountains, and oceanic trench formation occur along plate boundaries. The plates are in constant motion. The reason that tectonic plates are able to move is the Earth’s lithosphere has a higher strength and lower density than the underlying asthenosphere. Their movement is dictated by heat dissipation from the Earth’s mantle. Lateral density variations in the mantle result in convection, which is transferred into plate motion through some combination of frictional drag, downward suction at the subduction zones, and variations in topography and density of the crust that result in differences in gravitational forces.

The Earth’s surface may seemed fixed and permanent to us, but underneath our feet there is constant motion and changes that we may not notice until there is an earthquake or a volcanic eruption. Here on Universe Today we have a great article with interesting facts about Earth. Astronomy Cast offers a good episode about plate tectonics. Here is the NASA webpage about Earth

References:
NASA Earth Observatory
NASA: Continents in Collision
NASA: Structure of the Earth

March 22, 2010December 24, 2015 by Jerry Coffey

Does The Sun Move?

The center of our Milky Way galaxy. Image credit: NASA.

[/caption]Does the Sun Move? What an interesting question. We mainly talk about everything in the solar system orbiting the Sun and celestial objects outside the solar system being in relation to the Sun. The answer to the question is : Yes. The Sun and the entire solar system orbits around the center of the Milky Way galaxy. The average velocity of the solar system is 828,000 km/hr. At that rate it will take about 230 million years to make one complete orbit around the galaxy.

You can check out these amazing books for more information about the Sun.

The Milky Way is a spiral galaxy. It is believed that it consists of a central bulge, 4 major arms, and several shorter arm segments. The Sun and the rest of our solar system is located near the Orion arm, between two major arms, Perseus and Sagittarius. The diameter of the Milky Way is about 100,000 light years and the Sun is located about 28,000 light-years from the Galactic Center. It has been suggested fairly recently that ours is actually a barred spiral galaxy. That means that instead of a bulge of gas and stars at the center, there is probably a bar of stars crossing the central bulge.

Everything in the known universe rotates on an axis and orbits something else in space. The Sun is no exception. Here is the NASA webpage about the sun’s movements through space. Astronomy Cast offers two good episodes: one is about the mysteries of the solar system and the other is about solar system movements.

March 22, 2010December 24, 2015 by Tega Jessa

Formula For Velocity

The formula for velocity is one of the first that you learn in physics. It is also one of the most important as it is help to solve more complex physic problems and give comprehension of other physics concepts. However it is one that can be easily misunderstood. We too often mistake speed and velocity to be the same. As we know it the formula simply states that velocity is rate of the change in position or distance over time. The problem is that this can also be applied to speed. However speed and velocity are to different concepts even though they share the same formula.

The first thing that sets velocity apart is that it is what is called a vector. A vector is a quantity that has both a numerical magnitude or value and a direction. Physics involving velocity needs these two components to work properly. Speed only has magnitude and no direction.

The next thing is that velocity can have a positive or negative value. This most times has to do with the direction of the object in its particular reference frame. This is because physics breaks down motion on the large scale from the point of view of an observer. Speed is different in that is relative to whatever circumstance it is applied to.

Finally velocity can vary over time. Derivations of the formula for velocity like the formula for final velocity take this into account taking an intial and final velocity to determine the overall velocity of an object. Speed only has one situation and that is instantaneous velocity or the speed that occurs at a given moment.

The formula for velocity is one of the key concepts of physics. Without it we can’t understand classical mechanics and even the motion of particles and massive planets and galaxies. For this reason it is important for any physics lover to understand how it works and should be applied.

If you enjoyed this article there are several others on Universe Today that you will find interesting. There is a great article about Newton’s laws of motion. There is also an interesting article on Planck’s constant.

You can also find some great resources online. There is a great explanation of velocity on the GSU.edu hyperphysics web site. You should also watch the video about motion on howstuffworks.com.

You can also listen Astronomy Cast. Episode 44 is about Einstein’s theory of general relativity.

Sources:
The Physics Classroom
Engineering Toolbox