Posted on by John Carl Villanueva

Charge of Electron

Charge of Electron
Simplified Scheme of Millikan’s Oil-drop Experiment

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The charge of the electron is equivalent to the magnitude of the elementary charge (e) but bearing a negative sign. Since the value of the elementary charge is roughly 1.602 x 10-19 coulombs (C), then the charge of the electron is -1.602 x 10-19 C.

When expressed in atomic units, the elementary charge takes the value of unity; i.e., e = 1. Thus, the electron’s charge can be denoted by -e. Although the proton is much more massive than the electron, it only has a charge of e. Hence, neutral atoms always bear the same number of protons and electrons.

JJ Thomson is the undisputed discoverer of the electron. However, despite all those experiments he performed on it, he could only manage to obtain the electron’s charge to mass ratio. The distinction of being the first to measure the electron’s charge goes to Robert Millikan through his oil-drop experiment in 1909.

The Millikan Oil-Drop Experiment

Here’s the basic idea. If you know the density and dimensions (thus subsequently the volume) of a substance, it’s going to be easy to calculate its mass and the force that gravity exerts on it, a.k.a. weight. If you recall, weight is just m x g.

Now let’s assume these substances to be charged oil drops. If you subject these drops to gravity alone, they’ll fall freely. However, if they are allowed to fall in a uniform electric field, their trajectory will be altered depending on the direction and magnitude of the field.

If the forces due to the field are directed opposite to gravity, the downward velocity of the particles may decrease. At some point, when the upward force is equal to the downward force, the velocities may even go down to zero and the particles will stay in mid-air.

At this specific instance, if we know the magnitude of the electric field (in N/C, units defining the force per unit charge) and the weight of each particle, we can calculate the force of the electric field on a single particle and finally derive the charge.

Thus, a basic Millikan Oil-Drop Experiment setup will include an enclosure containing falling charged oil drops, a device to measure their radii, an adjustable uniform electric field, and a meter to determine the field’s magnitude.

By repeating the experiment on a large number of oil drops, Millikan and his colleague, Harvey Fletcher, obtained electron charge values within 1% of the currently accepted one.

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

Physics World also has some more:

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:
Wikipedia
GSU Hyperphysics
University of Alaska-Fairbanks

Posted on by John Carl Villanueva

What is the Oscillating Universe Theory?

The Oscillating Universe Theory is a cosmological model that combines both the Big Bang and the Big Crunch as part of a cyclical event. That is, if this theory holds true, then the Universe in which we live in exists between a Big Bang and a Big Crunch.

In other words, our universe can be the first of a possible series of universes or it can be the nth universe in the series.

As we know, in the Big Bang Theory, the Universe is believed to be expanding from a very hot, very dense, and very small entity. In fact, if we extrapolate back to the moment of the Big Bang, we are able to reach a point of singularity characterized by infinitely high energy and density, as well as zero volume.

This description would only mean one thing – all the laws of physics will be thrown out of the window. This is understandably unacceptable to physicists. To make matters worse, some cosmologists even believe that the Universe will eventually reach a maximum point of expansion and that once this happens, it will then collapse into itself.

This will essentially lead to the same conditions as when we extrapolate back to the moment of the Big Bang. To remedy this dilemma, some scientists are proposing that perhaps the Universe will not reach the point of singularity after all.

Instead, because of repulsive forces brought about by quantum effects of gravity, the Universe will bounce back to an expanding one. An expansion (Big Bang) following a collapse (Big Crunch) such as this is aptly called a Big Bounce. The bounce marks the end of the previous universe and the beginning of the next.

The probability of a Big Bounce, or even a Big Crunch for that matter, is however becoming negligible. The most recent measurements of the CMBR or cosmic microwave background radiation shows that the Universe will continue on expanding and will most likely end in what is known as a Big Freeze or Heat Death.

CMBR readings are currently being gathered by a very accurate measuring device known as the WMAP or Wilkinson Microwave Anisotropy Probe. It is the same device that has measured with sharp precision the age of our universe. It is therefore highly unlikely that future findings will deviate largely from what has been discovered regarding the Universe’s expansion now.

There is however one mysterious entity whose deeper understanding of may change the possibilities. This entity, known as dark energy, is believed to be responsible for pushing the galaxies farther apart and subsequently the universe’s accelerated expansion. Unless its actual properties are very dissimilar from what it is showing now, we may have to shelve the Oscillating Universe Theory.

We’ve got a few articles that touch on the Oscillating Universe Theory here in Universe Today. Here are two of them:

Physics World also has some more:

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:
PBS.org
Wikipedia

Posted on by Fraser Cain

Which Planet Has the Most Moons?

Jupiter and its moons. Image credit: NASA/JPL

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The planet with the most moons in the Solar System is Jupiter, with a total of 63 confirmed moons (as of 2009). Of course, it’s always possible that more moons will be discovered orbiting Jupiter in the future, and that number will go up.

Eight of Jupiter’s moons are regular satellites, with 4 large, spherical moons, and 4 smaller moons that orbit closer to Jupiter. Jupiter has an additional 55 tiny irregular satellites.

The planet with the second highest number of moons is Saturn, with 61 moons. With such a close total, more moons could easily be discovered circling the rings planet, and push its total higher.

The next planet with a high number of moons is Uranus, with 27 known moons.

This is followed by Neptune with 13 moons, Mars with 2 moons, and then Earth with its single moon.

Mercury and Venus have no moons. Although Pluto isn’t a planet anymore, it does have a total of 3 moons.

We have written many articles about moons in the Solar System. Here’s an article about the largest moon in the Solar System, and here’s an article about how many moons there are in total in the Solar System.

Here’s an article from NASA about Jupiter’s moons, and here’s Hubblesite’s News Releases about Jupiter.

We have recorded a whole episode of Astronomy Cast just about Jupiter’s moons. Listen to it here.

Posted on by Fraser Cain

How Many Rings Does Uranus Have?

Uranus with its moons and rings. Image credit: Hubble

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Here’s a question, how many rings does Uranus have? Well, as of 2008, the total number of rings circling Uranus is 13.

The rings of Uranus were first discovered in 1977 by astronomers James Elliot, Edward Dunham and Douglas Mink. When he first discovered Uranus 200 years before, William Herschel reported seeing rings around Uranus, but his telescope probably wasn’t powerful enough to reveal them. Additional rings were discovered in 1986 when NASA’s Voyager 2 spacecraft made its flyby, and then two more outer rings were turned up by the Hubble Space Telescope in 2003-2005.

The rings of Uranus are dark and opaque, with a very low albedo. Astronomers believe that they’re made of water ice mixed with organic molecules. Unlike Saturn’s rings, the rings of Uranus are very narrow; just a few kilometers wide.

Uranus’ rings consist of 3 major groups. There are the narrow main rings, the dusty rings, and the newly discovered outer ring system.

Astronomers think that the rings of Uranus are being shepherded by small moons in the ring system. Without these shepherd moons, the rings of Uranus would spread out radially and dissipate into space. It’s also believed that there’s some process that’s replenishing the ice particles in the rings; perhaps collisions between icy objects in the rings.

I mentioned at the beginning of the article that current ring count stands at 13; however, that’s for 2008. With improved technology and telescopes, astronomers could turn up more rings in the future, so stay tuned.

We have written many articles about Uranus for Universe Today. Here’s an article about the discovery of new rings and moons around Uranus, and here’s an image of a blue ring around Uranus.

Here’s NASA’s Solar System Exploration Guide on the rings of Uranus, and here’s NASA’s fact sheet on the rings.

We have also recorded an entire episode of Astronomy Cast just about Uranus. Check it out here.

Posted on by Fraser Cain

Who Discovered Venus?

Venus captured by Magellan.

Venus is easy to see with the unaided eye. In fact, it’s the brightest object in the night sky after the Moon, so it’s safe to say that humans have been aware of Venus since people have looked to the skies. In fact, there are 5 planets visible with the unaided eye: Mercury, Venus, Mars, Jupiter and Saturn. It’s actually impossible to say who discovered Venus, since the planet has been known since before recorded history. Humans have been on Earth for 200,000 years, so maybe that’s how long we’ve known about the planet.

But ancient astronomers didn’t really know what Venus was. They knew it was an object that moved in the sky from night to night, sometimes being obscured by the glare of the Sun. But it wasn’t until Copernicus developed his model of the Solar System that placed the Sun at the center, and the planets orbiting it. At that point, both Venus and Earth were recognized to be planets.

Galileo pointed his telescope at Venus in 1610, and confirmed Copernicus’ theory by showing that Venus went through distinct phases, just like the Moon. The phases matched the predictions made by Copernicus, and demonstrated that Venus was really a planet, orbiting the Sun and not the Earth.

This model was confirmed even more when Venus made a transit across the surface of the Sun on December 4, 1639. The most recent transit of Venus happened in 2004, and the next one will occur in 2012.

Even in the best telescopes we have today, the surface of Venus is obscured by thick clouds, so it’s impossible to see any features on its surface. It wasn’t until radar signals were bounced off Venus in 1961 that scientists had any way to calculate the planet’s speed of rotation and axial tilt.

The first spacecraft to visit Venus was Mariner 2, but more recent spacecraft, like NASA’s Magellan were equipped with radar instruments that can peer through the thick atmosphere of Venus and reveal the hellish surface below.

Spacecraft have even landed on the surface of Venus. The Russian Venera program put a handful of landers on the surface of Venus, which were able to send home images of the surface before they malfunctioned in the incredible heat and pressure found on the surface of the planet.

We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s a link to NASA’s Solar System Exploration Guide on Venus.

We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.

References:
NASA: Transit of Venus
NASA Solar System Exploration: Venus

Posted on by Fraser Cain

How Many Rings Does Saturn Have?

Saturn's Rings. Image credit: NASA/JPL/SSI

Saturn is best known for its elaborate ring system. They’re made of icy particles orbiting the planet. The rings have distinct divisions, and astronomers have separate designations for each of Saturn’s rings. But how many rings does Saturn have?

The question is actually impossible to answer. Saturn has more than a dozen rings and gaps within the rings – and more are being discovered by spacecraft like NASA’s Cassini. But the planet does have several major ring systems and gaps within them.

The two densest parts of the rings are the A and B rings, separated by the Cassini Division, and then the C Ring. So, is that 3 rings, or 4? Whatever the case, these comprise Saturn’s main rings.

After the 3 main rings, you have the smaller, dusty rings: the D Ring, G Ring, E Ring, and others beyond that. There’s also the F Ring, which is just outside the A Ring.

That’s 3 main rings and 5 dusty rings for a total of 8 rings, 9 if you count the Cassini Division.

But there are even more rings around Saturn. There’s the Janus Ring, the Methone Ring Arc, the Anthe Ring Arc and the Pallene Ring, as well as the Roche Division. 4 more rings and another division.

That brings us to 12 rings and 2 divisions.

But then there are also smaller divisions and gaps within the various rings that would bring the total to more than 30 (the Encke Gap, the Huygens Gap, the Dawes Gap, and many more).

To answer the question, how many rings does Saturn have, you really need to find out how closely you’re looking. From what you might be able to see, there are 3 rings. With powerful telescopes, you can make out 8 rings. And with spacecraft like Cassini orbiting Saturn, that total rises above 30.

We have written many articles about Saturn’s rings for Universe Today. Here’s an article about a time when Saturn’s rings were disappearing, and here’s an article about vertical structures that tower above Saturn’s rings.

Here’s the same question answered by Ask an Astronomer. Here’s an easier question, how many moons does Saturn have?

We have done an entire episode of Astronomy Cast all about Saturn. Give it a listen.

Reference:
NASA

Posted on by Fraser Cain

Milky Way Galaxy Pictures

Artist impression of the Milky Way. Image credit: NASA

Here are some beautiful pics of the Milky Way Galaxy. It’s important to remember that we live inside the Milky Way Galaxy, so there’s no way to show a true photograph of what the Milky Way looks like. We can see pictures of the Milky Way from inside it, or see artist illustrations of what the Milky Way might look like from outside.

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This Milky Way Galaxy picture shows what our galaxy would look like from above. You can see its spiral arms, dense core and the thin halo. The Milky Way is a common barred spiral galaxy. There are billions more just like it in the Universe.

Milky Way in infrared. Image credit: COBE
Milky Way in infrared. Image credit: COBE

This picture of the Milky Way was captured by NASA’s COBE satellite. This photograph was taken using the infrared spectrum, which allows astronomers to peer through the gas and dust that normally obscures the center of the Milky Way.

The plane of the Milky Way, recorded with the Chandra satellite in three colours: Photons with energies between 0.5 and 1keV appear red, those between 1 and 3keV green, and those between 3 and 7keV blue. Discrete sources are indicated by circles. Image: Mikhail Revnivtsev
The plane of the Milky Way, recorded with the Chandra satellite in three colours: Photons with energies between 0.5 and 1keV appear red, those between 1 and 3keV green, and those between 3 and 7keV blue. Discrete sources are indicated by circles. Image: Mikhail Revnivtsev

This image of the Milky Way Galaxy was taken with the Chandra X-Ray Observatory, which can see in the X-Ray spectrum. In this view, only high energy emissions are visible, such as the radiation emitted from black holes and other high energy objects.

Artist's concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way.Credit: NASA, ESA, and A. Schaller (for STScI)
Artist's concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way.Credit: NASA, ESA, and A. Schaller (for STScI)

Here’s an artist’s impression of what a galaxy like the Milky Way might have looked like early in its history. This image shows a supermassive black hole with young blue stars circling it.

Milky_Way_infrared_mosaic. Credit: Spitzer Space Telescope
Milky_Way_infrared_mosaic. Credit: Spitzer Space Telescope

This is a mosaic image of the Milky Way captured by NASA’s Spitzer Space Telescope. It was built up by several photographs taken by Spitzer, which sees in the infrared spectrum, and can peer through obscuring dust.

Posted on by Abby Cessna

What Are Planets?

The mysterious Eris and moons. Credit: NASA

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Throughout history, the definition of what a planet is has changed and meant various things at the same time depending on who was defining it. Objects like the Sun, which we would now scoff at defining as a planet, was once considered just that, and so was the Moon. Ceres, discovered in 1801, was originally thought to be a planet until astronomer discovered Pallas that has a similar orbit. Astronomers, even using the technology of their time, were able to tell that these objects were not planets. The famous astronomer Sir William Herschel suggested the name “asteroids” which stuck. Asteroids were then accepted as a distinct category.

Several years ago, you may have said that a planet is one of the nine large celestial bodies that orbits the Sun. However, new technology, which made the discovery of many new celestial bodies in various regions, such as the Kuiper Belt, possible also made determining what a planet is more difficult. While a number of people suggested various definitions over the years, none of them were widely accepted.

The issue came to a head in 2005 when an object larger than Pluto is was discovered beyond the Kuiper Belt. This object, which is now called Eris, was a source of division among many. Some astronomers wanted Eris to be the tenth planet while others considered it to be just another asteroid, despite the fact that it is larger than Pluto is. The International Astronomical Union (IAU), which usually resolves disputes like this, met in 2005 at a conference, but despite debating the issue, they did not come up with an agreed upon definition. The matter was resumed in summer of 2006 at the next IAU conference.

In August 2006, the IAU finally agreed upon a definition for a planet. The IAU’s official definition was, “A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.” An object that has cleared the neighborhood of its orbit is of sufficient size for its gravity to force other objects of similar size out of its orbit. In addition to defining what a planet is, the IAU also created a new category of dwarf planets, which Pluto was reclassified as, and Eris and several other objects were also put in that category. The definition has had severe opposition, especially with many people angry at the demotion of Pluto.

Universe Today has articles on dwarf planets and planet.

For more information, try an overview of the planets and what is a planet.

Astronomy Cast has episodes on all the planets including Venus.

Posted on by Abby Cessna

Solar System Projects for Kids

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Discovery Education has eight projects on the Solar System that you can do with a class or a single child. Many of them are also great projects for a science fair or a report. This website also has games to play and some ideas on how to get your students or children interested in space as well as a quiz to make sure that the material has been mastered.

Cool Science Projects has some suggestions on various  projects for a science fair as well as some background material on the Solar System.

Enchanted Learning has a number of Solar System crafts that are simple enough for young children probably in kindergarten or grades 1 through 3. There are also coloring pages about the Solar System that can be printed.

The AOK Corral has a project painting a glow in the dark Solar System, which is a great twist on an old classic. You can take the idea of using the glow in the dark paint a step further and create a glow in the dark mural for a kid’s room.

How Stuff Works has some great projects for kids including one on how to make your own planetarium and learning how to create your own astrolabe.

A to Z Home’s Cool Homeschooling has a ton of links to great projects and experiments you can try. Some of these links let you figure out your weight on other planets. You can also get information on all the planets in the Solar System.

One of the best resources for your space needs is NASA. NASA has materials for children including games to play and projects for science fairs as well as information on the planets and all the other objects in the Solar System. They also have materials for children of different ages and even resources for college students. NASA even has information on how to get a guest speaker from NASA at your school.

Universe Today has articles on what the Solar System is and all the planets.

For more information check out an overview of the Solar System and the Solar System for kids.

Astronomy Cast has episodes on all the planets including Jupiter.

Posted on by John Carl Villanueva

Interesting Facts About the Universe

WMAP 5 year full sky

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So you think you know your universe? We’ve got our own top 10 list on the most interesting facts about the Universe.

1. It was hot when it was young

The most widely accepted cosmological model is that of the Big Bang. This was proven since the discovery of the cosmic microwave background radiation or CMBR. Although, strictly speaking, no one knows exactly what ‘banged’, we know from extrapolation that the Universe was infinitely hot at birth, cooling down as it expanded.

In fact, even only within minutes of expansion, scientists predict its temperature to have been about a billion Kelvin. Moving backward to 1 second, it is said to have been at 10 billion Kelvin. For comparison, today’s universe is found to have an average temperature of only 2.725 Kelvin.

2. It will be cold when it grows old

Observations made especially on galaxies farthest from us show that the Universe is expanding at an accelerated rate. This, and data that show that the Universe is cooling allows us to believe that the most probable ending for our universe is that of a Big Freeze.

That is, it will be devoid of any usable heat (energy). It is due to this prediction that the Big Freeze is also known as the Heat Death.Accurate measurements made by the Wilkinson Microwave Anisotropy Probe (WMAP) on the current geometry and density of the Universe favor such an ending.

3. The Universe spans a diameter of over 150 billion light years

Current estimates as with regards to the size of the Universe pegs it at a width of 150 billion light years. Although it may seem peculiarly inconsistent with the age of the Universe, which you’ll read about next, this value is easily understood once you consider the fact that the Universe is expanding at an accelerated rate.

4. The Universe is 13.7 billion years old

If you think that is amazing, perhaps equally remarkable is the fact that we know this to better than 1% precision. Credit goes to the WMAP team for gathering all the information needed to come up with this number. The information is based on measurements made on the CMBR.

Older methods which have contributed to confirming this value include measurements of the abundances of certain radioactive nuclei. Observations made on globular clusters, which contain the oldest stars, have also pointed to values close to this.

5. The Earth is not flat – but the Universe is

Based on Einstein’s Theory of General Relativity, there are three possible shapes that the Universe may take: open, closed, and flat. Once again, measurements by WMAP on the CMBR have revealed a monumental confirmation – the Universe is flat.

Combining this geometry and the idea of an invisible entity known as dark energy coincides with the widely accepted ultimate fate of our universe, which as stated earlier, is a Big Freeze.

6. Large Scale Structures of the Universe

Considering only the largest structures, the Universe is made up of filaments, voids, superclusters, and galaxy groups and clusters. By combining galaxy groups and clusters, we come up with superclusters. Some superclusters in turn form part of walls, which are also parts of filaments.

The vast empty spaces are known as voids. That the Universe is clumped together in certain parts and empty in others is consistent with measurements of the CMBR that show slight variations in temperature during its earliest stages of development.

7. A huge chunk of it is made up of things we can’t see

Different wavelengths in the electromagnetic spectrum such as those of radio waves, infrared, x-rays, and visible light have allowed us to peer into the cosmos and ‘see’ huge portions of it. Unfortunately, an even larger portion cannot be seen by any of these frequencies.

And yet, certain phenomena such as gravitational lensing, temperature distributions, orbital velocities and rotational speeds of galaxies, and all others that are evidence of a missing mass justify their probable existence. Specifically, these observations show that dark matter exists. Another invisible entity known as dark energy, is believed to be the reason why galaxies are speeding away at an accelerated rate.

8. There is no such thing as the Universe’s center

Nope. The earth is not the center of the Universe. It’s not even the center of the galaxy. And no again, our galaxy is not the entire universe, neither is it the center. Don’t hold your breath but the Universe has no center. Every galaxy is expanding away from one another.

9. Its members are in a hurry to be as far away from each other as possible

The members that we are talking about are the galaxies. As mentioned earlier, they are rushing away from each other at increasing rates. In fact, prior to the findings of most recently gathered data, it was believed that the Universe might end in a Big Rip. That is, everything, down to the atoms, would be ripped apart.

This idea stemmed from this observed accelerated rate of expansion. Scientists who supported this radically catastrophic ending believed that this kind of expansion would go on forever, and thus would force everything to be ripped apart.

10. To gain a deeper understanding of it, we need to study structures smaller than the atom

Ever since cosmologists started to trace events backward in time based on the Big Bang model, their views, which focused only on the very large, got smaller and smaller. They knew, that by extrapolating backward, they would be led into a universe that was very hot, very dense, very tiny, and governed by extremely high energies.

These conditions were definitely within the realm of particle physics, or the study of the very small. Hence, the most recent studies of both cosmology and particle physics saw an inevitable marriage between the two.

There you have it. Feel free to come up with a longer list of your own.

Sources:
UT-Knoxville
NASA WMAP
NASA: Age of the Universe
NASA: Shape of the Universe
UCLA: Center of the Universe
Hubblesite: Fate of the Universe