Astronomy Archives

November 25, 2009December 24, 2015 by Sean Welton

Tips for Viewing the Geminid Meteor Shower

Occurring every year in mid-December, the Geminid meteor shower is commonly referred to as the most reliable meteor shower of the year. That is, it almost always puts on a great show!

The Geminid meteor shower is sure to be a stunning show this year, as the Moon will not be visible at night, so its glow will not impede your meteor viewing ability. In addition, the Geminids’ radiant is favorably positioned for most viewers at this time of year. In order to see the most meteors, I suggest the following tips:

The Geminid meteor shower has a very broad maximum peak. Because of this, the night on which you view the meteors isn’t critical. You will of course, see more meteors on the peak nights. This year the Geminid meteor shower’s peak is the night of December 13th-14th, 2009.
The best time to view a meteor shower is in the late night to early morning hours. The best time to view a meteor shower typically begins around 2 AM. This is because as the Earth rotates toward dawn, the forward velocity of the planet adds to the linear velocity of the surface and atmosphere. This has the effect of “sweeping up” more meteors.
If you’re not normally awake at 2 AM, like many people, simply go to sleep very early and set an alarm clock to wake you up to view the meteor shower. Trust me on this point, it is definitely worth it.
The Geminid meteor shower’s radiant is right near the twin bright stars Castor and Pollux in Gemini. Click the image at top right to see a map (thanks to Stellarium). The trick, however, isn’t to look towards the radiant, but to keep your eyes on the whole sky. While it’s impossible to look at the whole sky, just keep your eyes scanning and alert. This increases your chances of seeing a fleeting meteor or one out of the corner of your eye.
Darkness is key to proper meteor shower viewing. If you live in a city or other light polluted area, try going to a dark sky site to truly experience a meteor shower. You might be surprised how close a dark sky site is to you! Here are some tips on finding a dark sky near you.
Dress warm! The cold December air will seem extra cold, since you’ll be sitting outside, inactive for the most part. I also have some tips on cold-weather astronomy at Visual Astronomy. If you are too cold, go inside for a bit! Your safety is not worth seeing some meteors!
Keep comfortable, too! I’ve found the best way to watch meteor showers is either laying down in a sleeping bag, or on an Adirondack or other reclining lawn chair. This allows you to keep your eyes on the sky without straining your neck!
Keep safe! If you’re traveling to an unknown or unfamiliar area to watch the meteor shower, don’t travel alone! Take a buddy with you. Not only is this great for safety, but meteor showers should be a social event, and are fun to share with a friend!
Green lasers are great for pointing out celestial objects. I use one to point out objects to people, and it works much better than trying to point with your hand. Just be careful with it and do not use a laser more powerful than 5 mW.
Finally, if you’re feeling ambitious, take pictures! This is a real challenge, but if you’re up to it, it’s a very rewarding challenge. You’ll need a tripod and a camera that can take long exposures. Set your exposure for somewhere around 30 seconds and let it record the whole sky. If a meteor crosses the field of view, it will be captured, and you can keep it forever!

So using these tips, you can get the most out of your Geminid viewing experience!

November 25, 2009December 24, 2015 by Mike Simonsen

Eta Carinae- A Naked Eye Enigma

Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI

[/caption]

Eta Carinae is a beast of a star. At more than 100 solar masses and 4 million times the luminosity of our Sun, eta Car balances dangerously on the edge of stellar stability and it’s ultimate fate: complete self-destruction as a supernova. Recently, Hubble Space Telescope observations of the central star in the eta Carinae Nebula have raised an alert on eta Car among the professional community. What they discovered was totally unexpected.

“It used to be, that if you looked at eta Car you saw a nebula and then a faint little core in the middle” said Dr. Kris Davidson, from the University of Minnesota. “Now when you look at it, it’s basically the star with a nebula. The appearance is completely different. The light from the star now accounts for more than half the total output of eta Car. I didn’t expect that to happen until the middle of this century. It’s decades ahead of schedule. We know so little about these very massive objects, that if eta Car becomes a supernova next Thursday we should not be very surprised.”

In 1843, eta Carinae underwent a spectacular eruption, making it the second brightest star in the sky behind Sirius. During this violent episode, eta Car ejected 2 to 3 solar masses of material from the star’s polar regions. This material, traveling at speeds close to 700 km/s, formed two large, bipolar lobes, now known as the Homunculus Nebula. After the great eruption, Eta Car faded, erupted again briefly fifty years later, then settled down, around 8^th magnitude. Davidson picks up the story from there.

This light curve depicts the visual apparent brightness of Eta Car from 1822 to date. It contains visual estimates (big circles), photographic (squares), photoelectric (triangles) and CCD (small circles) observations. All of them have been fitted for consistency of the whole data. Red points are recent observations from La Plata (Feinstein 1967; Fernández-Lajús et al., 2009, 2010). Used by permission.

“Around 1940, Eta suddenly changed its state. The spectrum changed and the brightness started to increase. Unfortunately, all this happened at a time when almost no one was looking at it. So we don’t know exactly what happened. All we know is that by the 1950’s, the spectrum had high excitation Helium lines in it that it didn’t have before, and the whole object, the star plus the Homunculus, was gradually increasing in brightness. In the past we’ve seen three changes of state. I suspect we are seeing another one happening now.”

During this whole time eta Car has been shedding material via its ferocious stellar winds. This has resulted in an opaque cloud of dust in the immediate vicinity of the star. Normally, this much dust would block our view to the star. So how does Davidson explain this recent, sudden increase in the luminosity of eta Carinae?

“The direct brightening we see is probably the dust being cleared away, but it can’t be merely the expansion of the dust. If it’s clearing away that fast, either something is destroying the dust, or the stellar wind is not producing as much dust as it did before. Personally, I think the stellar wind is decreasing, and the star is returning to the state it was in more than three hundred years ago. In the 1670’s, it was a fourth magnitude, blue, hot star. I think it is returning to that state. Eta Carinae has just taken this long to readjust from its explosion in the 1840’s.”

After 150 years what do we really know about one of the great mysteries of stellar physics? “We don’t understand it, and don’t believe anyone who says they do,” said Davidson. “The problem is we don’t have a real honest-to-God model, and one of the reasons for that is we don’t have a real honest-to-God explanation of what happened in 1843.”

Can amateur astronomers with modest equipment help untangle the mysteries of eta Carinae? Davidson think so, “The main thing is to make sure everyone in the southern hemisphere knows about it, and anyone with a telescope, CCD or spectrograph should have it pointed at eta Carinae every clear night.”

November 25, 2009December 24, 2015 by Steve Nerlich

The View from Down Under

Something that baffled me throughout my childhood, growing up in Australia, was the frequent references to the Man in the Moon, in children’s books and other popular media. I just couldn’t see it.

Only in my adult years have I put two and two together and realized that all those references were made by people from the Northern Hemisphere.

South of the equator we really are down under, even in astronomical terms. All the stuff you can see in the night sky around the celestial equator and the ecliptic we can see too, but it’s all upside down (or from our point of view, right side up).

So the lunar maria you see on the Moon’s surface, we can see too, but upside down none of it looks anything like a human face.

And Orion’s Belt? Nope, don’t get that either. What we see is an asterism we like to call ‘the Saucepan’ because what you see as a dagger hanging off a belt, we see as a handle rising from a pot.

We’ve also got our own down under Aurora Australis, although you’d have to climb a mountain in Tasmania, or even better catch an icebreaker to Antarctica, to see it.

But look, I’m envious. You’ve got a pole star, Polaris, which we never get to see. And you get a good view of the Andromeda Galaxy, which just barely peeks over our northern horizon around summer.

Down under, we have to use the Southern Cross to find the southern celestial pole. The Cross contains some of the southern sky’s brightest stars. During the winter months when it’s high in the sky, it’s generally the first group of stars to become visible after sunset, along with the nearby Pointer stars – which are actually Alpha and Beta Centauri.

The Southern Cross is kite-shaped and if you draw a line out from the kite’s long axis and another line out from between the Pointers, those two lines meet at the southern celestial pole. From there, just drop your hand straight down to the horizon and you are pointing due South. Cheaper than a compass.

We also have a couple of dwarf galaxies to look at, being the Large and Small Magellanic Clouds. OK, they are much smaller than Andromeda, but they are also a lot closer and hence appear much bigger. To the naked eye, they really do look like a couple of faint, wispy clouds.

For most southern sky observers, the Magellanic Clouds and the Southern Cross are circumpolar, slowly spinning around the southern celestial pole each night without ever setting.

You probably know that the story about how water spirals down the plug hole in opposite directions on either side of the equator is just urban myth. But it is the case that while stars in the Northern Hemisphere appear to spin slowly around Polaris in an anti-clockwise direction, all our stars spin around the southern celestial pole in a clockwise direction.

It’s true – fair dinkum.

November 24, 2009April 26, 2016 by Jean Tate

Quintessence

Quintessence is one idea – hypothesis – of what dark energy is (remember that dark energy is the shorthand expression of the apparent acceleration of the expansion of the universe … or the form of mass-energy which causes this observed acceleration, in cosmological models built with Einstein’s theory of general relativity).

The word quintessence means fifth essence, and is kinda cute … remember Earth, Water, Fire, and Air, the ‘four essences’ of the Ancient Greeks? Well, in modern cosmology, there are also four essences: normal matter, radiation (photons), cold dark matter, and neutrinos (which are hot dark matter!).

Quintessence covers a range of hypotheses (or models); the main difference between quintessence as a (possible) explanation for dark energy and the cosmological constant Λ (which harks back to Einstein and the early years of the 20th century) is that quintessence varies with time (albeit slooowly), and can also vary with location (space). One version of quintessence is phantom energy, in which the energy density increases with time, and leads to a Big Rip end of the universe.

Quintessence, as a scalar field, is not the least bit unusual in physics (the Newtonian gravitational potential field is one example, of a real scalar field; the Higgs field of the Standard Model of particle physics is an example of a complex scalar field); however, it has some difficulties in common with the cosmological constant (in a nutshell, how can it be so small).

Can quintessence be observed; or, rather, can quintessence be distinguished from a cosmological constant? In astronomy, yes … by finding a way to observed (and measure) the acceleration of the universe at widely different times (quintessence and Λ predict different results). Another way might be to observe variations in the fundamental constants (e.g. the fine structure constant) or violations of Einstein’s equivalence principle.

One project seeking to measure the acceleration of the universe more accurately was ESSENCE (“Equation of State: SupErNovae trace Cosmic Expansion”).

In 1999, CERN Courier published a nice summary of cosmology as it was understood then, a year after the discovery of dark energy The quintessence of cosmology (it’s well worth a read, though a lot has happened in the past decade).

Universe Today articles? Yep! For example Will the Universe Expand Forever?, More Evidence for Dark Energy, and Hubble Helps Measure the Pace of Dark Energy.

Astronomy Cast episodes relevant to quintessence include What is the universe expanding into?, and A Universe of Dark Energy.

Source: NASA

November 23, 2009December 24, 2015 by Nancy Atkinson

Baby Brown Dwarfs Provide Clues to Solve Mystery

Why – and how — do brown dwarfs form? Since these cosmic misfits fall somewhere between planets and stars in terms of their temperature and mass, astronomers haven’t yet been able to determine how they form: are their beginnings like planets or stars? Now, the Spitzer Space Telescope has found what could be two of the youngest brown dwarfs. While astronomers are still looking to confirm the finding of these so-called “proto brown dwarfs” it has provided a preliminary answer of how these unusual stars form.

The baby brown dwarfs were found in Spitzer data collected in 2005. Astronomers had focused their search in the dark cloud Barnard 213, a region of the Taurus-Auriga complex well known to astronomers as a hunting ground for young objects.

“We decided to go several steps back in the process when (brown dwarfs) are really hidden,” said David Barrado of the Centro de Astrobiología in Madrid, Spain, lead author of the paper, published in the Astronomy & Astrophysics journal. “During this step they would have an (opaque) envelope, a cocoon, and they would be easier to identify due to their strong infrared excesses. We have used this property to identify them. This is where Spitzer plays an important role because Spitzer can have a look inside these clouds. Without it this wouldn’t have been possible.”

Barrado said the findings potentially solve the mystery about whether brown dwarfs form more like stars or planets. The team’s findings? Brown dwarfs form like low-mass stars.

Brown dwarfs are cooler and more lightweight than stars and more massive (and normally warmer) than planets. They are born of the same dense, dusty clouds that spawn stars and planets. But while they may share the same galactic nursery, brown dwarfs are often called “failed” stars because they lack the mass of their hotter, brighter stellar siblings. Without that mass, the gas at their core does not get hot enough to trigger the nuclear fusion that burns hydrogen — the main component of these molecular clouds — into helium. Unable to ignite as stars, brown dwarfs end up as cooler, less luminous objects that are more difficult to detect — a challenge that was overcome in this case by Spitzer’s heat-sensitive infrared vision.

This artist's rendering gives us a glimpse into a cosmic nursery as a star is born from the dark, swirling dust and gas of this cloud. Image credit: NASA/JPL-Caltech

Young brown dwarfs also evolve rapidly, making it difficult to catch them when they are first born. The first brown dwarf was discovered in 1995 and, while hundreds have been found since, astronomers had not been able to unambiguously find them in their earliest stages of formation until now.

Spitzer’s longer-wavelength infrared camera penetrated the dusty natal cloud to observe STB213 J041757. The data, confirmed with near-infrared imaging from Calar Alto Observatory in Spain, revealed not one but two of what would potentially prove to be the faintest and coolest brown dwarfs ever observed.

The twins were observed from around the globe, and their properties were measured and analyzed using a host of powerful astronomical tools. One of the astronomers’ stops was the Caltech Submillimeter Observatory in Hawaii, which captured the presence of the envelope around the young objects. That information, coupled with what they had from Spitzer, enabled the astronomers to build a spectral energy distribution — a diagram that shows the amount of energy that is emitted by the objects in each wavelength.

From Hawaii, the astronomers made additional stops at observatories in Spain (Calar Alto Observatory), Chile (Very Large Telescopes) and New Mexico (Very Large Array). They also pulled decade-old data from the Canadian Astronomy Data Centre archives that allowed them to comparatively measure how the two objects were moving in the sky. After more than a year of observations, they drew their conclusions.

“We were able to estimate that these two objects are the faintest and coolest discovered so far,” Barrado said. This theory is bolstered because the change in brightness of the objects at various wavelengths matches that of other very young, low-mass stars.

While further study will confirm whether these two celestial objects are in fact proto brown dwarfs, they are the best candidates so far, Barrado said. He said the journey to their discovery, while difficult, was fun. “It is a story that has been unfolding piece by piece. Sometimes nature takes its time to give up its secrets.”

Lead image caption: This image shows two young brown dwarfs, objects that fall somewhere between planets and stars in terms of their temperature and mass. Image credit: NASA/JPL-Caltech/Calar Alto Obsv./Caltech Sub. Obsv.

Source: JPL

November 20, 2009December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast – November 20 -22, 2009

Greetings, fellow SkyWatchers! Yep. The Moon is back, but this weekend can still present some great opportunities for enjoying astronomy. If you’re up early or out late? Well, hey… The Leonid meteor shower is still producing activity! Why not take a few minutes to learn about a great variable star you can follow without optical aid or study a new lunar feature? There’s plenty to do for binoculars and small telescopes – and perhaps even a clever new study you haven’t looked at yet! Whenever you’re ready, I’ll see you in the dark…

Friday, November 20, 2009 – Today celebrates the birth of a significant astronomer, Edwin Hubble. Born on this date in 1889, Hubble became the first American astronomer to identify Cepheid variables in M31, which in turn established the extragalactic nature of the spiral nebulae. Continuing with the work of Carl Wirtz, and using Vesto Slipher’s redshifts, Hubble could then calculate the velocity–distance relation for galaxies. This has become known as Hubble’s Law and demonstrates the expansion of our universe.

Tonight we’ll pass the Moon and head just a little more than a fist-width west of the westernmost bright star in Cassiopeia, to have a look at Delta Cephei (RA 22 29 10 Dec +58 24 54). This is the most famous of all variable stars and the granddaddy of all Cepheids. Discovered in 1784 by John Goodricke, its changes in magnitude are not due to a revolving companion but rather the pulsations of the star itself.

Ranging over almost a full magnitude in 5 days, 8 hours, and 48 minutes precisely, Delta’s changes can easily be followed by comparing it to nearby Zeta and Epsilon. Upon reaching its dimmest point, it will brighten rapidly in a period of about 36 hours yet take 4 days to slowly dim again. Take time out of your busy night to watch Delta change and change again. It’s only 1,000 light-years away and doesn’t even require a telescope! (But even binoculars will show its optical companion.)

Saturday, November 21, 2009 – Tonight let’s go to the southern lunar cusp to identify two small but very nice craters. Using previous study Fabricus, continue south and look for the pair connected side-to-side rather than end-to-end.

This is crater Watt, with Steinheil intruding on it. Remember the distance traveled south from Fabricus to this pair and extend that distance even further south. Seen on the limb is crater Biela. If conditions are stable, you might pick up a tiny black point in Beila’s west wall, Biela C.

Before we retire to the shadows tonight, let’s study the small, open cluster NGC 225, located a finger-width northwest of Gamma Cassiopeiae (RA 00 43 42 Dec +61 47 00). This 7th magnitude collection has been described by some as looking like a sailboat. A fascinating name might be the ‘‘Metamorphosis Cluster,’’ since the southwestern region of the cluster looks like a butterfly asterism and, to the northeast is the caterpillar-like asterism. Although just barely detectable as an unresolved patch through binoculars on a dark night, tonight’s Moon means that magnification is needed just to make out its half-dozen brighter 9th magnitude members. Modest scopes should reveal two dozen stars to magnitude 12.

Sunday, November 22, 2009 – On the lunar surface tonight, the three rings of Theophilus, Cyrillus, and Catharina will emerge, but tonight let’s power up on Theophilus and see what we can find! The area just northeast of Theophilus—where Mare Tranquillitatis and Mare Nectaris join—is called Sinus Asperitatis.

Toward its center, you will see the remains of a once grand (nameless) crater holding the younger, sharper Torricelli in its center. Dropping back to Theophilus, just outside of its east wall, you will also find a young crater, Madler. As you head east across the northern shore of Mare Nectaris, look carefully for two partial rings. The northernmost is so eroded that it never received a name, while a slight, faint horseshoe marks all that remains of Daguerre.

Tonight let’s test our starhopping and observing talents by starting first with a beautiful double – Gamma Arietis. Now look about a fist-width east-southeast for dim little Pi. When you have Pi centered, move about half a degree southwest for an alternative catalog study—DoDz 1.

Although you might find this sparkling double handful of stars of little interest, think twice before you hop on. Although DoDz studies are far more scattered and less populous than most galactic clusters, it doesn’t make them less interesting. What you are looking at are basically the fossils of once active and more concentrated regions of stars. As the cluster has matured, the lower mass members have been stripped away and joined the general population. Known as a ‘‘dissolving cluster,’’ DoDz 1 is all that’s left of a far grander collection. Very ancient. . .yet still very beautiful!

Enjoy your celestial adventures!

This week’s awesome images are (in order of appearance): Edwin Hubble (widely used public image), Delta Cephei (credit—Palomar Observatory, courtesy of Caltech), Steinheil and Watt at limb (credit—Alan Chu), NGC 225 (credit—Palomar Observatory, courtesy of Caltech), Theophilus, Cyrillus, and Catharina (credit—Alan Chu) and Dolidze-Dzimselejsvili 1 (credit—Palomar Observatory, courtesy of Caltech). We thank you so much!

November 19, 2009December 24, 2015 by John Carl Villanueva

How Many Continents Are There?

[/caption]Not everyone on this planet is in agreement as with regards to the total number of continents. So how many continents are there then, according to the disagreeing parties?

Well, in Russia, Eastern Europe and Japan, the people there consider the continents of Europe and Asia as one, known as Eurasia. In other places in the world, North and South America are combined as one American continent while separating Europe and Asia instead. Thus, according to these two views, there should only be 6 continents.

There are even geographical views that prefer the presence of both a Eurasian as well as one American continent. These geographers therefore contend that there should only be 5 continents.

And if you thought that would be the lowest number, think again. There are others still who are more comfortable with a 4-continent view.

These people argue that, since Europe and Asia are actually part of one great land mass and that Asia and Africa are actually joined by an isthmus (Isthmus of Suez), as are the two Americas (being joined by the Isthmus of Panama), then there should be an Afro-Eurasian continent in addition to one American continent, Antarctica, and Australia.

But how many continents are there according to the more widely accepted view? In the most widely accepted view, there are 7 continents all in all: Asia, Africa, Europe, North America, South America, Antarctica, and Australia.

This model is preferred by the Chinese and majority of the English-speaking countries.

The final verdict as to how many continents are there might lean more on the larger numbers once the effects of global warming kick in. Once sea water levels rise, the separation between the two Americas as well as that between Africa and Asia will be more noticeable. Only the combined Europe and Asia model (a.k.a. 6-continent model) and the 7-continent model would remain.

Hundreds of millions of years from now, we really don’t know how many continents there would be. According to the continental drift theory, moving tectonic plates may rearrange the pieces of the puzzle that are the Earth’s continents.

What used to be one super continent, known as Pangaea has now been broken into 4, 5, 6, or 7 continents – depending on which side you’re more comfortable with. Therefore, its plausible, the Earth being round and all, that some of these continents will later on combine after drifting away for some time.

You can read more about plate tectonics here in Universe Today. Here are the links:

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

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

Sources:
Wikipedia
National Geographic

November 18, 2009December 24, 2015 by John Carl Villanueva

How Does Geothermal Energy Work

In order to understand why geothermal energy is considered an environment friendly alternative to fossil fuel, you must first be familiar with the basic workings of this technology. So how does geothermal energy work?

First of all, geothermal energy can be used in a variety of ways. There are those who utilize the heat directly for home heating (and even cooling) systems. Others use them in greenhouses, fish farms, and spas. Of course, I haven’t forgotten its most celebrated application – to produce electricity.

Thus, in answering the question, “How does geothermal energy work?”, one must first specify the specific application of the energy.

For those applications which utilize geothermal energy directly like those in fish farms, spas, and greenhouses, hot spring water is simply tapped from underneath the ground surface and redirected into these facilities.

The hot water may get its heat from magma that is able to creep upward and heat its surroundings, including the groundwater there. Magma doesn’t have to contribute heat directly though, as this melted mantle material can be found very deep underground and hence difficult to gain access to.

In some cases, where magma isn’t found in the direct vicinity, you can still obtain hot water by simply drilling deep in the ground. Always remember that the deeper you drill, the hotter the temperature gets.

Geothermal energy used to power household room heaters are extracted from the ground (not through water). During winter, ground underneath the surface is warmer than the temperature above. Heat is then extracted by using geothermal heat pumps. A typical geothermal heat pump extracts heat through a series of pipes containing either circulating water or an antifreeze solution, just like a refrigerator or an air conditioning unit.

Now for the last application mentioned earlier. How does geothermal energy work in the case of geothermal power plants?

Just like most power plants (e.g. hydro and wind power), energy is converted to electricity through the use of turbines. There are three ways of doing this.

One method directs hot steam drawn from underground into the turbine. Another draws extremely hot water from underneath, flashes it into steam, which is then directed to the turbine. The third method makes use of a heat exchanger to transfer heat from hot water drawn from underground unto a fluid (isobutane is commonly used) that is directed to the turbine.

In all three methods, the turbine is responsible for converting the kinetic energy of the directed fluid (which makes it turn) into electricity.

Universe Today has some interesting topics related to geothermal energy which you might be interested in. Here are two of them:
Geothermal Heat
Geothermal Heating

You can find more information about geothermal heat pumps from the US Department of Energy as well on the Energy Star website.

Tired eyes? Perhaps you’d like to listen to some Astronomy Cast episodes instead:
Volcanoes, Hot and Cold
Space Elevators

Sources:
http://www.ucsusa.org/clean_energy/technology_and_impacts/energy_technologies/how-geothermal-energy-works.html
http://science.howstuffworks.com/environmental/energy/geothermal-energy.htm
http://en.wikipedia.org/wiki/Geothermal_energy
http://www.eia.gov/kids/energy.cfm?page=geothermal_home-basics

November 18, 2009December 24, 2015 by John Carl Villanueva

How Do Microwaves Work

[/caption]Microwave ovens don’t operate in the same manner as conventional ovens. So how do microwaves work then? Microwave ovens take advantage of the behavior of water molecules when subjected to electromagnetic waves found in the microwave band.

To understand how this happens, we’ll have to comprehend the basic properties of water molecules and microwaves (the electromagnetic waves, not the oven).

The mickey mouse-shaped water molecule is actually a dipole. That is, one side is positively charged while the other is negative.

Microwaves used for cooking, on the other hand, are electromagnetic waves possessing frequencies around the 2.45 GHz range. Now, electromagnetic waves are waves made up of alternating electric and magnetic fields. For this discussion, we’re more concerned with the alternating electric fields because charged particles readily react when exposed to them.

That is, when a positively charged particle is exposed to an electric field, it experiences a force (due to the field) pointing in the direction of the field. By contrast, when a negatively charged particle is exposed to the same field, it experiences a force in the direction opposite to the field.

Now, since an electromagnetic wave (like the microwave) is made up of alternating electric fields, a charge exposed to it will experience forces regularly changing in direction. For water molecules, which are dipoles, the net effect would force the molecules into rotation. Again, since the fields are alternating, the rotation will change from clockwise to counterclockwise at regular time intervals.

The agitated water molecules would then possess heat energy that can rub off (much like friction) to nearby molecules. If the water molecules are well distributed in the body subjected to the microwave (like food, for example), then the entire body can heat up quickly – not to mention, uniformly.

Electromagnetic waves in the microwave range are most suitable for this purpose because the water molecules readily rotate when exposed to such frequencies.

Avoid putting in metal into the microwave oven while heating. The reason is because pointed portions of the metal can accumulate high voltages which can cause dielectric breakdown of the air inside the oven. Once this happens, some harmful gases can be produced.

Since microwave ovens normally don’t have heating elements, temperature can drop right away in the inner walls of the oven. So you’ll only need to worry about getting burned by the food and not the walls.

You can read more about electromagnetic waves here in Universe Today. Want to know about how the 25-year old mystery of X-ray emissions was solved? We’ve also written about how astronomers resolved Milky Way’s mysterious X-Ray glow

There’s more about it at NASA and Physics World. Here are a couple of sources there:
X-Ray Astronomy
X-ray Beams Thin Out

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

Source: Wikipedia

November 18, 2009April 26, 2016 by Fraser Cain

Google Satellite

If you’ve spent any time on the internet, you’ve probably had a chance to use either Google Earth or Google Maps. Both of these tools allow you to see a satellite view of the Earth, and zoom right in to see your home from space. But is there a Google satellite to take these photographs?

Google doesn’t actually have a satellite of their own. Instead, they use images from a variety of sources and store them on their servers. These images come from NASA satellites, USGS aerial surveys, and satellite photos from commercial operators. Google has an exclusive contract with a company called GeoEye, which recently launched their GeoEye-1 satellite. This commercial satellite blasted off on September 6, 2008, and is capable of resolving images on the Earth down to a size of 0.41 meters.

So how can you use these images? The easiest tool to use is Google Maps. This is a web-based tool that lets you browse around satellite photos of the Earth. You can zoom in and out, and type in a specific address anywhere on Earth to go right there. It also has driving directions, and all kinds of features that you can turn on and off to give you more information – like local sightseeing highlights.

The other tool that Google has created is called Google Earth. Unlike Google Maps, you actually need to download Google Earth to your local computer; PC, Mac, Linux, and even on your iPhone. Once you have the application installed, you see a 3-D version of the Earth that you can spin around, zoom in and out. You can zero in to any spot on Earth and see the highest resolution images they have available. There’s also a big community of developers who have created additional views that you can install. This lets you see additional photographs, contour maps, etc.

We have written many articles about Google satellite views. Here’s an article about how Google’s satellite had a bird’s eye view of the Obama Inauguration, and here’s a tool for Google Earth that lets you track satellite debris.

We’ve also recorded several episodes of Astronomy Cast about satellites. Listen here, Episode 100: Rockets.