Astronomy Archives

February 26, 2010December 24, 2015 by Jean Tate

What is Space?

First, some simple answers: space is everything in the universe beyond the top of the Earth’s atmosphere – the Moon, where the GPS satellites orbit, Mars, other stars, the Milky Way, black holes, and distant quasars. Space also means what’s between planets, moons, stars, etc – it’s the near-vacuum otherwise known as the interplanetary medium, the interstellar medium, the inter-galactic medium, the intra-cluster medium, etc; in other words, it’s very low density gas or plasma (‘space physics’ is, in fact, just a branch of plasma physics!).

But you really want to know what space is, don’t you? You’re asking about the thing that’s like time, or mass.

And one simple, but profound, answer to the question “What is space?” is “that which you measure with a ruler”. And why is this a profound answer? Because thinking about it lead Einstein to develop first the theory of special relativity, and then the theory of general relativity. And those theories overthrew an idea that was built into physics since before the time of Newton (and built into philosophy too); namely, the idea of absolute space (and time). It turns out that space isn’t something absolute, something you could, in principle, measure with lots of rulers (and lots of time), and which everyone else who did the same thing would agree with you on.

Space, in the best theory of physics on this topic we have today – Einstein’s theory of general relativity (GR) – is a component of space-time, which can be described very well using the math in GR, but which is difficult to envision with our naïve intuitions. In other words, “What is space?” is a question I can’t really answer, in the short space I have in this Guide to Space article.

More reading: What is space? (ESA), What is space? (National Research Council of Canada), Ned Wright’s Cosmology Tutorial, and Sean Carroll’s Cosmology Primer pretty much cover this vast topic, from kids’ to physics undergrad’ level.

It’s hard to know just what Universe Today articles to recommend, because there are so many! Space Elevator? Build it on the Moon First illustrates one meaning of the word ‘space’; for meanings closer to what I’ve covered here, try New Way to Measure Curvature of Space Could Unite Gravity Theory, and Einstein’s General Relativity Tested Again, Much More Stringently.

Astronomy Cast episodes Einstein’s Theory of Special Relativity, Einstein’s Theory of General Relativity, Large Scale Structure of the Universe, and Coordinate Systems, are all good, covering as they do different ways to answer the question “What is space?”

Source: ESA

February 25, 2010December 24, 2015 by Jean Tate

This Week’s astro-ph Preprints: Jean Tate’s Best Pick

Examples of ring objects (Mizuno et al./Spitzer)

It goes by the super-catchy (not!) title “A Catalog of MIPSGAL Disk and Ring Sources”. I chose it, over 213 competitors, because it’s pure astronomy, and because it’s something you don’t need a PhD to be able to do, or even a BSc.

Oh, and also because Don Mizuno and co-authors may have found two, quite local, spiral galaxies that no one has ever seen before!

Some quick background: arXiv has been going for several years now, and provides preprints, on the web, of papers “in the fields of physics, mathematics, non-linear science, computer science, quantitative biology and statistics”. It’s owned, operated and funded by Cornell University. astro-ph is the collection of preprints classified as astro physics; the “recent” category in astro-ph is the new preprints submitted in the last week.

When I have any, one of my favorite spare-time activities is browsing astro-ph (Hey, I did say, in my profile, that I am hooked on astronomy!)

Briefly, what Mizuno and his co-authors did was get hold of some of the images from Spitzer (something that anyone can do, provided their internet connection has enough bandwidth), and eyeball them, looking for things which look like disks and rings. Having found over 400 of them, they did what the human brain does superbly well: they grouped them by similarity of appearance, and gave the groups names. They then checked out other images – from different parts of Spitzer’s archive, and from IRAS – and checked to see how many had already been cataloged.

And what did they find? Well, first, that most of the objects they found had not been cataloged before, and certainly not given definite classifications! Many, perhaps most, of the new objects are planetary nebulae, and their findings may help address a long-standing puzzle in this part of astronomy.

MGE314.2378+00.9793 (Mizuno et al./Spitzer)

MGE351.2381-00.0145 (Mizuno et al./Spitzer)

But they also may have found two local spiral galaxies, which had not been noticed before because they are obscured by the gas-and-dust clouds in the Milky Way plane. How cool is that!

Here’s the ‘credits’ section of the preprint: “This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA in part through an award issued by JPL/Caltech. This research made use of the SIMBAD database and the Vizier catalog access tool, operated by the Centre de Donnees Astronomique de Strasbourg. This research has also made use of NASA’s Astrophysics Data System Bibliographic Services.”

And here’s the preprint itself: arXiv:1002.4221 A Catalog of MIPSGAL Disk and Ring Sources; D.R. Mizuno(1), K. E. Kraemer(2), N. Flagey(3), N. Billot(4), S. Shenoy(5), R. Paladini(3), E. Ryan(6), A. Noriega-Crespo(3), S. J. Carey(3). ((1) Institute for Scientific Research, (2) Air Force Research Laboratory, (3) Spitzer Science Center, (4) NASA Herschel Science Center, (5) Ames Research Center, (6) University of Minnesota)

PS, going over the Astronomy Cast episode How to be Taken Seriously by Scientists is what motivated me to pick this preprint (however, I must tell you, in all honesty, that there are at least ten other preprints that are equally pickable).

February 25, 2010December 24, 2015 by Jean Tate

Ripped to Shreds, Exoplanet Suffers Painful Death

Illustration of WASP-12b in orbit about its host star (Credit: ESA/C Carreau)

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WASP-12b, discovered in 2008, is a real outlier among the 400 or so exoplanets discovered to date. Not that it’s particularly massive (it’s a gas giant, not unlike Jupiter), nor that its homesun (host star) is particularly unusual (it’s rather similar to our own Sun), but it orbits very close to its homesun, and is considerably larger than any other gas giant discovered to date.

Results from recent research explain why WASP-12b is so unusual; we’re watching it die a painful death at the hands of its homesun, which is snacking on it.

“This is the first time that astronomers are witnessing the ongoing disruption and death march of a planet,” says UC Santa Cruz professor Douglas N.C. Lin. Lin is a co-author of the new study and the founding director of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University, which was deeply involved with the research.

The research was led by Shu-lin Li of the National Astronomical Observatories of China. A graduate of KIAA, Li and a research team analyzed observational data on the planet to show how the gravity of its parent star is both inflating its size and spurring its rapid dissolution.

WASP-12b, like most known exoplanets discovered to date, is large and gaseous, resembling Jupiter and Saturn; however, unlike Jupiter, Saturn, or most other exoplanets, it orbits its homesun at extremely close range – 75 times closer than the Earth is to the Sun, or just over 1.5 million km. It is also larger than astrophysical models predict. Its mass is estimated to be almost 50% larger than Jupiter’s and it is 80% larger, giving it six times Jupiter’s volume. It is also unusually toasty, with a daytime temperature of more than 2500° C.

Some mechanism must be responsible for expanding this planet to such an unexpected size, say the researchers. They have focused their analysis on tidal forces, which they say are strong enough to produce the effects observed on WASP-12b.

On Earth, tidal forces between the Earth and the Moon cause local sea levels rise and fall, modestly, twice a day. WASP-12b, however, is so close to its homesun that the gravitational forces are enormous. The tremendous tidal forces acting on the planet completely change the shape of the planet into something similar to that of a rugby or American football.

These tides not only distort the shape of WASP-12b. By continuously deforming the planet, they also create friction in its interior. The friction produces heat, which causes the planet to expand. “This is the first time that there is direct evidence that internal heating (or ‘tidal heating’) is responsible for puffing up the planet to its current size,” says Lin.

Huge as it is, WASP-12b faces an early demise, say the researchers. In fact, its size is part of its problem. It has ballooned to such a point that it cannot retain its mass against the pull of its homesun’s gravity. As the study’s lead author Li explains, “WASP-12b is losing its mass to the host star at a tremendous rate of six billion metric tons each second. At this rate, the planet will be completely destroyed by its host star in about ten million years. This may sound like a long time, but for astronomers it’s nothing. This planet will live less than 500 times less than the current age of the Earth.”

The WASP-12 system (Courtesy: KIAA/Graphic: Neil Miller)

About this image: The massive gas giant WASP-12b is shown in purple with the transparent region representing its atmosphere. The gas giant planet’s orbit is somewhat non-circular. This indicates that there is probably an unseen lower mass planet in the system, shown in brown, that is perturbing the larger planet’s orbit. Mass from the gas giant’s atmosphere is pulled off and forms a disk around the star, shown in red.

The material that is stripped off WASP-12b does not fall directly onto the parent star; instead it forms a disk around the star and slowly spirals inwards. A careful analysis of the orbital motion of WASP-12b suggests circumstantial evidence of the gravitational force of a second, lower-mass planet in the disk. This planet is most likely a massive version of the Earth – a so-called “super-Earth.”

The disk of planetary material and the embedded super-Earth should be detectable with currently available telescope facilities. Their properties can be used to further constrain the history and fate of the mysterious planet WASP-12b.

In addition to KIAA, support for the WASP-12b research came from NASA, the Jet Propulsion Laboratory, and the National Science Foundation. Along with Li and Lin, co-authors include UC Santa Cruz professor Jonathan Fortney and Neil Miller, a graduate student at the university.

Source: KIAA; the paper published in the February 25 issue of Nature is “WASP-12b as a prolate, inflated and disrupting planet from tidal dissipation” (arXiv:1002.4608 is the preprint).

February 24, 2010December 24, 2015 by Jean Tate

Radio Waves

The Parkes Radio Antenna. Credit: R. Hollow, CSIRO

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Radio waves are electromagnetic waves, or electromagnetic radiation, with wavelengths of about a centimeter or longer (the boundary is rather fuzzy; microwaves and terahertz radiation are sometimes considered to be radio waves; these have wavelengths as short as a tenth of a millimeter or so). In other words, radio waves are electromagnetic radiation at the lowest energy end of the electromagnetic spectrum.

Radio waves were predicted two decades or so before they were generated and detected; in fact, the historical story is one of the great triumphs of modern science.

Many years – centuries even – of work on electrical and magnetic phenomena, by many scientists, culminated in the work of James Clerk Maxwell. In 1865 he published a set of equations which describe everything known about electricity and magnetism (electromagnetism) up till that time (the next major advance was the work of Planck and Einstein – among others – some four decades or so later, involving the discovery of photons, or quantized electromagnetic radiation). Maxwell’s equations, as they are now called, predicted that there should be a kind of wave of interacting electrical and magnetic fields, which is self-propagating, and which travels at the speed of light.

In 1887, Heinrich Hertz created radio waves in his lab, and detected them after they’d travelled a short distance … exactly as Maxwell had predicted! It wasn’t long before practical applications of this discovery were developed, leading to satellite TV, cell phones, GPS, radar, wireless home networks, and much, much, more.

For Universe Today readers, the discovery of radio waves lead to radio astronomy. Interestingly, theory again preceded observation … several scientists – Planck among them – predicted that the Sun should emit radio waves (be a source of radio waves), but the Sun’s radio emission was not detected until 1942 (by Hey, in England), nearly a decade after celestial radio waves were detected and studied, by Jansky (and Reber, among others).

Here are some other webpages, or websites, with more on radio waves: Radio Waves (NASA), How Radio Waves Are Produced (National Radio Astronomy Observatory), and Radio Waves & Electromagnetic Fields (an interactive simulation from the University of Colorado).

Universe Today stories on radio waves? Sure! Device Makes Radio Waves Travel Faster Than Light, Magnetar Crackles with Radio Waves, and All-Sky Radio Image in 60 Seconds, No Moving Parts. And that’s just a sample.

Astronomy Cast episodes covering radio waves? Sure! Radio Astronomy, and Across the Electromagnetic Spectrum are two particularly good ones.

Sources:
Wikipedia
NASA
NRAO

February 23, 2010December 24, 2015 by Tammy Plotner

Celestron NexStar 130SLT Computerized Telescope

Are you looking for a computerized telescope that’s designed for the more serious amateur astronomer? Then you need to take a look at the Celestron NexStar 130SLT Computerized Telescope. This reflector telescope is both advanced in size and in capabilities! Let’s take a look at what makes the NexStar 130 SLT tick…

Celestron NexStar 130 SLT Computerized Telescope – Optical Tube Assembly – The popularity of the Celestron NexStar 114 models inspired Celestron to go bigger and they are proud to introduce NexStar 130 SLT. The 130 mm (5.12 in) aperture size has 30% more light-gathering power than the NexStar 114 SLT telescope and 345 times more light grasp than the human eye alone. This means an outstanding limiting stellar magnitude of 13.1! With a 650 mm (25.59 in) focal length, the Celestron NexStar 130 SLT Computerized Telescope operates at a focal ratio of f/5 – giving it a total useful magnification factor of 307X. The 130mm primary mirror is crafted from the finest optical glass and precision ground to exacting tolerances – then given durable aluminum coatings for years of care-free reflective performance. It has an outstanding resolution of 0.89 arc seconds and a photographic resolution of 400 line/mm. The Celestron NexStar 130 SLT Computerized Telescope also has an upgraded 2″ rack and pinion focuser, too!

Celestron NexStar 130 SLT Computerized Telescope – Mount – Driving the Celestron NexStar 130 SLT is a single arm fork mount with nine slew speeds: 4°/sec, 2°/sec, 1°/sec, .5°/sec, 32x, 16x, 8x, 4x, 2x. It works in both hemispheres and tracks in Sidereal, Solar and Lunar rates. A clamshell scope ring with a captive bolt holds the optical tube assembly securely and attaches to the sturdy stainless steel tripod via a captive, ergonomic center bolt. No worries about anything getting tangled during use… the battery compartment is internalized so there’s no “cord wrap” issues and it even includes an auxiliary port for additional accessories such as GPS. There’s no wingnuts to get lost in the dark on the tripod either… Just clamp the tublar legs at the desired height and add the accessory tray for additional stability. Now that’s a quick and easy no tool setup!

Celestron NexStar 130 SLT Computerized Telescope – NexStar Hand Control – The brains behind the brawn is the patented Celestron NexStar system. The SkyAlign feature allows you to align on any three bright celestial objects, making for a fast and easy alignment process. Simply input the date, time and your location (the CPC models have built-in GPS that does this for you) and then align the telescope to three bright stars of your choosing. You do not need to know the names of the stars — you could even pick the moon or bright planets! The NexStar Computer telescope system will automatically figure out which stars were chosen and then align the telescope. There is no need to point the telescope North or to level the optical tube – the initial position of the telescope is irrelevant. The computerized hand control gives you the ability to automatically slew to any of its 4,000+ objects, including over 600 galaxies, 300 clusters and dozens of beautiful binary stars. But it doesn’t stop there… The Celestron NexStar 130 SLT Computerized Telescope can also locate comets, geostationary satellites and asteroids, too! The flash upgradeable hand control software and motor control units are always ready for downloading product updates over the Internet and adding an optional GPS unit makes things even easier. The NexStar 130SLT includes NSOL telescope control software for basic control of your telescope via computer (with optional RS-232 cable) and it’s compatible with optional NexRemote telescope control software, for advanced control of your telescope via computer.

Celestron NexStar 130 SLT Computerized Telescope – Accessories – The Celestron NexStar 130 SLT Computerized Telescope is ready to go just as soon as you are. The package includes a StarPointer red dot reflex finderscope and two eyepieces: a 25 mm (0.98 in) that provides 26X magnification and a 9 mm (0.35 in) eyepiece that delivers 72X. You won’t be left “in the dark” either. The package also includes “The Sky” Level 1 planetarium software and the NexStar Observers List (v2.6.4c).

Weighing in at right around 18 lb (8.16 kg), Celestron’s most affordable NexStar 130 SLT Computerized Telescope turns starry nights into space odysseys. Set it up in your own backyard or travel to a dark sky location with ease. You can see breathtaking views of the lunar landscape, Venus and its phases, Mars resolved as an orange disc, Jupiter and its 4 moons, Saturn resolved as a disc, with its rings plainly visible at medium and high magnification. Add to that beautiful star clusters and distant galaxies and you have a tool you’ll use for many, many years to come!

February 23, 2010December 24, 2015 by Jean Tate

Proton Mass

The mass of the proton, proton mass, is 1.672 621 637(83) x 10 ^-27 kg, or 938.272013(23) MeV/c², or 1.007 276 466 77(10) u (that’s unified atomic mass units).

The most accurate measurements of the mass of the proton come from experiments involving Penning traps, which are used to study the properties of stable charged particles. Basically, the particle under study is confined by a combination of magnetic and electric fields in an evacuated chamber, and its velocity reduced by a variety of techniques, such as laser cooling. Once trapped, the mass-to-charge ratio of a proton, deuteron (nucleus of a deuterium atom), singly charged hydrogen molecule, etc can be measured to high precision, and from these the mass of the proton estimated.

It would be nice if the experimentally observed mass of a proton were the same as that derived from theory. But how to work out what the mass of a proton should be, from theory?

The theory is quantum chromodynamics, or QCD for short, and is the strong force counterpart to quantum electrodynamics (QED). As the proton is made up of three quarks – two up and one down – its mass is the mass of those quarks and the mass of binding energy. This is a very difficult calculation to perform, in part because there are so many ways the quarks and gluons in a proton interact, but published results agree with experiment to within a percent or two.

More fundamentally, the proton has mass because of the Higgs boson … at least, it does according to the highly successful Standard Model of particle physics. Only trouble is, the Higgs boson has yet to be detected (the Large Hadron Collider was built with finding the Higgs boson as a key objective!).

Want to know the “official” value? Check out CODATA. And how does the proton mass compare with the mass of the anti-proton? Click here to find out! And how to determine the proton mass from first (theoretical) principles? This article from CNRS explains how.

More to explore, with Universe Today stories: New Estimate for the Mass of the Higgs Boson, Are the Laws of Nature the Same Everywhere in the Universe?, and Forget Neutron Stars, Quark Stars Might be the Densest Bodies in the Universe are three good ones to get you started.

Astronomy Cast episodes The Strong and Weak Nuclear Forces, The Large Hadron Collider and the Search for the Higgs Boson, and Inside the Atom will give you more insight into proton mass; check them out!

Sources:
Newton Ask a Scientist
Wikipedia

February 23, 2010December 24, 2015 by Fraser Cain

Pictures of Moons

Here are some pictures of moons, from across the Solar System. You can make any of these images into your computer desktop wallpaper. Just click on an image to enlarge it. Then right-click and choose “Set as Desktop Background”.

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Here’s an image of Mars’ moon Phobos, taken by the Mars Reconnaissance Orbiter. The orbit of Phobos is slowly spiraling inward, and astronomers think it will collide with Mars in the next few million years.

Here’s a global view of Jupiter’s moon Io captured by NASA’s Galileo spacecraft. Because of the powerful tidal gravitational forces from Jupiter, Io is extremely volcanic, and can blast lava hundreds of kilometers into space.

Here’s an image of Saturn’s moon Mimas with Saturn as a backdrop. This photo was taken by NASA’s Cassini spacecraft, currently orbiting around Saturn. Mimas has a huge crater from an asteroid impact that almost destroyed it millions of years ago; this makes it look like the Death Star.

Here’s a montage of Neptune and Triton captured by NASA’s Voyager 2 spacecraft, which flew past the planet in 1989. Voyager 2 was the first and still only spacecraft to ever reach Uranus and Neptune, and have given us the only close up pictures taken of the planets.

This is a familiar moon… it’s the Moon, seen from the International Space Station. You can see how the Earth’s tenuous atmosphere transitions from the planet into the blackness of space.

We’ve written many articles about moons for Universe Today. Here’s an article about how many moons Earth has, and here’s an article about how many moons there are in the Solar System.

If you’d like more info on the Solar System, check out NASA’s Solar System exploration page, and here’s a link to NASA’s Solar System Simulator.

We’ve also recorded a series of episodes of Astronomy Cast about every planet in the Solar System. Start here, Episode 49: Mercury.

February 23, 2010December 24, 2015 by Jean Tate

Better Late Than Never: Dwarf Galaxies Finally Come Together

Hickson 31 (Credit: NASA, ESA, and S. Gallagher (The University of Western Ontario), and J. English (University of Manitoba))

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Have you heard of ‘living fossils’? The coelacanth, the ginko tree, the platypus, and several others are species alive today which seem to be the same as those found as fossils, in rocks up to hundreds of millions of years old.

Now combined results from the Hubble Space Telescope, Spitzer, Galaxy Evolution Explorer (GALEX), and Swift show that there are ‘living galaxy fossils’ in our own backyard!

Hubble: red, yellow-green, and blue; Spitzer: orange; GALEX: purple

Hickson Compact Group 31 is one of 100 compact galaxy groups catalogued by Canadian astronomer Paul Hickson; the recent study of them – led by Sarah Gallagher of The University of Western Ontario in London, Ontario – shows that the four dwarf galaxies in it are in the process of coming together (or ‘merging’ as astronomers say).

Such encounters between dwarf galaxies are normally seen billions of light-years away and therefore occurred billions of years ago. But these galaxies are relatively nearby, only 166 million light-years away.

New images of this foursome by NASA’s Hubble Space Telescope offer a window into the universe’s formative years when the buildup of large galaxies from smaller building blocks was common.

Astronomers have known for decades that these dwarf galaxies are gravitationally tugging on each other. Their classical spiral shapes have been stretched like taffy, pulling out long streamers of gas and dust. The brightest object in the Hubble image is actually two colliding galaxies. The entire system is aglow with a firestorm of star birth, triggered when hydrogen gas is compressed by the close encounters between the galaxies and collapses to form stars.

The Hubble observations have added important clues to the story of this interacting group, allowing astronomers to determine when the encounter began and to predict a future merger.

“We found the oldest stars in a few ancient globular star clusters that date back to about 10 billion years ago. Therefore, we know the system has been around for a while,” says Gallagher; “most other dwarf galaxies like these interacted billions of years ago, but these galaxies are just coming together for the first time. This encounter has been going on for at most a few hundred million years, the blink of an eye in cosmic history. It is an extremely rare local example of what we think was a quite common event in the distant universe.”

In other words, a living fossil.

Everywhere the astronomers looked in this group they found batches of infant star clusters and regions brimming with star birth. The entire system is rich in hydrogen gas, the stuff of which stars are made. Gallagher and her team used Hubble’s Advanced Camera for Surveys to resolve the youngest and brightest of those clusters, which allowed them to calculate the clusters’ ages, trace the star-formation history, and determine that the galaxies are undergoing the final stages of galaxy assembly.

The analysis was bolstered by infrared data from NASA’s Spitzer Space Telescope and ultraviolet observations from the Galaxy Evolution Explorer (GALEX) and NASA’s Swift satellite. Those data helped the astronomers measure the total amount of star formation in the system. “Hubble has the sharpness to resolve individual star clusters, which allowed us to age-date the clusters,” Gallagher adds.

Hubble reveals that the brightest clusters, hefty groups each holding at least 100,000 stars, are less than 10 million years old. The stars are feeding off of plenty of gas. A measurement of the gas content shows that very little has been used up – further proof that the “galactic fireworks” seen in the images are a recent event. The group has about five times as much hydrogen gas as our Milky Way Galaxy.

“This is a clear example of a group of galaxies on their way toward a merger because there is so much gas that is going to mix everything up,” Gallagher says. “The galaxies are relatively small, comparable in size to the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Their velocities, measured from previous studies, show that they are moving very slowly relative to each other, just 134,000 miles an hour (60 kilometers a second). So it’s hard to imagine how this system wouldn’t wind up as a single elliptical galaxy in another billion years.”

Adds team member Pat Durrell of Youngstown State University: “The four small galaxies are extremely close together, within 75,000 light-years of each other – we could fit them all within our Milky Way.”

Why did the galaxies wait so long to interact? Perhaps, says Gallagher, because the system resides in a lower-density region of the universe, the equivalent of a rural village. Getting together took billions of years longer than it did for galaxies in denser areas.

Source: HubbleSite News Release. Gallagher et al.’s results appear in the February issue of The Astronomical Journal (the preprint is arXiv:1002.3323)

February 22, 2010December 24, 2015 by Jerry Coffey

Atom Structure

[/caption]We know that atoms are parts of an element that can not naturally be broken down any further. What is the atom structure, though? The concept that atoms existed was first written about in ancient India in the 6th century B.C. The theory stayed just that, a theory, until the late 19th century. As microscopes and spectrometers developed, scientists were better able to develop their theories and finally observe the small scale structure of elements.

Atoms are made up of three particles: protons, electrons, and neutrons. Electrons are the smallest and lightest of the the three particles and they have a negative charge. The protons are much heavier and larger than electrons. Protons have a positive electrical charge. Neutrons are as large and massive as protons, but do not have an electrical charge at all. Every atom contains these particles in varying numbers. To understand exactly how small an atom is, you have to know that a single hydrogen atom is 5 x 10^-8mm in diameter. It would take at least 60 million hydrogen atoms to fill the space of any one of the letters on this page.

The simplest atom is that of hydrogen: 1 electron and one proton. In every stable, neutrally charged atom there is the exact same number of protons as electrons. These particles work together like two magnets with the opposite electrical charges attracting each other. The reason that they do not crash together is that the electron is constantly revolving around the nucleus(usually a proton/neutron combination, but hydrogen, uniquely, does not contain any neutrons). The centrifugal force of the electron keeps it in place at a constant distance from the nucleus. Actually, representing the electron as spinning around the nucleus is somewhat misleading. Electrons act like waves. That is how they are seen on a spectrometer. It is just easier to think of them as spinning around.

Atoms can have an electrical charge, positive or negative. This happens when an atom gains or loses electrons. The number of protons never changes in an atom. More electrons means a negative charge and fewer means a positive charge. Once an atom has an electrical charge it is called an ion. In an ion the atomic number and atomic mass do not change from the original. If an atom were to gain or lose neutrons it becomes an isotope. Remember the hydrogen atom I mentioned earlier. It did not have a neutron attached to its proton. If it gains a neutron it become an isotope called deuterium. Since the atomic mass is the total of the number of protons and neutrons, an isotope would have a different atomic mass, but the same atomic number as the original atom.

Alright, that is a very basic rendition of atom structure. The University of Colorado has an interesting website to help you understand more complex versions of atoms. Here on Universe Today we have a great article about the many theorized models of the atom. We discussed ions. Astronomy Cast offers a good episode about interstellar travel using ion propulsion.

Sources:
Wikipedia
GSU Hyperphysics

February 22, 2010December 24, 2015 by Abby Cessna

Naiad

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Naiad is one of the 13 moons of Neptune. Neptune was not discovered until 1989 through studying photos taken by the Voyager 2 probe. Thus, the Voyager Science Team is credited with its discovery. It was the last moon discovered by the probe, which helped scientists find five moons altogether. The last five new moons were discovered in the first decade of the 21st century.

The satellite was given its official name on September 16, 1991. At first the satellite was designated S/1989 N 6. Neptune’s moons are named after figures from mythology that have to do with the Roman god Neptune – or its Greek equivalent Poseidon – or the oceans. The irregular satellites of Neptune are named after the Nereids, which are the daughters of Nereus and Doris, who are Neptune’s attendants in Roman mythology. Naiad was named after a type of nymph in Greek mythology that presided over brooks, streams, wells, springs – all fresh water things.

Naiad is the closest satellite to the planet Neptune. It orbits about 48,230kilometers from the top of the planet’s atmosphere. Naiad is a very small satellite with a diameter of only approximately 58 kilometers. That is about one-sixtieth the size of the Earth’s Moon. Naiad’s mass is so small that it is only 0.00001% of the Moon’s mass. It takes Naiad less than one day – seven hours and six minutes to be precise – to orbit Neptune because of its proximity to its planet. With a decaying orbit, the satellite may crash into Neptune or be ripped apart and become part of one of its planetary rings. This may happen soon.

Naiad is an irregularly shaped satellite, which some have compared to a potato. In one of the pictures Voyager 2 took of it, the moon appears to be elongated because of smearing in the picture. Astronomers believe that the moon is made up of fragments from Neptune’s original satellites, some of which were destroyed when Neptune’s gravity captured Triton as a satellite. They do not think the moon has changed at all geologically since it was formed.

After the Voyager 2 probe passed by Neptune, the planet and its satellites have been studied by many observatories as well as the Hubble Space Telescope and the Keck telescope. Although scientists have been trying to observe Naiad and some of the other smaller irregular moons, scientists still do not know very much about the satellite. This is especially true because Naiad and similar satellites are so small.

Universe Today has articles on Neptune’s moons and moons of Neptune.

You should also check out Neptune’s moon Naiad and Naiad.

Astronomy Cast has an episode on Neptune you will want to see.

Source: NASA