50″ Dedication: World’s Largest Privately Owned Research Telescope October 20, 2014Posted by jcconwell in Astronomy, Observatory, telescopes.
Tags: ARI, Astronomical Research Institute, Eastern Illinois University, EIU, Observatory
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On a nightly basis, Holmes quietly monitors the universe. He does so from his rural Westfield home, located about 10 miles east of Charleston, and he stills uses telescopes – although they’ve graduated greatly in size. In fact, Holmes recently completed the construction and installation of a 50-inch (size of the mirror) telescope, making him the proud owner of the largest privately owned telescope in the world. It is the fourth in a collection that also includes a 24-inch, a 30-inch and a 32-inch telescope – each of which has its own outbuilding to keep it safe from the elements.
“The buildings are about 10-feet wide, with roofs that slide straight back,” Dr. Steve Daniels, EIU Physics Chair said. “Bob did his own design.”“There’s a microwave link between the observatory on Bob’s property and EIU,” he continued. “It’s Web-based, made possible as a result of a very strong collaborative effort.”Holmes’ connection with Eastern goes even deeper.“As an adjunct professor, he hosts our astronomy classes; they go out to his property a couple of times a year, at least,” Daniels said. “And he works closely with Jim Conwell, the physics professor who built Eastern’s own observatory.“Students are an integral part of Bob’s work,” he added. “And not just with students at EIU. Through his work, Bob reaches about 300 schools in 40 countries, working with students to analyze the multitude of data that he collects. He helps researchers – both young and old – by making his equipment available to Skynet, an internet-based telescope-sharing network.
“He generates an enormous database of photographs that he collects almost every night, and then uploads it to the Web for others to use. He holds workshops to train teachers to analyze astronomical data, including how to identify asteroids in a series of photographs, and encourages them to pass this knowledge along to their own students,” Daniels said.
Of course, Holmes does continue to spend many of his nights in solitude, gazing up into the skies. And he continues to break records for discovering and tracking Near Earth Objects. In fact, despite the many major observatories, Holmes is responsible for nearly half of all NEO measurements made in 2011.
“In other words, his observatory is responsible for more NEO data that anyplace else in the world,” Daniels said. “From his observatory in Westfield, Bob Holmes stands guard over our world.
Excerpts were taken from the full article that can be seen at EIU.
Haunted Observatory TONIGHT! October 25, 2013Posted by jcconwell in Astronomy.
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Come see the real mad scientists at the haunted observatory tonight starting at 8:00 PM. The observatory is ringed with Jack o lanterns and my minions (er… students) will be there to answer all your questions and experiment on you.
Two Year Project Done August 16, 2013Posted by jcconwell in Astronomy, Observatory, telescopes.
Tags: ARI, Eastern Illinois University, EIU, microwave, Observatory, telescope
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This week we have completed a two year long project to connect the telescopes at the Astronomical Research Institute (ARI) to the high speed internet access at EIU. This was done with a direct, line of sight, microwave link over the 12 miles separating ARI and the EIU campus. This increases the bandwidth to upload images every night by a factor of at least 15.
The new wide-field camera (32 megabytes per image) took 10-15 minutes per image to up load, under the old connection. At times it wasn’t even possible as the uploader gave up and stopped running. It takes about 30-40 seconds now per image with zero failure rate. The 2 meg images on the other cameras are less than 2-3 seconds.
Just two telescopes took 12-16 hrs for upload with just the 2 meg images with the old internet. ARI never even tried the new camera on the old internet except to test the time it took. Now all three scopes can be uploaded in about 90 minutes. That’s about 2,500 images or 6 gigs of data. We are typically done by 6am!
Some day the 50 inch will be working and adding another 1.5 gigs of data per night with the large format Apogee camera. Until then enjoy a look at one of the first test pictures uploaded from the wide field camera on the 30″ telescope. the galaxy M33
Thank you to the Haunted Observatory Crew October 29, 2012Posted by jcconwell in Astronomy, Observatory.
Tags: Eastern Illinois University, EIU, halloween, Jack o'Lanterns, Observatory, pumpkin
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This last Friday we had our annual Halloween open house at the observatory. Thanks to all the pumpkin carvers and heroes who made it all possible!
And some of our favorite heroes of the night
CURIOSITY TOUCHDOWN 10:31PM PDT (12:31AM CDT) TONIGHT!!! August 5, 2012Posted by jcconwell in Astronomy, planets, Space Craft.
Tags: Curiosity, Mars, planets, Solar System
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TONIGHT the largest rover ever to land on a planet will enter Mar’s astmosphere! Curiosity is over 5 times bigger than the previous Mar’s rover. To get the details of what is refereed to the “7 minutes of terror” , which is what the scientists call the time it takes to enter the Martian atmosphere and land, click on the NASA video below. Since Mars is 154,000,000 miles away it takes a light or radio signal 14 minutes to reach Earth. So the landing is totally controlled by the on-board computer reading the sensors, and then adjusting the course. For the scientists waiting on Earth who have spent a good part of a decade on this mission, it will be closer to 7+14=21 minutes of terror, before they know if it is a success or a failure.
There will be a GOOGLE+ hangout event sponsored by Universe Today at http://goo.gl/a5t4O
Spectroscopy-The Astronomers Amazing Tool! August 2, 2012Posted by dwelchscience in Astronomy, physics.
Tags: physics, spectra
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Can we really solve all the mysteries of the Universe? Well, maybe not but SPECTROSCOPY certainly holds the key to unfolding many planetary secrets! What benefit do we get from the study of spectroscopy? Basically….
Almost all knowledge of the composition of the solar system comes from spectroscopy.
Scientists are also looking at:
Nasa’s Hubble telescope, which is delving into the far reaches of the universe looking for large scale structures with a new tool, the “cosmic origins spectrograph.”
Nasa is planning to launch a telescope that will help us see beyond the Hubble’s capabilities, in order to examine Infrared light from the oldest parts of the universe.
What is SPECTROSCOPY?
Spectroscopy relates to the dispersion of an object’s light into its individual colors or energies. By analyzing the object’s light, astronomers can determine the various physical properties of that object, such as temperature, mass, luminosity and composition.
Before going further it is important to review some basics of light: What is light? How does it behave? It’s been a very long haul through time to solve these two very fundamental questions. During this century alone, with the development of quantum mechanics have we understood quantitatively how light and atoms work.
Dual nature of Light:
Light behaves like a wave. Light has a particle nature also, but for now let’s focus on the wave nature of light. Waves are disturbances that possess a height (amplitude), in which the peak is the crest and the base is the trough. When a certain number of waves pass per unit of time, such as the second, this is called frequency . The unit for frequency is nu, ν, and means cycles per second, or hertz (Hz). The characteristic speed the wave moves through a medium is the wave speed. The distance between successive waves is the wavelength, given the symbol lambda, ( λ). Often given in meters or nanometers. The diagram below demonstrations two types of waves, low and high energy:
We can think of the above wave diagram like the water in the ocean. Or, let’s direct our thoughts to waves of LIGHT. The wave speed is the speed of light ,(c) a nd different wavelengths of light manifest themselves as different colors! The energy of light wave is inversely proportional to its wavelength, or low-energy waves have long wavelengths and low frequency. High energy waves have short-wavelengths and high frequency.
The Electromagnetic Spectrum:
Physicists classify light waves by their energies or wavelengths. Below is the Electromagnetic Spectrum which gives us a chart of this. The shorter the wavelength beyond visible light the more dangerous the form of energy to organisms. The human eye can only respond to the visible light spectrum, between 700-400 nm (ROYGBBIV).
When we look at the universe in non-visible wavelengths, we can probe different kinds of physical conditions-enabling us to see new objects in space! For example, today we have high energy gamma-ray and X-ray telescopes in which we can visualize galaxies, remnants of dying stars, matter around black holes, etc. However, visible light telescopes are best to probe light produced by stars. Longer-wavelength telescopes are used to study dark, cool, obscure structures: star-forming regions, dark cold molecular clouds, and primordial radiation emitted by the formation of the Universe.
“By studying astronomical objects at different wavelengths astronomers can piece together a comprehensive picture of how the Universe works.”
Types of Spectra:
There are 2 general types of spectra: continuous and discrete. The continuous spectrum is composed of light that is a continuous range of colors (energies). With discrete spectra, the light consists of dark or bright bands of very distinct colors (energies). The discrete spectra with bright bands is referred to as emission spectra, and those with dark lines are absorption spectra.
The continuous spectra generates from dense gases or solid objects that radiate heat away due to the production of light. These objects produce light over a broad spectrum of wavelengths, therefore the spectrum appears “continuous”. Stars emit light generally in a continuous spectrum but not always. Other examples of objects emitting light: light bulbs, electric stove filaments, cooling fire embers, flames and YOU! Yes, believe it or not you are emitting a continuous spectrum but at infrared wavelengths that are not visible to your eye. Infrared (IR), would be lower energy and longer wavelengths than red light.
Light & Matter: Arapaho.nsuok.edu
Discrete spectra are the result of the atom. There are two forms of discrete spectra: emission (bright line) and absorption (dark line) spectra.
Emission Line Spectra:
Unlike the continuous spectrum which can have any energy by changing the temperature, the electron cloud surrounding the nuclei can only have very “specific, discrete packets of energy” or quanta. Each element on the periodic table has its own set of energies and most are very distinct and identifiable.
The diagram below shows a hydrogen atom dropping from the 2nd energy level to the first. As it drops it emits a wave of light, photon, with an energy equal to the difference between the second and first energy levels. This energy corresponds to a specific color or wavelength of light, therefore we see a bright line at that exact wavelength. This is an emission spectrum, see example below:
Very small changes in energy generate photons with small energies and long wavelengths, such as radio waves. Large changes in energy in an atom will result in high-energy, short-wavelength photons: UV, X-ray, and gamma rays. The diagram below shows an excited Hydrogen atom emitting a photon resulting in a bright line emission line.
Absorption Line Spectra:
What about reversing this process? What happens if we fire a photon back into a ground state atom? The atom would become excited and jump to a higher energy level. If a star with a “continuous spectrum” is shining upon an atom, the wavelengths of each energy transition would be absorbed and we would not see them. This would be a dark line absorption spectrum. The diagram below shows this process of a hydrogen atom absorbing the exact photon to produce a dark absorption line.
In the diagram below, the absorption spectrum example is from medium resolution of the Sun’s spectrum. The dark lines are called Fraunhofer lines, or solar absorption lines. These lines are a combination of lines produced as sunlight passes through the outer layers of the Sun’s atmosphere AND lines from the sunlight that goes through Earth’s atmosphere. A comparison can be made to identify & remove the Earth’s lines, therefore allowing scientists to determine the atoms and molecules coming from the Sun’s spectrum. Also observe the second diagram below for analyzing stars.
In the above diagram we see the continuous spectrum of the sun produced as its light moves outward towards us. When the light reaches the cooler chromosphere (solar atmosphere) some colors or light are absorbed. So astronomers can see an absorption spectrum due to the absorption of the chromosphere.
Spectrometer: A Powerful Applications in a Simple Device!
A spectrometer is an instrument used to measure properties of light over a certain portion of the Electromagnetic Spectrum, with a purpose of spectroscopic analysis in order to identify different materials. Usually, the variable being measured is light intensity, however, other factors could be looked at such as polarization state of light. The independent variable is the wavelength of light, or a unit inversely proportional to the photon energy or electron volts and wavenumber. A spectrometer is used to produce spectral lines and measuring their intensities and wavelengths. Spectrometer is designed to operate over a wide range of wavelengths, from gamma, x-rays, or to the far-infrared. There are several kinds of spectrometers, such as spectrographs that measure wave frequency by using photographic paper as a detector. The star spectral classification and the discovery of the main sequence, Hubble’s Law, and the Hubble sequence were all made using photographic paper. Today, detectors are electronic, such as CCD, which can be used for visible and UV light. The choice of detector depends upon the wavelength of light being analyzed.
A spectrometer consists of 3 basic parts:
1) A small telescope collects light which is focused into a thin beam by using a narrow slit and specific lenses.
2) A diffraction grating acts like a prism and a spectrum is produced from the incident light.
3) A detector, or photocell, measures the intensity of the light in various regions of the spectrum. A voltmeter can be used as a detector.
4) The detector “scans” the spectrum and intensity of each point of light is graphed. The result is shown in the graph below:
Most people have a general idea of how a telescope works, but not a spectrometer. The following diagrams below explain the basic structure of a spectrometer. There are many types, this example is one that was used at an Astronomy Space Camp for kids.
- Light beam enters the spectrometer.
- The focal point is directed to the slit, which is imaged on the detector.
- The slit is set at an angle and the area around it is silvered so that the beam not passing through the slit can be re-routed to the eyepiece for easy guiding of the telescope.
Diagram #2- this picture shows the light passing through the slit and being bounced off of a collimating mirror in order to parallelize the light before it goes to the diffraction grating.
Diagram #3- the diffraction grating disperses the parallel beams of light into its individual colors, wavelengths, and energies. Each “individual” beam coming out of the grating is bent at a different angle or wavelength. The image we see looks like a rainbow of colors.
The colored-dispersed beam of light is focused and imaged on the detector using a 35 mm camera lens. The space camp spectrometer used an eyepiece or CCD.
(All hand-drawn diagrams taken from Spectroscopy Space Camp- loke.as.arizona.edu)
So, putting all the parts together, the diagram above shows the complete Spectrometer. An important point to make concerning Spectroscopy: astronomers are not looking at ALL the light, but a certain “region” of wavelength of color. Because surface brightness is lower when taking images a bigger telescope is needed to get a good spectrum of an object in space.
The narrower the slit and farther the light is dispersed, the better the resolution. This enables astronomers to view the more subtle characteristics of the spectrum. The down side is, the spectrum becomes dimmer and more diffuse. Retaining clarity is difficult, magnifying an image usually results in a more blurred object. Therefore, high resolution spectroscopy requires a BIGGER telescope and brighter objects to view! For the dim objects in the night sky, resolution will be sacrificed.
Examples of Spectroscopy in Astronomy:
A lot of valuable information can be obtained from the use of spectroscopy in Astronomy. We can gather information about the temperature, density, composition and physical processes of objects in space.
When peering into the far reaches of space some questions that we may ask: What is it? How did it get here? What is it made of? How did the universe begin? What will happen during the object’s life cycle? Astronomers can gather valuable data using spectroscopy and other means to attempt to answer such questions.
Comets: comets are formed from materials dating back to the earliest times when our solar system was forming. The composition of these “dirty snowballs” can give us clues into our universe’s early history.
Two images taken 9 minutes apart showing the comet and mag 9 star SAO 80381 embedded in the comma. A rather noisy image with only 5 frames taken due to cloud cover, however, the spectrum is visible. Taken by 80 mm and f5 refractor.
Hale Bopp- March-April 1997: the strong background lines are from the Mercury streetlights. Authors heard that a newly discovered tail was composed of Sodium, so they set out to prove if this was correct. The slit was centered on the tail and a sodium emission line at 589 nm was the result, it was Sodium!
Star Formation in Colliding Galaxies:
When the universe was forming billions of years ago, there were intense, rapid star formation going on. This has since decreased a great deal. Astronomers know that galaxies demonstrate violent and extreme star formation. “Starburst” galaxies show up best in the Infrared and Radio wavelengths. This is because they harbor so much dust and gas that this prevents the penetration of visible light, especially in the center where star formation takes place. The above spectrum shows Infrared between 20,000-25,000 Angstroms of two starburst galaxies, most of which is H2 gas—what stars are made of! From the hydrogen emissions the molecular gas is very warm. In the top galaxy the gas is excited by shock heated gas. The bottom spectrum shows molecular H2 excited by UV light from a recently formed, young and hot star.
Quasar were discovered in the 1960’s and determined to be red-shifted due to the speeding away or expansion of quasars from us. This process is explained in the Big Bang Theory of cosmology, which states that the faster its speeding away from you the more distant it is. Quasars are the most distant astronomical bodies known to man. The diagram below is the spectrum for a Quasar, in which the most obvious emission line is Hydrogen at 1216 Angstroms. The hydrogen atom is making the transition from the first excited state to the ground state. The emission line at 1216 Angstroms is in the UV where Earth’s atmosphere is opaque, quasars are expanding very rapidly away from us so that this emission line is red-shifted into the visible light portion of the spectrum at 4,000-7,000 Angstroms.
Planetary Nebulas & Why Pollution Filters Work:
Image of M57 aka the “Ring Nebula” with spectrometer slit shown in red. This is 180 second exposure on a 10” Meade Schmidt-Cassagrain telescope. The resulting image on the spectrum shown below has an emission line at 4861 Angstroms. This comes from hot, excited atomic hydrogen. Highly – excited atoms in M57’s gaseous shell begins at energy level 4 and will probably drop to level 2, giving up energy by the difference between the two levels. The two brightest lines at 4959 and 5007 indicate that conditions in this nebula are indeed very harsh! Temperatures consist of several thousand Kelvins and very thin density (1-100 atoms/cm3). A LINE spectrum is seen, proving that planetary nebulae are hot rarified gases! This spectrum also reinforces the fact that using light-pollution filters help viewers get great contrast from reflection/emission nebulae by blocking out all wavelengths due to skyglow and allow for only the wavelengths in the range needed for viewing nebulas.
Sirius-The Dog Star:
Shown below is a ½ second exposure of Sirius centered near 4,000 Angstroms in the blue, near-UV and shows a series of deep absorption lines. Sirius’s outer atmosphere is cooler and mildly excited H atoms in the 2nd energy level are “zapped” by photons. This sends them to higher excited states. The dark absorption line in the diagram is the result of each transition upward in the H atom. The higher energy transitions on the left are the result higher energy absorption in the UV. (Balmer series).
Stars are classed by their temperatures, determined by their spectral features. Hottest stars are called O-stars, then B..A, F, G, K and lastly, M-stars. Hotter stars give off more light. Sirius is a hot A-type star with a temperature of 10,000 Kelvin. This type of star has the strongest hydrogen features due to their temperature. These hot stars ionize the hydrogen atoms that form the spectral lines!
Below is a another diagram of the classification scheme of stars, (OBAFGKM). Each category further divided into 10 subclasses. A mnemonic for remembering the sequence is: Oh Be A Fine Girl/Guy Kiss Me. Spectral type tells you about the surface temperature of a star. Notice there are few spectral lines for the hot O & B region. This indicates the simple atomic structure related to high temperature.
The appearance of stars is related more to the continuous spectrum of the inner parts of the star than the absorption at its surface. The continuous spectra for the interior of stars is described by Planck Curves shown in the two figures below. As the temperature increases, total amount of light energy (area under curve) increases also and the peak wavelength moves to a smaller more energetic wavelength.
Spectral Classification- Identifying a Star’s Lifespan
Using information obtained from Planck’s Curve and wavelength we can now determine star temperature and color in order to get an idea of a star’s approximate life expectancy. The following table lists corresponding values of color, temperature, mass and life expectancy of the stars in the OBAFGKM system.
Below are two charts, a plot of star luminosities versus stellar temperatures, is called an H-R diagram and a more detailed chart of radius, mass, luminosity, etc. Students can make comparisons of basic properties of each class type using this chart.
About 90% of all stars lie in the “main sequence” which stretches from hot, bright blue supergiants and giants through intermediate stars such as our sun to cool red dwarfs. By using spectroscopy astronomers can determine the luminosity class of a star. A valuable tool for astronomers, the spectrometer and spectrograph, that gives them insight into our distance stellar neighbors.
Students can conduct a further study by going to astro.unl.edu/naap under Spectral classification, “Practice exercises” and answer the following:
1) What are the surface temperatures and colors of O2, M3, and G2 stars? 2) What is the spectral type of a star with surface temperature of a) 10,000K and b) 5,000K? 3) What is the color of a star with spectral type A0 and surface temperature 4,000K? Answers to these can be determined by using the “sliding” star graph on the website.
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Cosmic Holes July 26, 2012Posted by hellerphysics48 in Astronomy, Black Holes, Quasars.
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We have gazed out into the sky for thousands of years, with each passing generation developing a deeper understanding how the universe functions. In the last 100 years, developments in physics have lead to a greater understanding of the actual makeup of the cosmos than ever before.
Albert Einstein, the famous German-American physicist, helped to pioneer this deeper understanding. Under the postulates of the Special Theory of Relativity, Einstein found that space and time were connected. Through this connection, variation in space must be accompanied by a variation in time. Under Newtonian physics, any object with mass has its own gravity, but space itself is “flat”. Under general relativity, any object with mass will cause curvature in space and time. This curvature is what we experience as the force of gravity. As the mass increases, so does the curvature of space and the gravitational force.
In the life cycles of stars, the more massive the star is, the more interesting its life will be. Stars that have a mass over eight times the mass of our sun put on one of the most spectacular shows the universe can put on. For stars greater than this, their end comes with a tremendous bang, in which much of the stars mass is ejected into space. This phenomena, which can be seen from distant galaxies is referred to as a supernova. The remnant for a star of such mass leads to high density neutron stars. For more massive neutron stars, the escape velocity becomes begins to approach levels nearing the speed of light. For a neutron star with a mass high enough, the escape velocity will become so great that a photon will no longer be able to escape. This stellar fragment is left with a highly dense core referred to as a singularity. As you approach the singularity, there is a point called the event horizon. This is the last chance for any particle or photon of light to turn back. Should one dare to cross into this horizon, no matter your speed, there will be no journey back.
Early on into the history of general relativity, the very concept of this “black hole” was met with skepticism. In their very nature, black holes are difficult to detect. Due to a black hole’s possession of greater than the speed of light escape velocity, light itself finds itself helplessly ensnared in the cosmic hole’s grasp. Thankfully direct detection of these phenomena is not the only way of detecting black holes in the universe. Our best hope for detection of a black hole comes from the study of the effects black holes have upon other stellar phenomena. They can even lead to other death of nearby stars, flattening the star out as it is pulled towards the more massive objects gravitational well. The result are X-rays as the doomed star is pulled into the black hole, which can be detected on Earth.
Cosmologists need not only rely of the detection of doomed stars to detect black holes. We can look for deviations of a star from a predicted orbit of its type. Another method is to observe stars that seem to periodically “disappear”. In this case, its light can be seen to periodically disappear from sight of our planet, lending evidence towards the existence of a black hole.
Black holes may only come in one shape, however, there seems to be little limit to the size. It has been postulated that at the center of our galaxy exists a super massive black hole, one which is thought to measure close to 4.5 x 106 times larger than our own star, the sun.
Penrose–Hawking singularity theorems
To form a singularity, it was postulated by Roger Penrose and Stephen Hawking potential black holes must qualify for one of these stipulations as solutions to Einstein’s field Equations:
- A situation where matter is forced to be compressed to a point (a space-like singularity)
- A situation where certain light rays comes from a region with infinite curvature.
One great explanation by Karen Masters, an astronomer at the University of Portsmouth, of the phenomena is:
“In the full and most simple General Relativistic solution for a space-time which has a Black Hole (in a vacuum), there are two singularities. One is in what we call the ‘future-light cone’ and this is the Black Hole. The other is in the ‘past-light cone’, and is called a white hole. This solution is however completely unphysical in many ways and in a real black hole (formed from the collapse of a star for example) we cannot use the vacuum solution as there is matter present, in addition to the fact that the white hole singularity disappears.”
White holes now reside in the undetectable category that black holes were resided sixty years ago. The history of white holes starts with the study of Quasars, which for many years were postulated much elusive “white holes”. However, this has proven to be an ineffective description. Quasars are themselves “powered” by gravitational forces caused by accretion disks. The ejection of electromagnetic radiation is caused by compression of the matter from the circular motion inside the black holes.
In the mathematical theory of general relativity, there is a component which has lead scientists to the possibility of a time-inverted black hole, dubbed a white hole. The idea behind a white hole is an “action-reaction” connection between black holes and their white hole counterparts. For each particle that enters a black hole past the event horizon, there is corresponding emission of a particle from the white hole. From this it is postulated that each of these particles would exist in their own universe, one particle on “each side”. It has been postulated Schwarzschild wormholes or Einstein-Rosen bridges could be theoretically formed connecting these to particles. These would allow some object, for example a photon, to try to cross in the center at which the event horizons meet. At this point, it could be possible to travel to the other corresponding hole. The concept of such a bridge was approached by John A. Wheeler and Robert W. Fuller in 1962. They found that such a path, such a wormhole would be too quickly pinched off, so much so as to not allow light from one exterior region (universe) to travel to another.
Karen Masters January 2002 http://curious.astro.cornell.edu/question.php?number=108
John Roach November 2, 2005 http://news.nationalgeographic.com/news/2005/11/1102_051102_black_hole.html
Gamma Ray Bursts by Danielle Thompson July 24, 2012Posted by missthompsondhs in Astronomy, Gamma Ray Bursts, General.
Tags: Eastern Illinois University, Gamma Ray Burst
In an extremely distance galaxy far far away, billions of light years away from Earth, something remarkable happens nearly every day. The brightest and most energetic events known to the universe perform an electromagnetic lightshow. This extravagant phenomenon releases as much energy in a few seconds as the Sun does in its entire lifetime. This amazing occurrence is thought to be connected to the explosive death of a massive star or the collision of neutron stars. These spectacular incidents, known as gamma ray bursts, that only occur on average for 20-40 seconds produce sudden intense flashes of gamma radiation that outshines everything else in the sky.
The discovery of the first gamma ray burst was a fortunate derivative of nuclear war defense using U.S. Vela satellites in the late 60’s. The US military satellites were carrying gamma ray detectors because nuclear reactions from bomb tests would give off gamma radiation. The satellites detected a flash of gamma radiation uncharacteristic of any nuclear weaponry. Surprisingly, this discovery was not of urgent concern to the US and over the next ten years with improved technology more information was collected and finally published in a scientific journal.
A later version of an Italian-Dutch satellite, BeppoSAX, launched in 1996 was equipped with not only a gamma ray but an x-ray detector allowing for the observation of the first “afterglow” of a gamma ray burst. An afterglow is caused from the burst colliding with the interstellar gases emitting longer wavelengths. Today NASA satellites are used to create the Gamma-ray Burst Coordinates Network (GCN) which coordinates space and ground-based observations to allow for better viewing of gamma ray bursts’ afterglows.
Further investigation into gamma ray bursts due to the improvements of satellites has allowed for the classification of long and short duration bursts. Long bursts have to last for more than 2 seconds and astronomers are fairly certain the cause of long duration gamma ray bursts is a rapidly rotating massive star, greater than 100 solar masses, and known as a supernova that is collapsing to form a black hole. Short duration bursts make up 30% of all bursts and are thought to be caused by neutron stars colliding. While studying long and short duration bursts, it has been discovered that no two bursts have the same light curve, this is a mystery that still plaques astronomers today.
A new possible explanation for gamma ray burst is a hypernova. Scientists refer to a hypernova as a “failed supernova”, which is still a massive star whose core has collapsed but didn’t go boom. The hypernova’s shock wave doesn’t blow off the outer layers like a supernova does. The outer layers fall into the central neutron star or black hole and produces enormous amount of heat and radiation with an outcome of higher luminosity than a supernova. A hypernova has become the favored possible explanation because gamma ray bursts are more luminous than a supernova. The actually existence of hypernovae is still a hot debate.
Some astronomers suffer from ergophobia, the fear of energy, and the fear that our galaxy the Milky Way could experience a bad day. The scenario of a gamma ray burst firing its extremely energetic radiation at planet Earth is dishearting. The intense gamma rays would be stopped by the Earth’s stratosphere but the ozone layer would be destroyed. Would the depletion of the ozone layer inevitable cause a mass extinction? Gamma ray bursts fuel the speculation that there is a conceivable end to life as we know it on Earth.
Fata Morgana and Mirages July 22, 2012Posted by pswanso233 in Astronomy, physics.
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I was scanning through the archives of the Astronomy Picture of the Day, and I saw this one which I thought looked really cool:
Interested, I looked up Fata Morgana and learned that it was a type of superior mirage. Not knowing what a superior mirage was, I had to understand what causes mirages and what the difference between an inferior and a superior mirage was.
A mirage is a real optical phenomenon, rather than a hallucination. Mirages can actually be photographed, whereas hallucinations cannot be. Mirages are caused by temperature differences in the Earth’s atmosphere. It’s here that I should probably introduce Snell’s Law and refraction, which is the bending of light through different materials. Every transparent subtance has what’s called an index of refraction, which is the ratio of the speed of light in vacuum to the speed of light in that substance. A high index of refraction indicates that light travels very slowly through the substance, whereas a low index means it doesn’t slow down much. For example, the index of refraction of water is 1.33. This means that light travels 1.33 times slower through water than it does air or vacuum. This is why a pencil looks bent if you put it in a water filled beaker while still allowing part of it to be in the air.
A high index of refraction also means light will bend more if it travels through that substance. So how exactly does this apply to mirages? Cold air is denser than warm air, so light has a harder time going through it; therefore its index of refraction is higher. If light rays from a distant source travel from cold air to hot air, they will bend away from the direction of the temperature gradient. As these light rays reach your eye, your brain traces it as though they came from a line straight ahead, similar to your eye interpreting a virtual image through a convex lens.
An inferior image is a type of mirage where an image appears to be below a real object. A common example would be a desert mirage, where the viewer thinks that there’s an oasis on the horizon. This is caused because sand tends to heat up quickly, so the air around the sand is hot and the air above it is cooler. The image you’re actually seeing is actually the sky, which is why it looks like water.
A superior image is the opposite case, where the image appears above the horizon. This is caused by what’s called a temperature inversion, where hot air exists above cold air. This tends to be more common at sea.
Anyway, as I said before, a Fata Morgana is a special case of a superior mirage. They can be seen from anywhere on Earth, but tend to be most common in Polar Regions and higher altitudes.
The special case of the superior mirage of a Fata Morgana occurs when the temperature inversion is high enough such that the light bends through it in such a way that the curvature of the light is higher than the curvature of the Earth. The viewer should be present in an atmospheric duct, which is where light rays and other electromagnetic waves bend with the curvature of the Earth. This is why these images tend to be rarer than other types of mirages.
A Fata Morgana usually looks very bizarre, and can produce stacked images on top of each other. They can also change rapidly, as if the temperature gradients change in such a way that the light no longer bends with the curvature of the Earth, they become regular superior mirages and don’t necessarily appear on the horizon anymore.
Fata Morgana is named for “The Fairy Morgana”, Morgan le Fay, who opposed King Arthur and Queen Guinevere in Arthurian legend. She was a sorceress who had affairs with some of Arthur’s knights and was also Arthur’s half-sister.
One other cool and (sort of) funny I learned is that, back in the early 1900’s, some explorers found what they called the “Crocker Land”, which was a supposedly large island that existed between Canada and Greenland. A very expensive team was sent to survey the island, but the mission cost over $100,000 (a huge sum at the time), because the island they saw was, in fact, a Fata Morgana. They were even warned by some of the natives of Greenland that it was an illusion, but they pressed on anyways and were unable to explore the Crocker Land.
There is also some interest that perhaps a Fata Morgana contributed to the sinking of the Titanic:
Gathering the Wrong Light July 21, 2012Posted by pjhsscience in Astronomy, Observatory, telescopes.
Tags: Astronomy, cosmology, Light Pollution, Observatory, science, space, stars, telescope
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Imagine for a moment, driving at night through the vast and unpopulated expanses of the western deserts of North America. Frequently, some of the most amazing photos of our night sky are taken from locations such as these and for very good reason. The only light visible is that which is being projected from the stars above. Back to yourself in the car now, you are approaching a town, a rather large town. As you get closer the lights from above start to fade as your eyes are drawn toward the glowing city. It’s not that street lamps and stoplights are more of an amazing site than our celestial blanket; it’s just that those lights are quickly becoming the only thing visible. You are experiencing the plague of metropolitan exorbitance, a form of pollution, light pollution.
Light pollution is one of the newest forms of pollution plaguing modern society. Before electric grids the night sky, even in large cities, was still an intriguing sight. As technology evolved and electricity flowed we were able to combat our limited night vision by lighting the night. As the world at night become brighter we covered the sky by uncovering what lies beneath us at night.
Lighting too has evolved throughout time. We are becoming more familiar with the glow of HID, or high intensity discharge lights, while becoming less familiar with the arrangement of the heavens. To get a view of just how encroaching light pollution can be we need only look at the animal kingdom. Lighting areas where light is not naturally present at night is having a major effect on nocturnal animals. Sea turtle hatchlings are often confused by brightly lit beaches and wander away from safe havens. Migration patterns of many species of waterfowl have been altered due to excess lighting. Feeding is a naturally performed at night for nocturnal creatures and feeding patterns have brought unwanted guests to our doorsteps due to light pollution. Lights attract bugs and bugs attract bats.
Astronomers from amateur to professional can all agree that light pollution is a great disturbance. Before even viewing a star astronomers without an enclosure cannot expect to have full dark adaption at night. The tools of astronomy are also plagued by light pollution. For instance, the Mt. Wilson Observatory just outside of Los Angeles is now operating at 11% of its original capacity due to the glowing L.A. night sky. While some stars may be visible in areas of high light pollution galaxies and nebula are greatly dimmed and very difficult to see even with advanced telescopes. New observatories are increasingly being constructed in remote areas in order combat light pollution but remote construction brings higher costs.
Limiting magnitude can be described as the faintest apparent magnitude of a celestial body capable of being detected and dependent upon equipment. Light pollution has a direct and sustained impact on the limiting magnitude in a given area. The limiting magnitude of the human eye under a completely dark sky is somewhere in the range of 7.6-8.0. At the other side of this scale, imagine yourself staring up at the night sky in a brightly lit inner-city setting. The limiting magnitude of your eye has been reduced by fifty percent to 4.0 or less. That comparison is simply applied to eyeball astronomy though, what about astronomers looking to make an observation. Under a dark sky with a 32 centimeter reflecting telescope you might just make some observations at the 18th magnitude. Again, we travel to the city where you set up your scope and find that you will only be making observations at the 13th magnitude.
For those in areas affected by light pollution there are some methods of circumventing it. Astronomers often employ narrow or high-band filters that do not allow light of certain spectral lines to pass through a telescope. The spectral lines targeted are those emitted by common vapor lamps including mercury and sodium. Though a good tool, these filters do limit the use of higher magnification.
If you wish to calculate how much light pollution will affect your astronomy work there is a simple equation to employ. The equation, I=0.01Pd-2.5 where I is the increase in sky glow, P is the population of the targeted city and d is the distance to the center of the city, works very well. This law is commonly referred to as Walker’s Law. Merle Walker proposed this relation after taking measurements of sky glow in several California cities. If you used this calculation and yielded a value of .03 that would mean that at the midway point between the horizon and zenith angle in the direction of the city the current sky would be 3% brighter than the natural background.
It is easy to see that combating light pollution would be of great benefit to society in general, the cost savings alone are staggering. Every year we waste one billion dollars lighting the night sky. Remediation of this problem is not as difficult as one might think; in fact, light pollution is the easiest of all forms of pollution to fix. Replacing old style lamps that radiate light in all directions with lamps that focus light downward is one remediation tactic. Also, we have to realize that lighting is not always necessary and we should take steps to remove lighting where it is not needed. Changing output is another effective method. Extremely bright bulbs are used in a number of lighting applications where they are not needed, limiting energy output not only reduces light pollution but also saves money.
We often light outdoor areas without a thought as to what we are losing. We may gain a little extra ease of night time navigation but we lose light at the same time. The light we lose is the light from nebula, galaxies and stars. This light has traveled a great distance, often many light years. This light has traveled those great distances through the vast reaches of outer space. This light ends its journey within our atmosphere at the hands of our lighting. Light pollution is a problem we have created but a problem that we can fix. Take a moment to look at the heavens through a dark sky and ask yourself if it is worth saving. My answer is yes.