Astronomy

Broadband spectrum of Sun

Broadband spectrum of Sun


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Broadband spectrum is one which is inclusive of all the observed wavelength ranges. In the case of the BB spectra of our Sun, there is a sharp (non-differentiable) kink in the curve in the UV-range (as shown above). What is the significance of this kink?


The point here is, that the kink you're pointing out is not belonging to the BB-spectrum of the sun. This part of the solar spectrum is a classic example for a broad class of radiation, called nonthermal radiation. The physical origin of this is in general that, every accelerated particle will radiate part of its energy away, with the experienced acceleration a, radiated power P and their relation $P sim a^2$ in a wavelength-range depending on the exact process.
The origins of those accelerations are usually thought to be strong magnetic interactions on the solar surface plasma, creating the famous sunspots and coronal loops. In those loops, electrons and protons are being shot into space, following the loop, and then return back onto the solar 'surface'. Upon return they release Bremsstrahlung, as the interactions between loop-particles and surface plasma create strong braking accelerations.

Spectrae for such processes are derived in every standard textbook about theoretical astrophysics and are given by roughly $frac{dP}{dt} sim exp(-frac{h u}{k_BT})$, which should fit the UV-part in the spectrum you gave pretty well. This now also explains the variability of this part of the solar spectrum: As the number of loops and sunspots correlates with solar activity, it is clear that the UV-bremsstrahlung-production should too.
There is however much more to this, if you are interested. Given certain violent outbreaks that happen upon release of magnetic energy, there are modulations of the emitted radio flux (also indicated in your graph) up higher-energetic regions of x-rays.


The point here is the "the solar spectrum" received from "the Sun" actually comes from different places depending on the frequency. The (stylised) smooth curve at optical and IR frequencies is pseudo-blackbody radiation from the photosphere. Pseudo-blackbody, because the radiation comes from different depths and temperatures in the photosphere, which gives rise to absorption features.

The photosphere is not hot enough to produce significant amounts of blackbody UV radiation, which accounts for the sharp "Wien tail" dying away into the UV.

The dashed lines in the UV and X-ray frequency range are emission that comes from the chromosphere and corona. i.e. They arise from a physically distinct region and thus there is no reason why they should form a continuous curve with the radiation from the photosphere.

The UV and X-ray emission is a combination of thermal radiation from hot plasma in the corona (at $sim 10^6$ K), which produces continuum bremsstrahlung and recombination lines from highly ionised metal ions like Fe X or O VI, and plasma at $10^4$-$10^5$ K in the chromosphere and transition region that is dominated by discrete recombination lines produced by ions like Mg II and C IV.

The reason that a discontinuity can persist is that the photosphere, chromosphere and corona are not radiatively coupled. i.e. The underlying photosphere is not the source of heat for the chromosphere and corona. The heating agent is the solar magnetic field.


Between the sun, harsh cleansers, pollution, and aging, our skin can become dull and wrinkled (two of our least favorite words). Thankfully, with BroadBand Light™ Therapy, you don’t have to be stuck with skin issues. Think of BBL as a multi-tasker—from age spots to sun damage—it can pretty much tackle it all.

BBL is the next generation of Intense Pulsed Light (IPL) therapy. The treatment uses short blasts of high-intensity light to produce younger-looking skin that’s firmer and more even in tone and texture. With little recovery time and no surgery, you’re going to start wondering if this anti-aging, skin rejuvenating, sun damage-reversing treatment is magic. (It’s not, it’s just science.)


Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2021 February 17
Sun Pillar with Upper Tangent Arc
Image Credit & Copyright: Mike Cohea

Explanation: This was not a typical sun pillar. Just after sunrise two weeks ago in Providence, Rhode Island, USA, a photographer, looking out his window, was suddenly awestruck. The astonishment was caused by a sun pillar that fanned out at the top. Sun pillars, singular columns of light going up from the Sun, are themselves rare to see, and are known to be caused by sunlight reflecting from wobbling, hexagon-shaped ice-disks falling through Earth's atmosphere. Separately, upper tangent arcs are known to be caused by sunlight refracting through falling hexagon-shaped ice-tubes. Finding a sun pillar connected to an upper tangent arc is extraordinary, and, initially, took some analysis to figure out what was going on. A leading theory is that this sun pillar was also created, in a complex and unusual way, by falling ice tubes. Few might believe that such a rare phenomenon was seen again if it wasn't for the quick thinking of the photographer -- and the camera on his nearby smartphone.


Broadband spectrum of Sun - Astronomy

The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared. In this review, we evaluate the current understanding of the solar photospheric composition. In particular, we present a redetermination of the abundances of nearly all available elements, using a realistic new three-dimensional (3D), time-dependent hydrodynamical model of the solar atmosphere. We have carefully considered the atomic input data and selection of spectral lines, and accounted for departures from local thermodynamic equilibrium (LTE) whenever possible. The end result is a comprehensive and homogeneous compilation of the solar elemental abundances. Particularly noteworthy findings are significantly lower abundances of C, N, O, and Ne compared to the widely used values of a decade ago. The new solar chemical composition is supported by a high degree of internal consistency between available abundance indicators, and by agreement with values obtained in the Solar Neighborhood and from the most pristine meteorites. There is, however, a stark conflict with standard models of the solar interior according to helioseismology, a discrepancy that has yet to find a satisfactory resolution.


Reflection

Saturn: View of Saturn and it's rings from Cassini, taken just after Saturn equinox on August 12, 2009. The Sun is just above the plane of the rings illuminating portions of the planet, rings, and a few of its moons.
Credit: NASA/JPL/Space Science Institute

While stars are the main long-lasting sources of visible light in space, the light that they emit can sometimes reflect off other objects. The most noticeable example is the Moon, which reflects the light from the Sun. The colors and spectra of such objects are the same as those of the primary source of light, for instance the Moon has a color similar to that of the Sun and the same spectrum. The Moon does not generate its own light, and the amount of the surface we see depends on the angle from which we are observing it. When the Moon is between the Earth and the Sun, we cannot see the Moon at all.

The light from other planets in the solar system is also reflected light from the Sun. All planets reflect the light from their star, which is the only way that we can see them with our eyes. However, most planets are so far away that the light they reflect is overwhelmed by the direct light shining from their star. Maybe one day an astronomer will be able to figure out another way to see these planets using visible light.

There is a class of nebulae in the galaxy that only reflects light, and these are naturally named reflection nebulae. In these cases light is reflected off small dust particles like small mirrors, changing its direction and allowing us to see the clouds containing the dust. As with the case of the planets and their host star, the reflected light appears to be much fainter than the light from the original source.

Barnard's Merope Nebula: Known as Barnard's Merope Nebula because it was first identified by E. E. Barnard in 1891 and is near the bright star Merope in the Pleiades nebulosity. It was later cataloged as IC 349.
Credit: Image courtesy Johannes Schedler / panther-observatory

Merope Spectrum: The top spectrum is of the star Merope, one of the Seven Sisters in the constellation known as the Pleiades. The bottom spectrum is of the light reflected off of dust grains behind the nebula, back to Earth. Only a tiny portion of the nebula from the accompanying image was used to take this image. The spectra are identical. This type of nebula is called a reflection nebula. The nebula is much fainter (by a factor of 1 million per square arcsec of sky) than the star, so that even with an exposure of 18,000 seconds, the signal is much weaker than that of the star, the exposure for which, with the same instrument, is only a few seconds. The relatively weak signal accounts for the fluctuations (noise) in the nebular spectrum. The spectra were recorded using a high resolution spectrograph fed by a 36-inch telescope (the Kitt Peak National Observatory Coulde Feed). For more information about this spectrum, see Barentine, John C. and Esquerdo, Gilbert A. 1999, ApJ, 117, 1402.
Credit: Spectrum courtesy J. Barentine and G. Esquedero / American Astronomical Society


Features

Water resistant: Don&rsquot assume your broad-spectrum sunscreen will protect you when you&rsquore swimming or sweating. Although sunscreens are no longer designated &ldquowaterproof&rdquo, only those designated &ldquowater resistant&rdquo will maintain effectiveness while you swim or sweat (for up to 40 minutes). Those designated &ldquovery water resistant&rdquo will work for up to 80 minutes.

Reef safe: When you swim in the ocean, a fair amount of sunscreen ends up in the water. Environmentally friendly sunscreens don&rsquot have chemicals (like oxybenzone or octinoxate) that have been proven to damage reefs. Some places with coral reefs, like Hawaii, have banned the sale of sunscreens containing these ingredients.

Spray: A great feature for people with limited mobility or who are traveling solo to the beach or pool is spray sunscreen to hit those hard-to-reach places. Parents often prefer sprays because they&rsquore easier to apply to children. Be sure to apply an even coat, and avoid inhaling the product.

Lightweight: If you have oily skin, you may want to avoid moisturizing or creamy sunscreens. Many broad-spectrum sunscreens offer non-greasy formulas that absorb easily into your skin, often leaving a matte or dry-touch finish. Select ones that are non-comedogenic if you have acne-prone skin, as these won&rsquot clog your pores.

Sensitive skin: If you have sensitive skin, select a product that&rsquos labeled hypoallergenic and fragrance free. You may also benefit from a product free from parabens and other chemical agents.

Face: There are also broad-spectrum sunscreens formulated specifically for the more delicate face area. These tend to be oil-free and pricier, but are good for sensitive skin as body sunscreens may cause irritation on the face.


Plasma density profile evaluation in broadband reflectometry using a neural network

F.D. Nunes , . M.E. Manso , in Fusion Technology 1996 , 1997

Broadband reflectometry is a diagnostic suited to measure plasma density profiles in present and forthcoming fusion devices like ITER. A major issue is the possibility of using profile measurements from reflectometry at the plasma boundary as a reference for the magnetic diagnostics in long pulse discharges. This requires fast algorithms to process data on-line. Here we present an approach to profile evaluation, based on a neural network, that has great potentialities to meet the speed and accuracy requirements for the position control reflectometer on ITER. The proposed network is a two-layer perceptron which is trained with a set of expected density profiles. We adopted a Fourier series to represent the profile, thus the network output is a set of Fourier coefficients and the entire profile can be conveniently reconstructed with a small number of parameters. Since the Abel inversion integral is not used the algorithm is very fast. In addition, simulations show that the proposed solution is robust to input noise.


Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2017 September 7
The Flash Spectrum of the Sun
Image Credit & Copyright: Yujing Qin (University of Arizona)

Explanation: In clear Madras, Oregon skies, this colorful eclipse composite captured the elusive chromospheric or flash spectrum of the Sun. Only three exposures, made on August 21 with telephoto lens and diffraction grating, are aligned in the frame. Directly imaged at the far left, the Sun's diamond ring-like appearance at the beginning and end of totality brackets a silhouette of the lunar disk at maximum eclipse. Spread by the diffraction grating into the spectrum of colors toward the right, the Sun's photospheric spectrum traces the two continuous streaks. They correspond to the diamond ring glimpses of the Sun's normally overwhelming disk. But individual eclipse images also appear at each wavelength of light emitted by atoms along the thin, fleeting arcs of the solar chromosphere. The brightest images, or strongest chromospheric emission, are due to Hydrogen atoms. Red hydrogen alpha emission is at the far right with blue and purple hydrogen series emission to the left. In between, the brightest yellow emission is caused by atoms of Helium, an element only first discovered in the flash spectrum of the Sun.


Broadband spectrum of Sun - Astronomy

If you didn't get the joke, you probably didn't understand the science behind it. If this is the case, it's a chance for you to learn a little astronomy.

Read Jupiter Scientific's report on the coronavirus:
Find out one possibly major error in the US governement's fight to stop its spread.
Discover an important method to help project yourself.


Astronomy Joke 1:
Q: What is Preparation A?
A: It is the name of an over-the-counter product used to relieve the pain and suffering of asteroids.
See explanation


Astronomy Joke 2:
When Mr. Leno of the Tonight Show went J-walking and asked pedestrians some science questions, he discovered some amazing new facts about the universe:

Jay Leno: "Why does dew appear on plants in the morning when the Sun comes up?" A waitress: "Is it because the Sun makes them perspire?"

Jay Leno: "Why does the Moon orbit the Earth?" An auto mechanic: "To get to the other side?"

Jay Leno: What are magnets?" A taxi driver: "Are they the things crawling over a week-old dead cat?"

Jay Leno: Which is more useful, the Sun or the Moon?" A thirteen-year old: [Pause] "I think it's the Moon because the moon shines at night when you want the light, whereas the Sun shines during the day when you don't need it."
See explanation


Check out Jupiter Scientific's Virtual Astronomer Pages with the Most Spectacular Internet Images of
Messier Objects
The Solar System
The Milky Way and the Universe
Miscellaneous Objects
Best Astronomical Images on the Web
(At these webpages, click on the various links to see the images.)


Astronomy Joke 3:
It is reported that Copernicus' parents said the following to him at the age of twelve: "Copernicus, young man, when are you going to come to terms with the fact that the world does not revolve around you."
See explanation


Astronomy Joke 4:
The Official Unabashed Scientific Dictionary defines black holes as what you get in black socks.
See explanation


Astronomy Joke 5:
"Whatever the missing mass of the universe is, I hope it's not in cockroaches." – a New York City tenant.
See explanation


Astronomy Joke 6: A limerick about Edmund Halley

From the public, his discovery brought cheers.
From his wife, it drew nothing but torrents of tears.
"For you see," said Ms. Halley,
"He used to come daily
Now he comes once every 70 years!"
See explanation


Astronomy Joke 7:
An English major at a university was taking an astronomy course to satisfy the science requirement. During the last lecture of the semester, the professor spoke about some of the more exotic objects in the universe including black holes. Despite his teacher's enthusiasm, the student showed no interest, as was the case for all his astronomy classes during the semester. When the bell rang, the student turned to his friend and said, "The prof says that black holes are interesting, but I think they suck."
See explanation

DANGER. BLACK HOLE LOCATED TO THE RIGHT. DON'T CLICK THERE:


Astronomy Joke 8:
An astronomy major had a part time job working in the university's off-campus housing office. One day, a fellow student, upon entering the office in thought about the morning lecture, asked, "What is an astronomical unit?" To which the astronomy major replied, "One helluva big apartment."
See explanation


Are you interested in learning more about cosmologoy and astronomy?
Read a review about an astronomy book,
Or visit Jupiter Scientific's Reports and News in Astronomy,
Or read some chapters from the Bible According to Einstein.


Astronomy Joke 10:
Q: Before docking with the International Space Station, what must the pilot of a space module first do?
A: Put money in a parking meteor.
See explanation


Astronomy Joke 11:
Q: If you ask a Russian cosmonaut when is his favorite moment to snack, how does he answer?
A: "Launch time."
See explanation


Astronomy Joke 12:
Star light, star bright,
First star I see tonight.
I wish I may, I wish I might,
Oh f****, it's just a satellite.
See explanation


Astronomy Joke 13:
Famous Astronomer Quote: I was up all night wondering where the Sun had gone . then it dawned on me.


Astronomy Joke 14:
Sherlock Holmes and Doctor Watson were sleeping out in the wild. At 2:00 am in the morning, Holmes woke up Watson and he asked, "Watson, look up and pray tell me what you presume."
Watson replied, "I see a vast Universe, full of stars and wonder. There is Venus over there. And the Moon is half lit. I know that lurking at the center of our galaxy is a black hole, and that gamma ray bursts occasionally blast at us, that there are billions and billions of planets out there, some of which must harbor life. We are not alone."
Watson would have continued but Holmes abruptly cut him off, "No, Watson, you idiot! Somebody stole our tent!"
See explanation


Astronomy Joke 15:
When the astronomy department found out their famous professor was not going to get the Nobel prize this year, they decided to hold a party for him anyway and give him a constellation prize instead.
See explanation


Astronomy Joke 16:
Well known are the words of Neil Armstrong when he first walked on the moon: "One small step for man, one giant leap for mankind." However, few people know of NASA's coverup of a very embarressing event took place an hour later. We, at Jupiter Scientific, have recently obtained a transcript of the conversation that transpired:
Niel Armstrong: "Oh sh***, Mission Control, I just stepped on Buzz Aldrin's toe. What should I do? Over."
Mission Control: "What do you think? Apollogize."
See explanation


This jokes on this page were compiled by the staff of Jupiter Scientific, an organization devoted to the promotion of science through books, the internet and other means of communication.

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Gamma-Rays

The term gamma ray is used to denote electromagnetic radiation from the nucleus as a part of a radioactive process. The energy of nuclear radiation is extremely high because such radiation is born in the intense conflict between the nuclear strong force and the electromagnetic force, the two strongest basic forces. The gamma ray photon may in fact be identical to an x-ray, since both are electromagnetic rays the terms x-ray and gamma rays are statements about origin rather than implying different kinds of radiation.

In interactions with matter, gamma rays are ionizing radiation and produce physiological effects which are not observed with any exposure of non-ionizing radiation, such as the risk of mutations or cancer in tissue.


Watch the video: What is Kirchoffs Law? Blackbody and Cavity Radiation! (December 2022).