ballpoint pen drawing
The Sun oscillates and vibrates at many frequencies, like an ocean surface or …like a bell. Certain frequencies are amplified by constructive interference(wave propagation) and the turbulence “rings” the sun like a bell. Unfortunately, sound does not carry through the vacuum between the Sun and the earth, so we have to “listen" to the oscillations by looking at the motions of material on the surface of the Sun. With the right instruments, scientists can "hear" this ringing or pulsations from the Sun. To do this, they use an instrument called a Michelson Doppler Imager (MDI), mounted on the SOHO spacecraft and the Helioseismic and Magnetic Imager (HMI), one of the three instruments that make up the Solar Dynamics Observatory (SDO).
Although direct study of its interior is impossible —mostly because the Sun is nearly opaque to electromagnetic energy, insights into the conditions within the Sun may be gained by observing oscillating waves, rhythmic inward and outward motions of its visible surface. These oscillations on the surface are due to sound waves generated and trapped inside the sun. Sound waves are produced by pressure fluctuations in the turbulent convective motions of the sun’s interior. These trapped sound waves set the sun vibrating in millions of different patterns or modes. Using this acoustic energy, we can “see into the Sun”, just as geologists use seismic waves to study the structure of the Earth, the discipline of helioseismology makes use of acoustic pressure waves (infrasound) traversing the Sun’s interior. These oscillations are seen as volumes of gas called granules near the Sun’s surface that rise and fall with a particular frequency. It is like seeing the rolling motions of convection cells on the surface of boiling water. This happens very close to the surface where the flow of energy that started in the nuclear reactions in the core reaches the surface and suddenly escapes. The sound from the convection is then trapped and filtered inside the sun to produce the solar music.
Helioseismologists can use the properties of these waves to determine the temperature, density, composition, and motion of the interior of the sun. The spectral lines emitted from gas moving upwards will be slightly Doppler-shifted to the blue; spectral lines from gas moving downwards will be slightly Doppler-shifted to the red. In this way the rolling motions of convection near the Sun’s surface can be mapped out. There are three types of oscillations. Pressure modes (p-modes) are sound waves trapped in the temperature gradient (like an echo bouncing around inside a cavern). Fundamental modes (f-modes) or surface gravity waves are caused by gravitational interactions with the sun’s surface and resemble ocean waves. Gravity modes (g-modes) are not completely understood, but they are believed to be the result of buoyancy effects. All the known pressure and fundamental modes (some 10 million) have oscillation periods of less than 18 minutes, and most are around 5 minutes. The gravity modes are not known conclusively to exist, but they are predicted to have periods of 40 minutes or longer (160-min).
In The Imitation Game, Benedict Cumberbatch plays Alan Turing, the genius British mathematician, logician, cryptologist and computer scientist who led the charge to crack the German Enigma Code that helped the Allies win WWII. Turing went on to assist with the development of computers at the University of Manchester after the war, but was prosecuted by the UK government in 1952 for homosexual acts which the country deemed illegal.
Release date: November 21, 2014 (official trailer)
On land, sunlight illuminates a world that’s bright and bursting with color. But in the ocean, light and color diminish as the water gets deeper. Take a look at what happens to light as it moves through the water, and how marine organisms have adapted.
Learn more in our traveling exhibition, Creatures of Light.
The International Space Station as seen from Space Shuttle Atlantis [3032x2004]
Last week the Solar Dynamics Observatory (SDO) caught a glimpse of the Moon transiting the sun. Here is that sequence in a variety of wavelengths.
Rising from a sea of dust and gas, the legendary Horsehead Nebula emerges. This amazing NASA’s Hubble Space Telescope close-up reveals the cloud’s intricate structure. Also known as Barnard 33, the Horsehead is a cold, dark cloud of gas and dust, silhouetted against the bright nebula, IC 434. The bright area at the top left edge is a young star still embedded in its nursery of gas and dust. The top of the nebula also is being sculpted by radiation from a massive star located out of view.
Image Credit: NASA, NOAO, ESA and The Hubble Heritage Team (STScI/AURA)
Smith Chart visual representation of interaction between resistive and reactive components.
I’m still very much in the diatom game. This is Gyrosigma attenuatum.
Star Formation Triggers
This composite image, combining data from NASA’s Chandra X-ray Observatory and Spitzer Space Telescope shows the star-forming cloud Cepheus B, located in our Milky Way galaxy about 2,400 light years from Earth. A molecular cloud is a region containing cool interstellar gas and dust left over from the formation of the galaxy and mostly contains molecular hydrogen. The Spitzer data, in red, green and blue shows the molecular cloud (in the bottom part of the image) plus young stars in and around Cepheus B, and the Chandra data in violet shows the young stars in the field.
The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission. The Spitzer data showed whether the young stars have a so-called “protoplanetary” disk around them. Such disks only exist in very young systems where planets are still forming, so their presence is an indication of the age of a star system.
These data provide an excellent opportunity to test a model for how stars form. The new study suggests that star formation in Cepheus B is mainly triggered by radiation from one bright, massive star (HD 217086) outside the molecular cloud. According to the particular model of triggered star formation that was tested — called the radiation- driven implosion model — radiation from this massive star drives a compression wave into the cloud triggering star formation in the interior, while evaporating the cloud’s outer layers.
Different types of triggered star formation have been observed in other environments. For example, the formation of our solar system was thought to have been triggered by a supernova explosion. In the star-forming region W5, a “collect-and-collapse” mechanism is thought to apply, where shock fronts generated by massive stars sweep up material as they progress outwards. Eventually the accumulated gas becomes dense enough to collapse and form hundreds of stars. The radiation-driven implosion model mechanism is also thought to be responsible for the formation of dozens of stars in W5. The main cause of star formation that does not involve triggering is where a cloud of gas cools, gravity gets the upper hand, and the cloud falls in on itself.
Image Credit: NASA/CXC/JPL-CALTECH/PSU/CFA