NASA Scientists Observe the Sun in Different Wavelengths

This collage of solar images from NASA's Solar Dynamics Observatory (SDO) shows how observations of the sun in different wavelengths helps highlight different aspects of the sun's surface and atmosphere. 

The collage also includes images from other SDO instruments that display magnetic and Doppler information. 

Credit: NASA/SDO/Goddard Space Flight Center.

Taking a photo of the sun with a standard camera will provide a familiar image: a yellowish, featureless disk, perhaps coloured a bit more red when near the horizon since the light must travel through more of Earth's atmosphere and consequently loses blue wavelengths before getting to the camera's lens.

The sun, in fact, emits light in all coluors, but since yellow is the brightest wavelength from the sun, that is the colour we see with our naked eye -- which the camera represents, since one should never look directly at the sun. When all the visible colours are summed together, scientists call this "white light."

Specialist instruments, either in ground-based or space-based telescopes, however, can observe light far beyond the ranges visible to the naked eye.

Different wavelengths convey information about different components of the sun's surface and atmosphere, so scientists use them to paint a full picture of our constantly changing and varying star.

Yellow light of 5800 Angstroms, for example, generally emanates from material of about 10,000 degrees F (5700 degrees C), which represents the surface of the sun.

Extreme ultraviolet light of 94 Angstroms, on the other hand, comes from atoms that are about 11 million degrees F (6,300,000 degrees C) and is a good wavelength for looking at solar flares, which can reach such high temperatures.

By examining pictures of the sun in a variety of wavelengths - as is done through such telescopes as NASA's Solar Dynamics Observatory (SDO), NASA's Solar Terrestrial Relations Observatory (STEREO) and the ESA/NASA Solar and Heliospheric Observatory (SOHO) - scientists can track how particles and heat move through the sun's atmosphere.

We see the visible spectrum of light simply because the sun is made up of a hot gas - heat produces light just as it does in an incandescent light bulb but, when it comes to the shorter wavelengths, the sun sends out extreme ultraviolet light and x-rays because it is filled with many kinds of atoms, each of which give off light of a certain wavelength when they reach a certain temperature.

Not only does the sun contain many different atoms - helium, hydrogen, iron, for example -- but also different kinds of each atom with different electrical charges, known as ions.

Each ion can emit light at specific wavelengths when it reaches a particular temperature. Scientists have catalogued which atoms produce which wavelengths since the early 1900s, and the associations are well documented in lists that can take up hundreds of pages.

Solar telescopes make use of this wavelength information in two ways. For one, certain instruments, known as spectrometers, observe many wavelengths of light simultaneously and can measure how much of each wavelength of light is present.

This helps create a composite understanding of what temperature ranges are exhibited in the material around the sun. Spectrographs don't look like a typical picture, but instead are graphs that categorise the amount of each kind of light.

Massive Solar Flare: HD Still

NASA image captured March 6, 2012

View a video of this event here

The sun erupted with one of the largest solar flares of this solar cycle on March 6, 2012 at 7PM ET.

This flare was categorized as an X5.4, making it the second largest flare, after an X6.9 on August 9, 2011, since the sun’s activity segued into a period of relatively low activity called solar minimum in early 2007.

The current increase in the number of X-class flares is part of the sun’s normal 11-year solar cycle, during which activity on the sun ramps up to solar maximum, which is expected to peak in late 2013.

About an hour later, at 8:14 PM ET, March 6, the same region let loose an X1.3 class flare. An X1 is 5 times smaller than an X5 flare.

These X-class flares erupted from an active region named AR 1429 that rotated into view on March 2.

Prior to this, the region had already produced numerous M-class and one X-class flare. The region continues to rotate across the front of the sun, so the March 6 flare was more Earthward facing than the previous ones.

It triggered a temporary radio blackout on the sunlit side of Earth that interfered with radio navigation and short wave radio.



In association with these flares, the sun also expelled two significant coronal mass ejections (CMEs), which are travelling faster than 600 miles a second and may arrive at Earth in the next few days.

In the meantime, the CME associated with the X-class flare from March 4 has dumped solar particles and magnetic fields into Earth’s atmosphere and distorted Earth's magnetic fields, causing a moderate geomagnetic storm, rated a G2 on a scale from G1 to G5.

Such storms happen when the magnetic fields around Earth rapidly change strength and shape.

A moderate storm usually causes aurora and may interfere with high frequency radio transmission near the poles.

This storm is already dwindling, but the Earth may experience another enhancement if the most recent CMEs are directed toward and impact Earth.

In addition, last night’s flares have sent solar particles into Earth’s atmosphere, producing a moderate solar energetic particle event, also called a solar radiation storm.

These particles have been detected by NASA’s SOHO and STEREO spacecraft, and NOAA’s GOES spacecraft.

At the time of writing, this storm is rated an S3 on a scale that goes up to S5. Such storms can interfere with high frequency radio communication.

Besides the August 2011 X-class flare, the last time the sun sent out flares of this magnitude was in 2006. There was an X6.5 on December 6, 2006 and an X9.0 on December 5, 2006.

Like the most recent events, those two flares erupted from the same region on the sun, which is a common occurrence.

Credit: NASA/SOHO

Nasa SOHO Spacecraft: Nearing optimum position

An artist's impression of STEREO spacecraft surrounding the Sun.

NASA's twin STEREO probes moved into position on opposite sides of the sun, and they are now beaming back uninterrupted images of the entire star - front and back.

"For the first time ever, we can watch solar activity in its full three-dimensional glory," says Angelos Vourlidas, a member of the STEREO science team at the Naval Research Lab in Washington, DC.

Four years after launch NASA's two STEREO spacecraft are now 180 degrees apart and able to image the entire Sun.
Picture: NASA

NASA STEREO, SOHO Spacecraft Catch Comet Diving Into Sun

Solar physicists at the University of California, Berkeley, have tracked a comet through the low solar atmosphere, deeper into the sun than ever before, before it presumably evaporated in the 100,000-degree heat.

Using instruments aboard NASA's twin STEREO spacecraft, four post-doctoral fellows at UC Berkeley's Space Sciences Laboratory were able to track the comet as it approached the sun and estimate an approximate time and place of impact.

STEREO (Solar TErrestrial RElations Observatory), launched in 2006, consists of identical spacecraft orbiting the sun, one ahead of Earth and one behind Earth, providing a stereo view of the sun.

The researchers then looked at data from the ground-based Mauna Loa Solar Observatory in Hawaii, and found images in the predicted spot of what appears to be a comet approaching the edge of the sun from behind the solar disk.

"We believe this is the first time a comet has been tracked in 3-D space this low down in the solar corona," said Claire Raftery, a post-doctoral fellow newly arrived at UC Berkeley from Dublin's Trinity College.

The team will present its data and images during a 5:30-6:30 p.m. poster session on Monday, May 24, at the Miami, Fla., meeting of the American Astronomical Society.

Sungrazing comets, composed of dust, rock and ice, are seldom tracked close to the sun because their brightness is overwhelmed by the solar disk. This comet apparently survived the heat of the corona and disappeared in the chromosphere, evaporating in the 100,000-degree (Kelvin) heat.

Raftery and her colleagues, Juan Carlos Martinez-Oliveros, Samuel Krucker and Pascal Saint-Hilaire, concluded that the comet was probably one of the Kreutz family of comets, a swarm of Trojan or Greek comets ejected from their orbit in 2004 by Jupiter, and that it made its first and only loop around the sun. The swarm probably resulted from the disintegration of a larger comet.