The Solar Corona

This is information for the text The Solar Corona by Leon Golub and Jay M. Pasachoff

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Cambridge University Press
ISBN 0 521 48082 5 hardback
ISBN 0 521 48535 5 paperback

Table of contents:
1. Introduction
2. Brief history of coronal studies
3. The coronal spectrum
4. The solar cycle
5. Ground-based observations
6. Observations from space: I. The first 30 years
7. Activity of the inner corona
8. Observations from space: II. Recent missions
9. Solar flares & the corona
10. Solar-terrestrial physics

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See also the errata page for this book:

A variety of solar information, including updates on sunspots and daily images through various filters, is available through the homepage for Pasachoff's Astronomy: From the Earth to the Universe.


Engineers Successfully Regain Control of SOHO Spacecraft

Spacecraft controllers successfully regained control of the Solar and Heliospheric Observatory (SOHO) spacecraft yesterday after sending a series of commands directing the spacecraft to fire thrusters and turn its face and solar power panels fully towards the Sun.

The SOHO flight operations team reported success in the maneuver, which is called attitude recovery, at 2:29 p.m. EDT Wednesday, the first time the joint European Space Agency (ESA) and NASA spacecraft has been controlled from the ground since SOHO spun out of control and communication was lost on June 24.

"It's a big step forward in our recovery plan for SOHO," says Dr. John Credland, ESA's head of scientific projects. "We were never quite sure that we would manage to make the spacecraft point back towards the Sun, which is essential for its proper operation. I congratulate our joint ESA-NASA team, helped by our industrial contractors, who have accomplished it."

"This is the best news we've had from SOHO in a long time," said Dr. George Withbroe, Director of the Sun-Earth Connection science theme at NASA Headquarters, Washington, DC. "Despite the gloomy early days after the loss, we always stayed hopeful that the resourceful people on the team could save the day. We're not there yet -- we still have to see if the scientific instruments survived. But this gives us reason to hope."

"Now we start a comprehensive check of all the spacecraft's systems and scientific instruments," said Dr. Bernhard Fleck, ESA's project scientist for SOHO. "We shall take our time and go step by step, in consultation with the 12 scientific teams in Europe and the United States, who provided the instruments. In some cases the instruments have been through an ordeal of heat or cold, with temperatures approaching plus or minus 100 degrees Celsius (212 degrees Fahrenheit). But I'm cautiously optimistic that SOHO can win back much of its scientific capacity for observing the Sun."

SOHO operates at a special vantage point 1.5 million kilometers (about one million miles) out in space, on the sunward side of the Earth. The spacecraft was built in Europe and it carries both American and European instruments, with international science teams. NASA launched SOHO and has responsibility for operations at NASA's Goddard Space Flight Center, Greenbelt, MD.

After its launch on Dec. 2, 1995, SOHO revolutionized solar science by its special ability to observe simultaneously the interior and atmosphere of the Sun, and particles in the solar wind and the heliosphere. Apart from amazing discoveries about flows of gas inside the Sun, giant "tornadoes" of hot, electrically charged gas, and clashing magnetic field-lines, SOHO also proved its worth as the chief watchdog for the Sun, giving early warning of eruptions that could affect the Earth.

In April 1998, SOHO's scientists celebrated two years of successful operations and the decision of ESA and NASA to extend the mission to 2003. The extension would enable SOHO to observe intense solar activity, expected when the count of sunspots rises to a maximum around the year 2000. It would remain the flagship of a multinational fleet of solar spacecraft, including the ESA/NASA Ulysses and Cluster II missions.


The dormant Solar and Heliospheric Observatory (SOHO) spacecraft has sent temperature and electrical data to ground controllers, information which could help in the satellite's recovery. The SOHO Recovery Team is working to recharge the spacecraft's batteries, which in turn will allow the team to assess the spacecraft's overall health and condition of the scientific instruments.

The SOHO data was received Aug. 8, six days after the spacecraft's first signal since the end of June, at NASA's Goddard Space Flight Center, Greenbelt, MD.

"This is the best news I've heard since we lost contact with SOHO," said Roger Bonnet, Director of Science for the European Space Agency (ESA), NASA's partner in the mission. "I never gave up hope of some recovery of this fantastic mission. We should just hope that the damage sustained by SOHO's enforced period of deep freeze does not affect the scientific payload too much."

Following analysis of the expected onboard conditions by engineers from ESA and Matra Marconi Space, the spacecraft's builders, commands were sent through the NASA Deep Space Network station at Goldstone, CA. These sequences were designed to divert the available solar array power into a partial charging of one of the onboard batteries.

After 10 hours of charging, the telemetry was commanded on and seven full sets of data about the onboard status were received, including information on temperatures and voltages for payload instruments. After one minute, ground controllers switched off the telemetry to preserve onboard resources.

Because of the spacecraft's orientation, some temperatures are colder than normal, and some are hotter than normal, as expected. The instruments' condition will not be known with certainty until attempts are made to activate them at the end of the recovery sequence. The hydrazine fuel is likely to be partially frozen.

Data on voltages and currents in individual units indicated one of the two batteries on board the spacecraft is almost fully charged. Attempts to recharge the second battery are underway.

With the battery-charging technique proven successful, the team has requested a full 24-hour coverage of SOHO to attempt a more complete charging. The Deep Space Network has accepted this request on an emergency basis and will give it priority over other scheduled network activities.

"I am truly satisfied with the information the data we acquired gives us," said ESA's Francis Vanderbussche, who is in charge of the SOHO Recovery Team at Goddard. "Conditions onboard are as good as we expected them to be."

The team is working on the next series of procedures, which will try to thaw the onboard hydrazine fuel, currently at zero degrees Celsius. Thawing the fuel will allow controllers to re-establish control of the spacecraft. The thawing will be attempted later this week after both batteries are fully charged.

The delicate recovery activities are being directed by the ESA SOHO project team from the NASA Operation Center at Goddard.

SOHO completed its nominal two year mission in April 1998. The spacecraft has already achieved spectacular results concerning the dynamics of the solar interior and has given a comprehensive view of the solar corona. Its mission had recently been extended to 2003 to cover the upcoming period of maximum solar activity expected to peak in 2001.

More information on SOHO, including mission status reports, is available on the Internet at the new ESA science website at: or at:

SOHO dies

The Solar and Heliospheric Observatory (SOHO) lost contact with Earth when undergoing a maneuver on June 24. Efforts are continuing to establish contact with the spacecraft, but hopes are diminishing that it will be recovered. There is still some hope that the problem comes from the solar panels being oriented away from the sun as the spacecraft spins, and that in some weeks they will be better oriented and that the spacecraft can be saved. Bulletins appear on the SOHO site. The spacecraft was launched on December 2, 1995, and has very successfully completed its primary two-year mission, but it has certainly been hoped that it would continue sending its high-quality data back to Earth through the solar maximum of 2000.

H.Mucke and J. Meeus: Canon of Solar Eclipses, -2003 to +2526

The 1992 printing is available from:

The price, including a diskette with a program to calculate local circumstances as well as mailing by registered surface book post, is ATS 1085.-; for air mail delivery, ATS 190.- should be added. Please send a check in ATS, payable to Astronomisches Bureau, Hasenwartgasse 32, A-1238 Vienna, Austria.

Partial, Annular, and Total Solar Eclipses in 1999 and 2000

16 February 1999. An annular eclipse with annularity visible in a path across Australia from west to northeast, extending from north of Perth to near Cairns. A partial eclipse will be visible in the south Atlantic Ocean, southern Africa and Madagascar except its northern tip, Indonesia except for northwestern Sumatra, the extreme southern Malaysian peninsula including Singapore, the southern Philippines, Papua New Guinea, Australia, the southern island of New Zealand, and most of Antarctica. The magnitude will be 99.3%, with a maximum duration of 40 seconds.

11 August 1999. A total eclipse with totality beginning in the Atlantic off the northeast American coast, reaching Europe at Land's End in Britain, and extending through parts of France, Belgium, Luxembourg, Germany, Austria, Hungary, Serbia, Romania, Bulgaria, Turkey, Iraq, Iran, Pakistan, and India. The magnitude of totality is 103%, and the maximum eclipse will occur over Romania and last 2 minutes 23 seconds. The path is especially narrow, never exceeding 113 km. The partial eclipse will be visible from northeastern US and Canada at sunrise, Greenland, all of Europe, most of Asia except the extreme east, and with the eastern limit extending southward through Bangaladesh and east of Calcutta in India. The northern half of Africa will also see a partial eclipse.


There will be no total or annular solar eclipses in the year 2000.

5 February 2000. The partial solar eclipse, with a magnitude of 59%, will be visible only from Antarctica.

1 July 2000. The partial eclipse will be visible mainly from the extreme southern Pacific Ocean, not quite extending down to Antarctica. The magnitude will be 48%. The only land from which the partial eclipse will be visible is the southern halves of Chile and Argentina.

31 July 2000. The partial eclipse will be visible from the northern part of Greenland, the northwest of the continental United States (from a line extending through the western parts of the Dakotas through Colorado, northwest Utah, mid-Nevada, and mid-California), western Canada, Alaska, northern Russia, and northern Scandinavia. The magnitude will be 60%.

25 December 2000. The partial eclipse will be visible through all of North America except Alaska, Central America as far south as Nicaragua, and the extreme northern tip of Columbia and Venezuela, including Aruba and many other Caribbean islands extending southeast from the U.S. to the Leeward Islands. It will extend as far east as the Azores. The magnitude will be 72%.

Web sites:
International Astronomical Union Working Group on Eclipses:

Fred Espenak, Fifty Year Canon of Solar Eclipses: 1986-2035, NASA Reference Publication 1178 Revised, July 1987.

Leon Golub and Jay M. Pasachoff, The Solar Corona, Cambridge University Press, 1998.

Jay M. Pasachoff, Astronomy: From the Earth to the Universe, 5th ed., Saunders College Publishing, 1998.

                                Provided by Jay M. Pasachoff
                                Williams College, Williamstown, MA
                                        01267, USA
                                Chair, Working Group on Eclipses of
                                the International Astronomical Union

TRACE Satellite Is Working Well

The Transition Region and Coronal Explorer spacecraft was successfully launched on April 1st to make high-resolution observations of these regions of the outer solar atmosphere and is working well. TRACE Web sites are at Lockheed and at the Smithsonian Observatory.

Reports on the 1998 Total Solar Eclipse

Espenak homepage with reports on 1998 eclipse

Southwest Research Institute 1998 eclipse homepage

High Altitude Observatory 1998 eclipse homepage

1998 Solar Eclipse Displayed with RedShift 2 Software


SOHO February 26 1998 Eclipse Observations

A SOHO eclipse page has been set up to summarize pertinent information, the requests to the SOHO community for joint observations, and the SOHO observing plans.

Eclipse, Satellite Solar Slides

Eight radial-filter eclipse images from the National Center for Atmospheric Research and a variety of coronal images from the Solar Maximum Mission are viewable on the Web and can be ordered as slides.

X-Ray Images from TRACE

Leon Golub and colleagues have put up the first two TRACE XUV images:

Note that these were taken during a large proton storm, and the image stabilization system has not yet been turned on.

Eclipses Imaged from Space

The views from the GOES satellite in orbit around the Earth showing the progress of the 26 February 1998 and 11 July 1991 eclipses across the face of the Earth are available at


The first images from NASA's Transition Region and Coronal Explorer (TRACE) spacecraft reveal activity in the solar atmosphere in stunning detail and include the first detailed observations of a magnetic energy release, called a magnetic reconnection.

The magnetic reconnection was observed on May 8, 1998, in a region of the solar atmosphere where two sets of perpendicular magnetic loops expanded into each other. Magnetic reconnection occurs when magnetic fields "snap" to a new, lower energy configuration, much like when a twisted rubber band unwinds or breaks. A magnetic reconnection can release vast amounts of energy and is responsible for explosive events on the Sun, such as flares, that can cause communication and power system disruptions on Earth.

High resolution movies of a relatively small but clear magnetic reconnection event and other spectacular solar activity observed by TRACE were presented today during the spring meeting of the American Geophysical Union in Boston.

"The TRACE spacecraft is unique in that it has both high spatial and temporal resolution in the extreme ultraviolet, wavelengths of light that reveal the multimillion degree temperature of the Sun," said Dr. Alan Title, TRACE Principal Investigator from the Stanford Lockheed Institute for Scientific Research (SLISR) in Palo Alto, CA. "We can image solar activity in finer detail than existing spacecraft, and we can take a new image once every few seconds. Both are necessary for our mission, which is to understand in great detail how energy is transported from the solar surface into the outer atmosphere. In the past, spacecraft of lower resolution were forced to average over much larger areas and periods of time. This made it difficult to get at the fundamental physics."

"In our magnetic reconnection movie, we can distinguish the fine details of the magnetic fields and see how they change during time periods of about a minute. TRACE has given us many surprises, and new ones occur nearly every observation. We found that even large areas of the Sun, some more than 60,000 miles long, can heat up or cool down significantly and thus appear and disappear in just a few minutes," said Title.

The TRACE spacecraft, launched from Vandenberg AFB, CA, on April 1, 1998, joins a multinational fleet of International Solar Terrestrial Physics project spacecraft studying the Sun during a critical period when solar activity is beginning its rise to a peak early in the new millennium. The Sun goes through an 11-year cycle from a period of numerous intense storms and sunspots to a period of relative calm and then back again. The coming months in the Sun's cycle will provide solar scientists with periods of intense solar activity interspersed with periods when the Sun is relatively passive and quiet. This will give TRACE the chance to study the full range of solar conditions, even in its relatively short planned lifetime.

TRACE is training its powerful telescope on the so-called "transition region" of the Sun's atmosphere, a dynamic region between the relatively cool surface and lower atmosphere regions of the Sun (about 10,000 degrees Fahrenheit) and the extremely hot upper atmosphere called the corona (up to three million degrees Fahrenheit). Using portions of the telescope sensitive to extreme-ultraviolet and ultraviolet wavelengths of light, TRACE is studying the detailed connections between the fine-scale surface features and the overlying, changing atmospheric structures of hot, electrically charged gas called plasma. The surface features and atmospheric structures are linked by fine-scale solar magnetic fields. The solar atmosphere is constantly evolving because the magnetic fields that dominate the corona are continuously displaced by the convective motions in the outer layers of the Sun just below the photosphere.

The TRACE science team also will study the evolution of events, such as massive flarings and huge eruptions, in the Sun's atmosphere. These events originate at the Sun's visible surface, the photosphere, and travel upward through its atmosphere (chromosphere and transition region), and then into its super-hot corona before speeding out into space, sometimes towards Earth.

The power of the TRACE telescope to do detailed studies of the solar atmosphere makes this observatory unique among the current group of spacecraft studying the Sun. The spacecraft has roughly 10 times the temporal resolution and five times the spatial resolution of previously launched solar spacecraft. A Sun-synchronous orbit is uninterrupted by Earth's shadow for eight months at a time, allowing the mission the greatest chance to observe the random processes which lead to flares and massive eruptions in the Sun's atmosphere.

The TRACE core team consists scientists from Lockheed Martin Advanced Technology Center, Stanford University, NASA's Goddard Space Flight Center, the University of Chicago, Montana State University, and the Harvard-Smithsonian Center for Astrophysics. Images to support this story are available at:


Yohkoh "Science Nugget" Webpage

From SXT Chief Observer 14 Dec 1998

The SXT team would like to invite the solar physics community, as well as the public, to visit our "Weekly Science Nugget" Web page, which is located at . Each week a bite-sized piece of science or some interesting (and usually recent) observation using Yohkoh data is served up with images and text. (You may have already seen some of them as entries at the "APOD" site, There is a link to the archive of previous nuggets, which extends back to October 1997. Beyond serving as seeds for scientific research and collaborations, we hope that some of the science nuggets might also contribute as a useful educational resource for communicating the scope and wonder of solar science and astronomy to different sectors of the public (e.g., students, journalists, legislators, etc.). The nuggets tend to be technically a little bit higher-level than our YPOP pages.

Also the 150-foot tower at Mt. Wilson has a web site at:

And if you want to see if it's clear on Mt. Wilson, check the towercam on the 150-foot tower at:

From Solar News, The Electronic Newsletter of the Solar Physics Division American Astronomical Society, Volume 1999 Number 15:

The 60' Solar Tower, at Mt. Wilson Observatory now provides current solar images to the internet community. Daily GIF images are provided every clear morning at:

Daily images include a filtergram, dopplergram, velocity map, and magnetogram in the chromospheric sodium D-line region of the solar atmosphere. All GIF images can be viewed at 256x256, 512x512, and 1024x1024 pixel resolution. The original 1024x1024 fits images, from which the gif images are processed, are also included.

Past images can be searched for at;

Magnetograms from 1998 have been included, and previous year's magnetograms may be added as time or demand permits.

The 60' Tower continues to acquire two 1024x1024 pixel filtergrams each minute for up to 12 hours per day. From each pair of filtergrams a full- disk dopplergram is computed later. Plots of daily hours of filtergram observations, lists of temporal coverage of computed dopplergrams, and lists of temporal coverage of multi-day time series and power spectra will be provided online in the near future.

The following links are also relevant:

Homepage for IAU Working Group on Eclipses
Lockheed master list of solar web sites
Solar Probe Web site
New San Fernando Observatory Web Site
Yohkoh Outreach Site
TRACE Homepage
American Astronomical Society
The Solar Data Analysis Center at Goddard Space Flight Center The National Solar Observatory
The Space Environment Laboratory NASA Marshall Space Flight Center Solar Physics Branch "The Exploration of the Magnetosphere"
The Ulysses Mission Home Page
Home Page of the CfA Solar & Stellar X-ray Group
SoHO Observatory Home Page Sunspot Number and Butterfly Diagram
GONG (Global Oscillations Network Group)
The Nine Planets -- background information, photos & mirror sites
NOAA Solar Observations Homepage
NASA Space Physics Division
Miscellaneous Solar Images
Solar and Upper Atmospheric Data ServicesSunspot Index Data Center
Daily Sunspot and Magnetic Data from Mt. Wilson
NASA 1998 total solar eclipse bulletin
NASA 1999 total solar eclipse bulletin
Phil Harrington's Eclipse Home Page
Coronal data collected during the 1970's by the Skylab coronagraph
Mauna Loa Solar Observatory (Hawaii) Data Analysis Home Page
Mauna Loa Solar Observatory CME Events Home Page
Solar Maximum Mission Coronagraph [1980, 1984-1989] CME Events Home Page

Williams Astronomy and Astrophysics