Note: Information about the 1995,1996, and 1997 eclipse observations appear in Chapter 6.
The Solar Physics group at Stanford is pleased to announce the release of the
Stanford SOLAR Center
an educational web site providing solar on-line activities to encourage and share the wonder of solar science exploration.
Designed for grades 4-12, as well as interested adults, the site offers a multidisciplinary, hands-on approach to exploring the Sun. Data are provided by the SOHO spacecraft and, particularly, the MDI instrument from the Solar Oscillations Investigation team. To support and encourage the thematic approach, we've included solar art, folklore, and even ancient solar astronomy.
A WWW version of the Solar Lab used by the Astronomy 102 course at Williams College is under construction and will be completed shortly. <\p>
A SoHO Gallery of images from the Solar and Heliospheric Observatory is available.
White-light solar images are available on the Web. The RISE-PSPT (Precision Solar Photometric Telescope) is operating at the Astronomical Observatory of Rome with full disk images of the Sun, 1024x1024, in the blue continuum and in the Ca II K line. The daily sunspot drawings and magnetic polarities from the 150-foot Solar Tower of the Mount Wilson Observatory are posted. Go to the "Sunspot Drawing" link.
A set of four identical satellites from the European Space Agency to study the solar wind, known jointly as Cluster, were on board the launch of the first Ariane 5 rocket whose launch was aborted shortly after takeoff in early June. These satellites were to fly in formation around the Earth, giving uniform measurements of the solar wind from different locations in space. The rocket and its contents were destroyed.
The Sunspot Index Data Center at the Royal Observatory of Belgium, which keeps the International Sunspot number, lists daily sunspot numbers, yearly numbers, and so on.
A particularly spectacular color image with Comet Hyakutake B2 (C/1996 B2) near the sun, which is giving off a huge Coronal Mass Ejection, has been released.
A press conference on May 2, 1996, revealed the first scientific results from SoHO, including many images. Movies are also available.
The sunspot number and butterfly diagram, regularly updated, are available from NASA's Marshall Space Flight Center.
The Global Oscillation Network Group (GONG) went on line with all six sites on October 5, 1995. The sites, scattered in longitude around the world to provide uninterrupted coverage of the sun, are at Big Bear Solar Observatory, California; Mauna Loa, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; El Teide Observatory, Canary Islands; and Cerro Tololo Inter-American Observatory, Chile. Already, a 15-day continuous run has been obtained.
If you are interested in solar physics in general, visit NOAO. The National Solar Observatory, a separate listing for the Sacramento Peak Observatory, the GONG Project, and some solar eclipse pictures are available on the National Optical Astronomy Observatories' homepage.
The Solar and Heliospheric Observatory (SoHO) was launched by the European Space Agency on December 2, 1995. It carries 12 instruments to study the sun, from its core to its outermost atmosphere. The project is a collaboration between ESA and NASA.
Among the instruments is one for helioseismology. It will be of great interest to compare the SoHO results on this subject with those from the GONG project.
A coronagraph named LASCO was built by a consortium including the U.S. Naval Research Laboratory and laboratories in England, France, and Germany. It contains a set of nested coronagraphs covering regions of the corona at different distances from the sun, with different sensivity and resolution for each region. The artificial eclipses generated by these coronagraphs do not meet the standard of natural solar eclipses for resolution, but do provide continuity.
Still other instruments are sampling the solar wind as it flows by the spacecraft, studying the ions in it directly. And another instrument is studying the distribution of hydrogen in the heliosphere. it is studying Lyman-alpha ultraviolet light scattered by interplnaetary hydrogen atoms.
SoHO is observing the sun from the L1 Lagrangian point in space, a point where the gravity of the Earth and Sun balance. It is in a "halo orbit" around this point, which is to say that if we look out at the L1 point, we would find the spacecraft orbiting it in a small circle that resembles a halo. From this halo orbit, the sun is always visible, so the spacecraft is spared the hiding of the sun that happens for spacecraft in orbit around the Earth. Because its launch was so accurate, enough fuel remains on board to keep it in its position for 20 years, far longer than the original planned 6 years. A press release and list of experiments is available.
(related to Section 23.9 The Solar Wind pp. 409-10) Over the course of its five-year journey over both the solar poles, the Ulysses spacecraft confirmed some theories about the Sun and found a few surprises:
With its northern pass completed, Ulysses will begin to journey back out to the orbit of Jupiter. The spacecraft will reach the giant planet's distance of 5.4 astronomical units (about 800 million kilometers or 500 million miles) on April 17, 1998. Once there Ulysses will loop back and return, this time arriving in the vicinity of the Sun during its most active sunspot phase.
"The Sun will be near solar maximum in the fall of 2000 and the solar magnetic field will have reversed polarity," said Dr. Edward J. Smith, Ulysses project scientist at JPL. "We expect the profile we obtain five years from now will be dramatically different and give us many new insights into the dynamics of this star at the center of our solar system."
Based on the importance of its investigations and the excellent condition of the spacecraft, the Ulysses mission will continue through a second set of polar passes beginning in September 2000. At the conclusion of its mission in December 2001, the spacecraft will have collected data on solar phenomena at all latitudes during the quietest and most active phases of the 11-year solar cycle.
[From a NASA press release, 11/1/95]
(related to p. 391 Section 23.2b: Solar Seismology) The Global Oscillation Network Group (GONG) project got onder way in September 1995, with the deployment of six stations in California, Hawaii, Australia, India, the Canary Islands and Chile. Already in the first month of operation, a 14-day run of continuous observations of the sun was obtained. The first set of data should be reduced by springtime; it will reveal information about the inside of the sun. The SoHo spacecraft should be launched by then.
A very nice site including all kinds of information about the sun, including descriptions and photographs of many types of solar phenomena, is available on the World Wide Web. It was assembled by Bill Arnett of San Jose, CA, as part of his Nine Planets site.
Students for Exploration and Development of Space have a Web site with lots of solar images and movies.
NASA's Solar Data Analysis Center has images in a variety of wavelengths and links to solar missions (including SoHO and the coronagraph on the SPARTAN 201 mission that flew in 1995).
Updates to the "solar constant" graph (Fig. 23-46), more properly now known as the "solar irradiance," are made by the National Scientific Data Center.
In Figure 23-46B in the 1995 Version of the text, the yellow curves were printed reversed from right to left. Also, the label "inverted" on the sunspot-number curve should be deleted.