What do Stonehenge, Mayan pyramids, and a spacecraft a million miles away have in common? They’re linked by a human need to explore and understand the Sun, moon, planets, and stars.
Image to right: A Snapshot of the Sun: This up-to-date solar movie is from SOHO (Solar and Heliospheric Observatory), a NASA-European Space Agency satellite. Click on image for movie (no audio–1.3 MB.) Credit: NASA/ESA
This year’s Sun-Earth Day on March 20 focuses on “Ancient Observatories: Timeless Knowledge” and falls on the vernal equinox when day and night are the same length. Appropriately, NASA and the Exploratorium in San Francisco are focusing on ancient peoples and their fascination with the Sun, which played a major role in most Native American religious practices and social events.
NASA continues to pay close attention to the Sun today through ground and satellite-based observatories, still seeking to understand this star as a dominant influence on our lives. The Sun seems to have a major role not only in religious practices of indigenous people, but also art, culture, and more.
Image: Hovenweep National Monument: This spectacular sunset was taken during the 2004 summer solstice at Hovenweep National Monument (HNM). Hovenweep National Monument protects five prehistoric, Puebloan-era villages spread over a twenty-mile expanse of mesa tops and canyons along the Utah-Colorado border. The “sun room” a rectangular room attached to southern side of this tower could have been used to mark the equinoxes and solstices. Beams of light shine through portholes illuminating lintels on doorways in the room. Credit: Troy Cline
For example, the Mayans built the Pyramid of Kulkulkan in El Castillo, Mexico between 1000 and 1200 A.D. with the Sun’s movement in mind. Located in the ruins of Chichen Itza, this 75 foot-tall, squared based pyramid is unique among all known pyramids worldwide for its central role in a dramatic shadow and light display during the spring and fall equinoxes. The axes that run through the northwest and southwest corners of the pyramid are oriented toward the rising point of the Sun at the summer solstice and its setting point at the winter solstice. Kukulcan is the Mayan name for the Feathered Serpent God (also known as Quetzalcoatl to the Aztecs).
Image to right: Brochure–Ancient Observatories, Timeless Knowledge: Download the official Sun-Earth Day brochure and explore ancient and modern observatories throughout the world. Credit: NASA
In Chaco Canyon, located in the Chaco Culture National Historic Park, N.M., several structures indicate the ancient culture’s understanding of the Sun’s movements. Pueblo Bonito’s special corner windows let sunlight through, but only as time marches onwards to the winter or summer solstice. At Casa Rinconada, a window on the south wall lets a beam of light shine into a niche on the back wall at the time of the summer solstice. Fajada Bute projects a dazzling “Sun Dagger,” where during equinoxes and solstices, one or sometimes two, thin slivers of light frame a spiral petroglyph.
Across the globe to ancient Egyptians, the Sun God Ra was the most universally worshipped king of the gods and all-father of creation. He commanded a chariot that rode across the sky during the day. The magnificent temple at Karnak celebrates Ra through its enormous pillars, designed in harmony with the Sun and stars over a span of nearly 2000 years.
Image: Sun-Earth Day Site: Play the part of archaeologist on this companion Sun-Earth Day site that uses satellite images, photographs, and historical records to provide a timeline for two ancient observatories. Credit: NASA/Ideum
We may never know for certain just how these solar-inspired structures were used. There also remains some controversy about their exact details and the actual intent of their creators. But we can at least admire their creators for what must have been a sophisticated understanding of the Sun’s movements. We can also admire them for their cleverness in applying this knowledge to enhance their own survival in a largely unforgiving environment.
The purpose of Sun-Earth Day is to get people to understand that the Sun is a magnetic star that impacts the Earth and other planets in our solar system, and that humans of all cultures and times have and will use technology to understand the Sun and the Universe beyond.
Image: STEREO animation: STEREO is the next big solar mission set to launch in 2006. Two nearly identical spacecraft will image the Sun and its massive explosions in 3-D for the first time ever. Credit: NASA/Chris Meaney. Image below: The animation shows how Earth’s tilted orbit around the Sun creates the different seasons we experience. Day and night are the same length on the vernal equinox, March 20. This year marks the sixth Sun-Earth Day, which falls on or near the equinox (no audio–13 MB). Credit: NASA/Walt Feimer. 
The latest about the webcast from Chichen Itza:
English Educational Program
5pm EST, 4pm Mexico, 2pm PST
Observations of solar alignment – Bilingual in English and Spanish
5:45pm EST, 4:45pm Mexico, 2:45pm PST
Spanish Educational Program
6pm EST, 5pm Mexico, 3pm PST
Governor of Yucatan addressing museum audience after Spanish webcast
After the end of the Spanish webcast program, at approximately 3:50-4:10pm PST on Sunday, March 20th, there will be a short segment of webcast featuring the governor of Yucatan, two city mayors, and a group of local children from the Chichen Itza area. This is part of a community outreach program in the San Francisco area and our guests will be addressing the webcast audience attending the Exploratorium event. However, this segment will be available for the general national audience via the same internet and satellite access for the Sun-Earth Day webcast program. Please feel free to view this segment during your event if you find it relevant to your scheduled activities.
For more information about Sun-Earth Day, please visit on the Internet:
http://sunearthday.nasa.gov
En Espanol por favor visite en el Internet: https://www.nasa.gov/vision/universe/solarsystem/sun_earthday_spanish.html
Rachel Weintraub
Goddard Space Flight Center