Great Britain covered by snow

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Caption: Snow covering almost all of Great Britain. This image was taken by the MODIS instrument on NASA's Terra satellite on the 7th of January 2010. On most days in winter only the highest mountains in Great Britain will be covered in snow. But a very cold weather and heavy snowfall in early January 2010 led to all but a few areas on the coast being covered by snow. Ireland on the left is mostly covered by cloud, but where there are gaps we can see no snow coverage.
Credit: NASA image by Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center
Credit Link

Glossary Terms: Winter

License: Public Domain Public Domain icons

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Luminous Salar de Uyuni

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Created for the OAE

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This black and white image taken in February 2017 in Uyuni Salt Flat of southwest Bolivia, the biggest salt flat in the world, shows one of the most recognisable constellations, Orion the hunter, and the open star cluster of the Hyades directly above the clouds at the horizon. Various cultures have different stories associated with Orion. The Aymara in this area of the world (Bolivia and Northern Chile) consider Orion’s Belt to be a Sky Bridge (chacka cilitu) or a Stairway made out of dough. This stairway is rather obvious in this picture. It appears as if the stars in the sky are scattered like grains of salt on the ground — an amazing composition. For the Aymara, who were Christianised by the Spanish conquistadores, Orion and the Stairway are connected to the November festivals of the dead ancestors and the souls. In contrast to the original Christian culture, for these people in the southern hemisphere these festivals mark the beginning of summer, not the beginning of winter. While in the north, the “ghosts” of the ancestors are represented by the foggy weather in November, the Aymara greet the ancestors with flowers. This photograph in the dry salt flat, in contrast, seems to show the unlivable loneliness where the photographer meets the souls of the deceased. The Yolnu people of Arnhem Land in Australia’s Northern Territory have a rich culturally significant story associated with Orion that carries a lesson. It tells of the three brothers of the Kingfish clan and their canoe Djulpan. Owing to their lack of patience, the brothers ate the sacred Kingfish, angering the Sun woman Walu who created a waterspout that sent them into the sky. Looking at the constellation Orion, the three stars in Orion’s belt represent the three brothers, Orion’s sword is the fishing line, and the two dimmer stars Bellatrix and Saiph form the two ends of the canoe Djulpan.
Credit: Stephanie Ye Ziyi/IAU OAE

Glossary Terms: Constellation , Orion
Categories: Naked Eye Astronomy , Stars

License: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons

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Apparatus for determining the gravitional constant

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Caption: Observations of the motions of the planets around the Sun, or the Moon around the Earth, could not yield the gravitational constant, as in those cases, the mass of the central body is not initially known. Measuring the gravitational constant required a situation where the masses involved had been determined independent of measuring their gravitational attraction. The device shown here was built by John Michell (1724–1793), but Michell died before he could perform the experiment. Henry Cavendish (1731–1810) inherited the device, modified it so as to suppress external disturbances, and successfully completed the experiment. Cavendish's report to the Royal Society was under the title of "Experiments to determine the density of the Earth" as, from knowledge of the gravitational constant, the gravitational acceleration at Earth's surface and the Earth's radius, one can determine the Earth's mass and its mean density. From the modern perspective, what is now known as the "Cavendish experiment" is seen as a way of determining Newton's gravitational constant G. The image shows a cross-section of the apparatus, which Cavendish had further isolated from environmental influences by putting it into a separate room and inside a wooden box. The devices allowing Cavendish to illuminate, observe and manipulate the experiment from the outside are pictured as well. The core of the experiment is a torsion balance using two small lead spheres. The restoring force of the torsion pendulum is deduced from its natural oscillation frequency in the absence of the large masses. The gravitational attraction of the small lead spheres to their larger counterparts can then be determined by measuring how far it makes the torsion pendulum masses deviate from their null position. The image is a slightly modified (cropped, contrast and brightness adjusted) version of Fig. 1 in Cavendish's article in the Philosophical Transactions of the Royal Society, Volume 88 (December 1798), pp. 469–526 [DOI: 10.1098/rstl.1798.0022]. The permission of the Royal Society to publish this image under a CC BY licenses gratefully acknowledged.
Credit: Henry Cavendish in Philosophical Transactions of the Royal Society, DOI: 10.1098/rstl.1798.0022
Credit Link

Glossary Terms: Gravitational Constant , Gravity
Categories: Physics

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To guard the Stars and the Sea Together

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Created for the OAE

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns. This image composition is amazing. In the far background of the landscape we see a chain of mountains that seems to mirror the structure of the Milky Way in the sky above. The strong daylight-like colours of the landscape are caused by the Moon, the bright light at the top of the image. Taken in Kinabalu, Malaysia, in February 2019, this image shows the alignment of planets and the Moon, conveying the idea of the ecliptic as the central line of the Zodiac, the plane within which all planets orbit the Sun. The ecliptic is the central line of the Zodiac, so the region of about five to 10 degrees either side of the ecliptic is where the constellations of the Zodiac are located. Starting from the horizon towards the bottom left of the image we can see the planets Venus, Saturn and Jupiter. The planets have different cultural significance for people around the world, and are deeply embedded in social, religious and practical aspects of life. For example, Wardaman traditions of Indigenous Australians associate the planets with ancestor spirits who traverse the Celestial Road (ecliptic). The appearance and disappearance of planets in the sky are associated with various ceremonies. For example, when Venus starts being the “Morning star” after having been the “Evening star”, this marks the Banumbirr ceremony for the Yolnu people of Arnhem Land, in Australia. The image also shows the constellations Scorpius, Aquila, Lupus and Triangulum Australe, the asterism of the Teapot, and the two pointer stars Alpha and Beta Centauri. The constellations, asterisms and individual stars within them have significance in many different cultures. Malaysia, being close to the equator, has had connections to the north as well as to the south and almost the whole sky is visible over the course of the year. The star Antares is seen by the Kokatha people of the Western Desert as Kogolongo, the red tailed black cockatoo, while the Boorong refer to it as Djuit, the red-rumped parrot. The two stars which form the stinger of Scorpius (Shaula and Lesath), are called Karik Karik, the Australian Kestrel.
Credit: Likai Lin/IAU OAE

Glossary Terms: Constellation , Jupiter , Moon , Saturn , Scorpius , Venus , Zodiac , Asterism , Alpha Centauri
Categories: Naked Eye Astronomy

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Milky Way Arch over Lut Desert, Iran, by Amirreza Kamkar, Iran (Islamic Republic of)

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Created for the OAE

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Wide star fields. This panoramic dawn image shows the majestic band of the Milky Way – our home Galaxy – made up of a few hundred billion stars, among other structures, most of which are not detectable by our eyes, or in some cases even directly with telescopes. The appearance of the band is because the Milky Way is a disc-shaped galaxy, and we (Earth/Solar System) are situated within the disc. Diverse cultures and traditions around the world each have their own name and cultural stories for the Milky Way. The dark regions visible in the Milky Way are large, dense, cool nebulae (clouds of dust and gas), which obscure the light from stars in the Milky Way. The Indigenous Australians associate stories with the dark patches of the Milky Way, one of the most prominent being the Emu in the Sky (called Tchingal in Wotjobaluk country). In and around the band of the Milky Way there are a vast range of star clusters, two familiar ones are M6 (Butterfly cluster) and M7 (Ptolemy’s cluster). The bright point just above the horizon is the planet Venus (known to the Boorong people of Indigenous Australia as Chargee Gnowee, elder sister of the Sun). Within the band of the Milky Way the brightest point in the image is the planet Jupiter (called Ginabongbearp, the Sulphur-crested white cockatoo by the Boorong). The planet Saturn is the bright point between Venus and Jupiter (closer to Venus than Jupiter). There are two constellations and one asterism that can be easily discerned in the image: Aquila, Scorpio (Maui’s Hook), and Teapot (asterism in Sagittarius). In this image, the center of the Milky Way at an approximate distance of 26,000 light years from Earth, is located roughly to the top right of the Teapot spout. The bright red-orange point to the right of Jupiter is the red supergiant star Antares and is part of the constellation Scorpio (known as Maui’s Hook in Māori and Polynesian cultures). This variation in the colour of stars is the result of temperature of the stars (lower temperature stars are redder, higher temperatures stars are bluer).
Credit: Amirreza Kamkar/IAU OAE

Glossary Terms: Milky Way , Dust Cloud
Categories: Milky Way and Interstellar Medium , Naked Eye Astronomy

License: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons

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