Stellar scintillation

Stellar scintillation

Aboriginal and Torres Strait Islander people developed extensive knowledge about the world around them through observation, experimentation, experience, and deduction.

Just like art and music, science is an integral part of Indigenous cultures around the world, including Australia. In this module, teachers and students will learn ways Aboriginal and Torres Strait Islander people observe the twinkling of stars to predict weather and seasonal change. Students will learn the science of scintillation (twinkling) and see how Aboriginal and Torres Strait Islander understood and utilised this principle long ago.

Scintillation

Torres Strait Islanders carefully observe the different ways the stars twinkle, including their speed, any colour changes, and sharpness of stars.1 This is utilised to predict changes in the weather and foretell seasonal change. On Mer (Murray Island) in the eastern Torres Strait, the people closely observe the stars. If they twinkle rapidly, the observer can forecast weather and wind speeds. In scientific terms, scintillation (twinkling) is caused by refraction of starlight as it travels through columns and layers of moving air in our atmosphere - each layer having differing temperatures, densities, and speeds (Fig. 1). This is turbulence. High turbulence from hot, fast winds result in very rapid twinkling stars, whereas stars visible in cooler, calmer conditions shine with a relatively steady light.


Fig. 1 (Left): cause of scintillation. Image: Enchanted Learning: www.enchantedlearning.com. (Right): Effect of altitude on thickness of atmosphere. Image: Bob King, Sky & Telescope.

Meriam elders say they watch the “top stars” (high altitude stars) to get the most accurate reading. Due to the curvature of the Earth the relative thickness of the atmosphere differs depending on the angle of altitude. When looking towards the horizon (low altitude), the layer of atmosphere from our viewpoint is much thicker. Therefore, more starlight is refracted and absorbed than for observations directly overhead (high altitude, reaching a peak at zenith – the point directly above our heads). For this reason, bright stars at high altitudes (shining through the equivalent of one-atmosphere thickness) are better indicators for weather forecasting than those close to the horizon. On the horizon, starlight must pass through the atmosphere that is about 30 times thicker than the atmosphere when looking at zenith (straight up).

Elders explain that Meriam people also look for colour changes in bright stars as they twinkle. Normally red stars appearing bluish in colour indicate humidity. If the stars are twinkling rapidly, appear blue, and look fuzzy, they know a storm is approaching. Elders explain that blue twinkling stars that do not change colour indicate clear, hot weather. This is common during the Nay Gay (hot/humid) season from October to December. Stars twinkling rapidly but appearing blue in colour indicate approaching storms that are common in the Kuki (monsoon) season from January to April. Near the boundary of these seasons (December), Islanders watch for rapidly twinkling stars when ground conditions are pretty still. This is a sign of the changing trade winds, shifting from the cooler south-easterlies to the hot, wet north-westerlies.

Changing colours of stars, as well as them looking fuzzy, is evidence of Meriam science in action. These properties inform observers about the conditions of the local atmosphere. Water vapour absorbs light in the red/infrared end of the colour spectrum (Fig. 2). As a consequence, as atmospheric moisture and humidity increases, red-orange stars tend to lose their ruddy colour and appear more bluish-white.


Fig. 2: Absorption of light by water. This shows red and green light is significantly absorbed by water, while blue light is barely absorbed. Image: Wiki commons license

Another effect of high atmospheric moisture and humidity is that stars tend to look more diffuse rather than sharp pinpoints of light, as is the case in very dry air. This effect is seen more readily in the fainter stars, especially along the band of the Milky Way. Some astronomers give it the term “Vaseline Sky”, as it is just like trying to look at the stars through glass smeared with a thin layer of Vaseline.

For Meriam people, these observations inform fishing practices. Elders explain that “when the stars ‘twinkle hard’ (rapidly) and the wind drops”, this is a good time to go fishing. If fishermen are out on the reefs, they can read the stars to know if they are safe to travel back home.

Islanders also note that not all the stars in the sky twinkle. Some of those are not stars, but rather planets. Because the planets are much closer than the stars, the sunlight reflected from them is not severely affected by our atmosphere. This was one of the ways Islanders distinguished planets from stars, which they called “epreki2.

Similar scientific principles are found in Wardaman Aboriginal traditions of the Northern Territory. Uncle Bill Yidumduma Harney explains that Wardaman people predict the wet season (from October to April) by looking for the bright twinkling of of the star Canopus (Ngilmungngilmung) in the dawn skies of September3.


Classroom activity - Science Year 8

This activity involves watching a video of an elder playing a Meriam star song and learning about the scientific information it describes. It will help students learn how scientific information is developed in situ from the local environment and ecology. Students will hear the song, learn the translation, and describe the scientific information it describes by examining weather patterns in the Torres Strait and how twinkling stars are used to predict this seasonal change. The song Wer Naskaisreda (The Twinkling Stars) was originally composed by Meriam man George Passi in the 1960s, and is a more contemporary song. It is sung in the Meriam Mir language. This activity builds on what students learned in the Year 5 English module on Indigenous astronomy, in which they learn about a traditional sacred kab kar dance from the Torres Strait.

Curriculum connections

This addresses the following content descriptions from the Australian Curriculum:

  • People use science understanding and skills in their occupations and these have influenced the development of practices in areas of human activity (ACSHE136)
  • Identify questions and problems that can be investigated scientifically and make predictions based on scientific knowledge (ACSIS139)

This resource addresses the following excerpts from the achievement standard for Year 8 in Science:

  • explain how evidence has led to an improved understanding of a scientific idea and describe situations in which scientists collaborated to generate solutions to contemporary problems
  • reflect on implications of these solutions for different groups in society
  • identify and construct questions and problems that they can investigate scientifically
  • use appropriate language and representations to communicate science ideas, methods and findings in a range of text types

Inquiry-based learning questions

  • How did Aboriginal and Torres Strait Islander people develop scientific knowledge about the stars?
  • How is this knowledge encoded in oral tradition (including song)?
  • How does this knowledge apply to the local environment?
  • How do Torres Strait Islanders convey this knowledge to younger generations?

Activity 1 - Uier Naskaisreda (The Twinkling Stars) song

Suggested timing for activity: 45 mins

Required resources: computer, TV, pen, and paper

  1. Students will be shown a video of the Meriam elder Alo Tapim performing the song Uier Naskaisreda, meaning “The Twinkling Stars”.
  2. Students will read the lyrics of a Meriam song about the twinkling stars. The song is in the Meriam Mir language and translated into English. (ACSHE136)
  3. Student should study the lyrics and any scientific descriptions in the song. (ACSIS139)
  4. After the students are provided a hand out of the songs translation, they should highlight the major elements of the song with respect to science.
  5. Questions include “What is the seasonal change the song is describing?” “What time of year does it occur?” “What is the science behind the twinkling stars described in the song?” “How is this knowledge used for practical purposes?”
  6. For each of these questions, the students should take time to go online and look up climate information for Mer, as well as traditional seasons.4
  7. This information is then matched with the content at the start of this module to explore the scientific basis for this knowledge, which Islanders developed long ago - see below. (ACSHE136)
  8. How do Meriam people communicate these ideas to young people? (ACSIS139)

Wer Naskaisreda (The Twinkling Stars)

Song composed by George Passi. Lyrics provided by Segar Passi. Translated by Alo Tapim.

Why is it so calm tonight?[Why is it so quiet, without wind?]
Why are the stars twinkling...
Like sparks in a fire?

I think it's because of the big wind
The clouds are coming from the cold southwest
And being swept to the northwest
Why are the stars twinkling like sparks?

Teacher notes

This song describes seasonal change that occurs later in the year. In November and December, the air is very hot and still, but the skies are clear. The wind if often very lor or dead still, something the Islander call duldrum. They can see the stars rapidly twinkling above. This foretells a shift from the cooler, dryer season (Sager) dominated by southerly trade winds to the wet season (kuki), which is dominated by northwesterly trade winds. At this time of year, the winds are high altitude and are calmer at the ground level. These strong winds make the stars twinkle, hence the song.

Activity 2 - Observing Twinkling Stars

Suggested timing for activity: Up to student. Could take place over a period of days or weeks

Required resources: pen and journal

Teacher notes: This in an out-of-class experiment for students (ACSIS139)

  1. Students are to keep a notebook of observations of planets and stars in the sky on a few given nights.
  2. They should note if the stars and planets twinkle.
  3. If so, is the twinkling fast or slow? Do the stars appear sharp or fuzzy?
  4. Are the students able to distinguish between a planet and a star by observing if it twinkles?
  5. Are the planets twinkling? What was the weather that day, and the next?
  6. If the planet(s) twinkle, it it high in the sky or low on the horizon?
  7. A range of freely available astronomy-related mobile apps5 that can be used by the students to check and see if the “stars” they observed were actually stars or planets.
  8. The teacher can lead a discussion with the class about their results.

Teachers should know that if planets are close to the horizon, they may still twinkle. A Kamilaroi tradition from northern NSW tells about the planet Venus twinkling brightly when it is low on the horizon. The people see it as an old man who is laughing at a rude joke he told.6

Notes

1 Hamacher, D.W.; Barsa, J.; Passi, S.; and Tapim, A. (2019). Indigenous use of stellar scintillation to predict weather and seasonal change. Proceedings of the Royal Society of Victoria (in review)

2 Haddon, A.C. (1912) Cambridge Anthropological Expedition to Torres Straits, Vol. IV. Cambridge University Press, Cambridge.

3 Cairns, H.C. and Harney, B.Y. (2003) Dark Sparklers. Merimbula, NSW: Hugh Cairns. pp. 142, 207.

https://www.qcaa.qld.edu.au/about/k-12-policies/aboriginal-torres-strait-islander-perspectives/resources/seasons-star

https://www.hongkiat.com/blog/stargazing-apps/

6 Mathews, J. (1981) Fossils & families: Aboriginal life and craft. Sydney, Collins.

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The development of these resources was funded through an Australian Government initiative delivered by the University of Melbourne's Indigenous Studies Unit. The resources include the views, opinions and representations of third parties, and do not represent the views of the Australian Government. They have been developed as a proof of concept to progress the inclusion of Aboriginal and Torres Strait Islander content in Australian classrooms. In drawing on the material, users should consider the relevance and suitability to their particular circumstances and purposes.