Astronomy

Learning intentions:

We will learn of western astronomy via an examination of James Cook’s observations of the transit of Venus in 1769, as well as the astronomy of the Aboriginal and Torres Strait Islander peoples. We will look at the differences and the similarities between the two ways of looking at the night sky.

About the activity

Students will:

learn about the transit of Venus
explore the technology used by Europeans at the time of the Endeavour voyage to observe the transit of Venus in 1769
compare observations of the night sky made by Aboriginal peoples and Europeans at the time of the Endeavour voyage
explore the use of astronomy by Aboriginal peoples and Europeans to navigate at the time of the Endeavour voyage.

Learning intention

We are comparing and contrasting ways of observing the night sky and how these observations aid navigation.

Inquiry questions

Why was it important to observe the transit of Venus across the Sun?
How are the observations of the night sky made by Aboriginal peoples different from those made by Europeans at the time of Endeavour voyage?
What is the role of astronomy in navigation?

Engage: the transit of Venus

Why was it important to observe the transit of Venus in 1769?

Setting off for Tahiti

Lieutenant James Cook set sail from England in the Endeavour in 1768 on a special scientific mission. His job was to travel to Tahiti to observe and record the transit of Venus predicted to occur in June 1769. On board the Endeavour was the astronomer Charles Green, but James Cook himself was highly competent in basic astronomical observation. Cook had been provided with everything he and Charles Green would need to successfully do the job—telescopes, an astronomical quadrant, watches to keep time and various other items.

Why Tahiti?

The island of Tahiti had been visited by the English explorer Samuel Wallis in June 1767, the first European to do so. British scientists realised it was important to observe the transit from widely separated places on the Earth, and since the location of Tahiti was now known, it became an ideal location to observe the transit far from Europe.

Why a transit of Venus?

Scientists of the time thought that by carefully observing a transit of Venus they could work out how far the Earth and Sun are apart. This distance is called an astronomical unit [AU], which we now know to be roughly 150 million kilometres. The observations would need to be carried out from various different places on the Earth's surface, and the results compared.

What was James Cook’s most important task in Tahiti?

When the day came, 3 June 1769, the only task Cook really needed to make sure of was to accurately record how long it took for the transit to occur from beginning to end. In other words, he needed to record how long it took for the small black outline of Venus to completely cross the face of the Sun. So it was critical to be watching for when the very first hint of the outline of Venus touched the edge of the Sun, and then to continue observing until the very last part of the outline of Venus moved away from the face of the Sun, and to keep track of the time as it progressed.

Recording the transit

Just in case there were clouds in the sky on 3 June 1769, James Cook organised for two other groups to be doing the same thing at other locations around the island of Tahiti. All three groups were successful.

Source 1 shows the sketches made by James Cook and Charles Green of the first part of the transit. Figure 1 on each set of sketches shows the first point of contact.

Source 2 shows the results that James Cook presented to the Royal Society when he returned to England. The first row, Contact 1, gives the time measured when the outline of Venus first touched the outline of the Sun. The second row, Contact 2, gives the time when the outline of Venus first completely entered the outline of the Sun.

The third row, Contact 3, gives the time when the outline of Venus first touched the outline of the Sun having crossed the face of the Sun, and the fourth row, Contact 4, gives the time when the outline of Venus finally left the outline of the Sun completely.

Source 2: Orchiston, Wayne (2004) James Cook's 1769 transit of Venus expedition to Tahiti. Proceedings of the International Astronomical Union. 2004. 52 - 66. 10.1017/S1743921305001262

The diagram is from a Science@NASA site, The 2012 Transit of Venus. Image credit: Science@NASA

Source 1: The sketches of the 1769 transit of Venus by James Cook and Charles Green in TahitiSource: NASA | Image scan provided by the Museum of the History of Science, Oxford. Originally published as part of ‘Observations Made, by Appointment of the Royal Society, at King George’s Island in the South Sea; By Mr. Charles Green, Formerly Assistant at the Royal Observatory at Greenwich, and Lieut. James Cook, of His Majesty’s Ship the Endeavour’, in Philosophical Transactions, 61 (1771), 397-421. | Public domain

The calculations

It was these readings of the times taken for the four different stages of transit to occur that were so important to measure. In other parts of the world the same thing was done, but because the view of the transit was different from different parts of the world, and the path across the sun appeared either longer or shorter, the time taken for the transit would be different. It was precisely these differences that would allow astronomers to do the very tricky calculations that would eventually allow them to calculate a figure for the distance to the sun, something they were desperate to learn.

Making sure of the latitude and longitude

One other critically important thing was to have accurate measurements the latitude and longitude of the location where the observations were made—without those, the time measurements would be useless no matter how carefully they were recorded. Charles Green was an expert at calculating latitude and longitude, so there was no problem there.

The final calculations

Based on his analysis of the 1769 transit of Venus, the British astronomer Thomas Hornsby wrote in 1771 that '... if the semidiameter [the radius] of the Earth be supposed = 3985 English miles, the mean distance of the Earth from the Sun will be 93,726,900 English miles.'

This figure is equivalent to 150 838 800 km (nearest 100km) which, when compared to the modern figure for the average distance from the Earth to the Sun of 149 597 900 km, shows an error in the 1769 figure of less than 1% - a remarkable achievement.

Looking further

You can find out more about transits of Venus, how these allow us to calculate the value of one astronomical unit (AU), and why this is important at this Exploratorium site.

Astronomical quadrant

Source 3 is an astronomical quadrant (circa 1760), a piece of navigation equipment that was used to measure the angle of a celestial object (a star, a planet, the Sun or the Moon) from the point immediately overhead (the zenith). An astronomical quadrant similar to the one pictured was used by James Cook and Charles Green in Tahiti to assist in the calculation of the latitude and longitude where the transit observations were made, at a place Cook named ‘Point Venus’. While at sea, Cook and Green frequently calculated the Endeavour’s latitude and longitude using their own portable quadrants to make the required readings. Find out more at a NASA Science page, James Cook and the Transit of Venus.

Activity - transit of Venus

Notice that in Source 2 that Cook, Green and Solander recorded different timings for the start of the transit. Propose reasons for these difference and describe the evidence used to support your reasoning. (Keep in mind that each person was making his own independent observation using different telescopes from different sites).
Scientific advances rely on solid evidence, such as measurements and data such as the averages of multiple measurements. Make a judgement about the evidence provided by Cook and the other groups by completing the following:
1. Calculate the total time taken from contact 1 to contact 4 for each of the groups (Cook, Green and Solander).
2. Find the average total time.
3. Convert the average total time to seconds.
4. Calculate the difference (in seconds) between the largest and smallest measurements.

Source 3: 12 inch astronomical quadrant, about 1760. Exhibit from the National Museum of AustraliaFor more information visit: the National Museum of Australia.

Explore: Wurrum-Boorrool

'Aboriginal and Torres Strait Islander people were, and continue to be, careful observers of the stars. The stars are the homes of ancestors, animals, plants, and spirits. The stars serve as calendars, a law book, and inform all aspects of daily life and culture. The First Australians observed the properties of stars (such as brightness, colour, and position) and noticed even the most subtle changes in these properties. Ancestor spirits in the sky serve as a law book and mnemonic for the people to remember important life and social lessons.'

Australian Indigenous Astronomy [site accessed 22 June 2020]

Source 4 In this BBC video [1:09], Ghillar Michael Anderson, elder of the Euahlayi nation tells the story of the Wurrum-Boorrool, which you may know as the Milky Way. Transcript on Teacher notes page.

Activity: Exploring different views of the night sky

Watch the video, making notes about the information it presents.

Once you have watched the video, complete these tasks.

Record the Euahlayi names and the English names for the features of night sky discussed in the video.
Explain in your own words the significance of the river that Ghillar Michael Anderson describes seeing in the stars.
Describe the spiritual connection that Ghillar Michael Anderson feels to the tree he sees in the night sky.
Why do you think the makers of this video filmed Ghillar Michael Anderson in the setting you see in the video?

Explain: Stories in the stars

'Aboriginal people had a very practical reason for their interest in astronomy: the sky is a calendar that helped Aboriginal peoples predict when the seasons are shifting and when certain foods are available. It was also valuable spiritually, as a means of reinforcing culture and community, with constellations and patterns in the sky attached to stories, the landscape, navigation and also the values and morality of the community. So when constellations and patterns appeared, the stories were told and those lessons would be ingrained in the younger people.'

This explanation is from Australia's first astronomers, an ABC Science website (Source 8 on this page).

Activity

Watch Source 5 the TEDx talk by Kirsten Banks, and read the information available at Australia's first astronomers.
Describe how the Emu in the Sky changes its position and appearance at different times of the year and the implications for hunting and other activities for different Aboriginal groups.
Investigate ancient aboriginal knowledge of stars that change brightness and then use modern sources to investigate which stars may exhibit changing brightness. Evaluate the explanations of why the brightness appears to change.
research and construct a table that indicates the months, the locations of the Emu in the Sky and the significance of its' position to the Kamilaroi people. Use Source 6, Star Stories of the Dreaming, a study guide for K-10 students published by ABC Education and Maquarie University.

Source 5 is a TEDx talk is by Kirsten Banks, an Aboriginal woman of Wiradjuri ancestry and an astronomer. Transcript is available on the teacher notes page.

Source 6: Star Stories of the Dreaming, a study guide

Elaborate: The world's first astronomers?

Source 7 [2:22 mins] Ben Flick, an Aboriginal man from the Kamilaroi language group of north-western NSW, explains a creation story passed down to him regarding 'the emu in the sky''. Transcript is available on Teacher notes page.

Australia's first astronomers

Visit Source 8, Australia's first Astronomers, an ABC science website. You'll read an Emu in the Sky story from Papunya in the Northern Territory and learn about aspects of Aboriginal astronomy.

Activity

Compare and contrast the information presented in Source 6, 'Through Our Eyes' and Source 7 'Australia's first astronomers'.
Elaborate on the claim that Aboriginal People can be called the world's first astronomers.

Source 8: Australia's first astronomers published by ABC Science

Gugurmin – The Emu in the Sky

Source 9 is a short video with no commentary showing the unboxing of a 2020 coin minted by the Royal Austalian Mint. At 0:20 seconds, the base of the box is seen. This text is on the box:

'Aboriginal elders teach that everything on the land is reflected in the sky. One of the most widespread Aboriginal constellations across Australia is the great Emu in the Sky. Instead of a constellation of bright stars, it is a silhouette traced by the dark spaces in the Milky Way, stretching from the Southern Cross to Sagittarius.

In Wiradjuri traditions of central New South Wales, the celestial emu is Gugurmin. When Gugurmin rises at dusk in Bangalang (Autumn), the birds are nesting and it’s the season to collect their eggs for food. Male emus sit on the nests over Babang (Winter) and the chicks hatch in Yiraga (Spring), and are reared by the father emus. This coincides with coming-of-age ceremonies (Burbung), as represented by the young dancers.

Artist: Scott ‘Sauce’ Towney (Wiradjuri Artist, Peak Hill, NSW)

The Royal Australian Mint acknowledges the Ngunnawal People, traditional custodians of the land on which this coin was minted.'

Looking further

You can find out more about this topic by reading the online article Coins and constellations published by the University of Melbourne,

Source 9: Video [0:59 min] showing a coin minted by the Royal Australian Mint.

Activity

After reading all the information in this section 'Elaborate: The world's first astronomers?' create a presentation for your classmates about the Emu in the Sky or another feature in the night sky of your choice. This could take the form of:

a poster
a multimedia presentation
an illustrated talk
your own choice.

Evaluate: Taking the time to look up

The evening sky - many bright stars, with the Milky Way and Southern Cross seen, reflected in a still lake.

The Milky Way rises over Island Point in the Peel-Harvey estuary, Western Australia. Photo by Luke Busellato CC BY-SA 4.0

Activity: The circling stars

Study this photograph of the Milky Way. Can you see the pointers and southern cross at the top of the arch? Can you identify the Emu in the Sky trailing out to the left from the foot of the Southern Cross in the dark spaces of the Milky Way?
Investigate how constellations change their position in the sky. What factors cause the changing positions?
Describe how the Emu in the Sky changes its position and appearance at different times of the year and the implications for hunting and other activities for different Aboriginal groups. Use the information from the sources on this page to assist you.
Reviewing all the material on this 'Astronomy' page, summarise the similarities and differences between the astronomy that James Cook and the scientists on HMB Endeavour relied on during their voyage and celestial observations, and those of the Aboriginal Peoples discussed in the sources.
While we cannot know what the people of Kamay knew and believed in 1770, we can infer that their knowledge of the stars may have been similar in its approach and meaning to those of other Aboriginal Peoples. Outline your theory as to what the people on HMB Endeavour and the people of Kamay Botany Bay could have learned from one another about astronomy in 1770, if only they had found ways to communicate.

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