Astronomical scale

​This focus idea is explored through:

Contrasting student and scientific views

Student everyday experiences

A student is looking through a telescope at the daytime sky.Students interpret reality from their perspective of the world around them. As a result their everyday thinking about space and time is often limited to local conditions; often at most perhaps hundreds of kilometres or decades of years. Vast distances and times are central ideas in ‘the changing Earth and its place in space’. However these ideas are very difficult for students to grasp. This has very important implications for their learning of ideas about distances in space or very long spans of time. It is, for example, difficult for most students to conceive that a deep valley could have been carved out over many millions of years by the small river at the bottom. Similarly the universe is so large that it is almost impossible to imagine and we even use a new unit of distance to describe the vast distances in the universe. This unit is the light year. Students often find it confusing to express a distance with the term ‘year’ as we usually use this term to describe a period of time. This unit of distance is poorly understood by most adults.

Scientific view

A light year is the distance that light travels in one year. The light from the sun takes about eight minutes to reach the Earth because it is only a relatively short astronomical distance (about 149 million km) away. The light from distant astronomical objects takes so long to get to us that we see these objects as they appeared a long time ago.

Our solar system is one of many that make up our galaxy, the Milky Way. Our galaxy has a diameter of close to 100,000 light years and contains between 200 – 400 billion st​ars which vary in size and brightness and are distributed throughout the galaxy. Our galaxy is one of probably more than one hundred billion galaxies that make up the universe. Some distant galaxies are so far away that their light takes several billion years to reach Earth.

The sun is many thousands of times closer to the Earth than any other star. Hence it looks brighter and bigger than any other star. Light from the Earth’s nearest star other than the sun (Alpha Centauri, one of the pointers near the Southern Cross) takes just over 4 years to travel to Earth. The trip to that star would take the fastest rocket we can currently build thousands of years.

Our solar system originated from a giant cloud of gas and debris left from the explosion of stars five billion years ago. Everything in the universe and on Earth is made of this material. Scientific evidence implies that some rock near the Earth’s surface is several billion years old.

The Earth’s surface is shaped by water (including ice) and wind over very long times. The change is so slow that it is hard to observe rock erosion and soil formation. Biological evolution is also difficult to observe due to the very slow changes that occur.

Critical teaching ideas

  • Space is so large that we use a completely different unit to represent distance; the light year which is the distance that light travels in one year. (This is 65,700 times the distance from the Earth to the sun.)
  • The universe is so large that it is almost impossible to imagine.
  • It has been such a long time since the universe and even the Earth first came into being that our lifetime is insignificant.
  • Some changes are so slow they are very hard to see in one lifetime. Some examples are evolution, soil formation and rock erosion.

Explore the relationships between ideas about astronomical scale in the Concept Development Maps – Stars

Students are often fascinated with statistics which describe space and time. Through discussion their ideas can be explored. In order to understand the ideas students need to explore visual scale models and timelines. Their understanding is further enhanced if they create these themselves.

Teaching activities

Practise using and build the perceived usefulness of a scientific model or idea

Students could construct a time line to gain perspective of the vastness of time and our lifetime in reference to it. Examples of timelines are ‘the origins of the solar system’ and ‘life on Earth’. If a helpful scale is used a time line representing the age of the Earth can be displayed around the walls of their classroom.

Students could construct a scale model of the solar system with both distances and size of planets to scale. If an orange is used to represent the size of the sun then the model of the solar system should fit into the size of an average school oval.

The closest star to Earth other than the sun is Alpha Centauri. Students can build a scale model which includes the distance between the Earth and the sun and the Earth and Alpha Centauri.

Several ideas for the development of a scale model of the solar system which will fit in most school grounds are available at the Lunar and Planetary Institute:

Clarify and consolidate ideas

Students can use an online calculator to construct scale models at the Science Exploratorium:

Students can explore a variety of sites useful for the investigation of astronomical distance. A good selection is available at the Vendian site:

Promote reflection on and clarification of existing ideas

To build a sense of how large astronomical distances are first ask students to consider how long it would take to drive a car to the moon. This time will be one the students can imagine. Now compare this with how long it would take to drive to the sun. This is a figure that is still imaginable but is now outside the students’ lifetime. Extending this by driving to the nearest star/edge of the galaxy/another galaxy will highlight the point that the distances become unimaginable.

Students can investigate how long it will take to visit astronomical objects using speeds of their choice at the University of Maryland site:

A similar activity could be performed for time by using timelines (similar to geological time).

Further resources

Science related interactive learning objects can be found on the FUSE Teacher Resources page.

To access the interactive learning object below, teachers must login to FUSE and search by Learning Resource ID:

  • The wonders of our universe: space traveller - students can explore our place in the universe from a spaceship. They can see where planet Earth and the solar system fit within a spiral galaxy containing millions of stars.
    Learning Resource ID: Y9CY8C