Through the telescope a real star cluster shone – dozens of stars in golden, blue and reddish colours, close together. Liri tried to count them, and stopped short. “That is how I used to watch the sky above my home, too! But all I remember is: there were far more blue stars than reddish ones…”
In a tally chart you make one mark for every thing you count. The fifth mark is drawn across the other four – that makes it easier to read.
The tally chart becomes a frequency table – the marks as clear numbers:
| Star colour | Number |
|---|---|
| Golden | 7 |
| Blue | 10 |
| Reddish | 3 |
Enter your own values – the bar chart appears live:
Astronomers use charts to sort thousands of stars by brightness and temperature – the famous Hertzsprung–Russell diagram shows at a glance how stars change over the course of their lives.
Space telescopes such as Hubble also collect huge amounts of data that only become understandable through tables and charts.
In tally charts people often forget to draw the fifth mark across the others! Without the bundles of five, counting up at the end becomes much slower and more error-prone.
Liri looked at her finished bar chart – at a glance she could see which star colour appeared most often in the sky. She wrote the pattern onto her star map.
Liri can now collect data, sort it and show it in charts.