As I taught about stars this semester an auditory manner in which to describe absolute and apparent magnitude occurred to me. In this activity volume (of music) will represent the brightness of stars. Absolute and apparent magnitude of the Sun (an average star) and Sirius ( a very bright star) will be compared.
- Star – a large celestial body that is composed of gas and that emits light
- Luminosity – the actual brightness of an object, such as a star
- Absolute magnitude – a measure of how bright a star would be if it were seen from a standard distance
- Apparent magnitude – the brightness of a star, as seen from Earth
- Two devices capable of playing music (iPod, iPad, MP3 player, etc)
- Trundle wheel
- Set one device to the lowest volume possible and the other device to a loud volume (but not so loud that it is uncomfortable to listen to).
- Two staff members should be stationed 86 meters apart. Ideally complete this activity outside so as not to disturb other classes. This distance is measured with the trundle wheel (see materials).
- The staff member closest to the students starting point should be prepared to turn the device on low volume and the other staff member should be prepared to turn the volume of the device to as loud as is comfortable for the students.
- Any music is fine (the Star Wars theme or the Space Odyssey theme would work well). Choose a long-play version.
- Alternatively set the devices up on a stable safe spot if 2 staff members are not available.
Describing the Journey
- Tell students that they are going to travel from our Sun to another star Sirius and consider the relative brightness of the 2 stars.
- We will do this by considering the volume of the music observed as representing the brightness of the star.
- We will travel 8.6 light years to Sirius by utilizing a trundle wheel. Each light year will be represented by 10 meters.
- Have students calculate the number of meters to travel – 8.6 x 10 = 86 meters.
- Starting on Earth – At this point both staff members begin playing music on the devices (very quietly for the Sun and very loudly for Sirius, though students will barely hear it because of the distance.)
- You hear the sound which represents the Sun’s brightness. Notice that from Earth your are barely able to “see” — represented by sound the other star “Sirius.” As observed from Earth (apparent magnitude) which star is brighter? The Earth.
- We will know travel to Sirius to determine the absolute magnitude (how bright it actually is, considered from a standard distance).
- Travel toward the other iPod (or other device) with the students. Choose one student to operate the trundle wheel or taking turns. Have the students count the clicks to 86 meters.
- As the group travels, have students indicate when they can no longer “see”-hear the Sun.
- When you arrive at Sirius – Ask students the following question – You may need to turn down the star first!
- Is the apparent magnitude higher of Sirius? No, because the star is so far from Earth and apparent magnitude is the magnitude as seen from Earth. Remind the students that we could barely hear the sound from the Earth.
- Why? Distance: Absolute magnitude is greater and will be represented by volume.
- How about the absolute magnitude of Sirius? Was it greater or less than the absolute magnitude of the Sun? MUCH greater. Tell the students that in fact Sirius is 70 times brighter than our Sun!
- Return from Sirius to the “whimpy” Sun.
- Review the terms and contrast apparent and absolute magnitude.
- If time allows, have students write a paragraph about the absolute and apparent magnitude of the Sun and of Sirius.
1st Grade – Space Systems, Patterns and Cycles
ESS1.B: Earth and the Solar System
Seasonal patterns of sunrise and sunset can be observed, described, and predicted. (1-ESS1-2)
Middle School – Space Systems
ESS1.A: The Universe and Its Stars
- Patterns of the apparent motion of the sun, the moon, and stars in the sky can be observed, described, predicted, and explained with models. (MS-ESS1-1)
- Earth and its solar system are part of the Milky Way galaxy, which is one of many galaxies in the universe. (MS-ESS1-2)
ESS1.B: Earth and the Solar System
The solar system consists of the sun and a collection of objects, including planets, their moons, and asteroids that are held in orbit around the sun by its gravitational pull on them. (MS-ESS1-2), (MS-ESS1-3)
By Laura Hospitál
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