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Apparent Magnitude Teacher Sheet

Apparent Magnitude Teacher Sheet Photo Credit: Clipart.com

Introduction

You have introduced your students to apparent magnitude, luminosity, and distance of stars. Now you will introduce them to the GoSkyWatch Planetarium app, which can help students figure out those things about stars.


Now introduce students to the GoSkyWatch Planetarium app on the iPad or iPhone. Explain to the students that the app visualizes the night sky, looking into space from the Earth without anything blocking one’s vision, such as clouds, buildings, other lights, or smog. The app shows stars from any place on Earth, including what the sky looks like on the opposite side of the planet—as if you could look straight through the Earth and into space. Point out to students that there is a red icon at each of the four corners of the app. The heart icon at the bottom left is for sharing via social media, which should be turned off on classroom devices. The clock icon on the bottom right refers to the date and time; this setting should already be set.

The magnifying lens icon on the top left opens to reveal five additional icons in red circles. The planet icon allows students to find and learn more about the sun, moon, and planets in our solar system. When any one is selected, the app will locate it using four blinking pointers. The Cassiopeia icon allows students to learn more about and identify the visible constellations. The galaxy icon allows students to search for Deep Sky Objects, such as nebulas, clusters, and galaxies. The list can be ordered by name, distance from Earth (closest to farthest), or magnitude (brightness). The star icon allows students to search for any visible star by name, distance from Earth, or magnitude. Finally, students will notice a birthday cake slice icon, which allows them to set their birth date. The stars are then organized by how old they were when the light that they currently see was emitted from the star. This is a fun feature that really shows students that it literally takes time for light to travel and that the light they are seeing now from stars in the night sky was emitted some time ago. All of the icons allow students to sort the astronomical objects by "All" or "Visible." 

The gears icon on the right opens up to three icons and one vertical bar. The vertical-line bar allows students to set the brightness of the night sky, making more or fewer stars visible. It is a helpful tool to show what the night sky would look like without any pollution or barriers. The wrench icon allows students to turn display effects off or on. For example, visualization of the Milky Way can be turned off or on, depending on what is actually visible in the night sky for students. If students are looking at the sky at night with the app, the Night Mode feature will switch to red lighting, preserving their night vision. Finally, the location icon should already be set and the question mark icon links to the online user guide.

Provide students some time to explore the night sky using the app. Ask them to use the icons to find the Little Dipper. This is listed as Ursa Minor (Little Bear). Have the students tap the “GoTo” button on the top right of the content box.

Ask students to refer back to the image of the Little Dipper that was provided to them at the beginning of the lesson. Using the app, students should record the apparent magnitude and distance of each of the seven major stars on the handout. This can be done by moving the small circular icon in the display over each of the stars. The apparent magnitude is indicated by a star symbol under the name of the star. Once everyone has completed the work, generate a classroom table with this information, provided by the students:

Name of Star in Little Dipper

Apparent Magnitude

Distance

Polaris

2.0

430 ly

Yildun

4.3

180 ly

Epsilon Ursae Minoris

4.2

350 ly

Zeta Ursae Minoris

4.3

380 ly

Eta Ursae Minoris

4.9

97 ly

Pherkad

3.0

480 ly

Kokhab

2.1

130 ly

 

Ask students:

  • Of the seven stars, which one is the brightest? 
    • (Polaris is the brightest.)
  • How do we know? 
    • (It has the lowest apparent magnitude.)
  • Which star is actually the closest to us? 
    • (Eta Ursa Minoris is closest at 97 light-years away.)
  • Which star is the furthest? 
    • (Polaris is the furthest.)

Students should turn off the images for the constellations in the settings by going to the wrench icon. This will allow them to see the relative sizes of the stars more clearly. Ask students to identify which two stars are the biggest and brightest. These are Polaris and Kokhab, which also correspond to the lowest apparent magnitudes.

Remind students that the scale of apparent magnitude was originally proposed in 150 B.C.E., more than 2000 years ago by a Greek mathematician, Hipparchus. This original scale went from 1 through 6, where a first magnitude star was the brightest object he could see, a second magnitude was the second brightest, and the sixth was the least visible or faintest object he could see. However, over time, this scale has been modified and extended. 

Ask the students to find the brightest star in the sky using the app. Allow the students to come up with different ways to identify this star. They may, for example, go through the night sky and identify the brightest stars by choosing what seem like the biggest and brightest to them. Some students may go to the star icon in the upper left and sort by magnitude. In any case, students will find that Sirius is the brightest star in the sky with a magnitude of -1.4, visible in the winter months in the Northern Hemisphere. Students can continue to identify the magnitudes of different astronomical objects and these can be compiled into a class chart. For a good example, see The Magnitude Scale

Now students should go to the star icon in the upper left and find where Polaris stands with reference to being the brightest star in the sky. They will notice that Polaris, at a magnitude of 2.0, is far from being the brightest star, which is a common misconception. Ask students to find a star with an apparent magnitude of 0; this is Vega. 

This teacher sheet is a part of the Star Light, Star Bright lesson.

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