# National Aeronautics and Space Administration

## The Hidden Lives of Galaxies - Classroom Activities

### Activity #6b - Evidence for Hidden Mass

In this activity, students will interpret and analyze the information presented on the "Evidence for Hidden Mass" graph. They will observe trends in the graphs, and use it to determine if there is evidence for hidden mass.

The "Evidence for Hidden Mass" graph is on the "Hidden Lives of Galaxies" poster. It is also available as Transparency #6 , as part of the transparency set. The transparencies are available at
http://imagine.gsfc.nasa.gov/educators/galaxies/transparencies/.

Worksheet Answers

1. There are 9 Solar System planets presented on the graph. The planets from the closest to Sun to the furthest from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

Using the graph, the velocities of the solar system planets, from the lowest value to the highest value, are approximately 48, 35, 30, 24, 13, 10, 7, 5, 4 km s-1.

Using the graph, the distances of the planets from the Sun are, from least to greatest, 0, 110, 150, 250, 800, 1500, 2800, 4500, 6000 million km.

In general, the further the planet is away from the Sun the slower the velocity. The closer the planet is to the Sun the faster the velocity.

2. Answers should include the distance ranges from 0 to about 19 kpc, and the velocity ranges from 0 to 100 km/s. The velocities first increase with increasing distance. But at distances larger than 10 kpc, the velocity becomes constant with increasing distance.

 A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Andy Ptak (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC