 # Natural Science - Year II

#### Course Materials are always under revision! Weblecture content may change anytime prior to two weeks before scheduled chat session for content. History Weblecture for Unit 64

 This Unit's Homework Page History Lecture Science Lecture Lab Parents' Notes

# Natural Science II Lab Exercise for Unit 64: Observing the Colors of Stars

## Goal: to understand how changes in assumptions affect our model of the universe.

### Procedure

1. Read the "Background" link at the lab. Be sure you understand the three variables:
• H0, the Hubble constant or current rate of expansion of the universe. It is determined from the relationship v = H0d, where v is the velocity at which a galaxy appears to be receding (based on Doppler Shift calculations), and d is the distance to the galaxy, based on Cepheid variable or other data. H0 is currently assumed to be about 73 km/s / Mpc (73 kilometers/second for every megaparsec distant the object is: the further the object is, the faster it appears to be moving).
• Ωm is the matter density parameter for the universe. It is a measure of how much mass there is in the volume of the universe.
• ΩΛ is the acceleration parameter. It is a measure of how much dark energy there is in the universe.
2. Begin with the values H0 = 73, Ωm = .24, and ΩΛ = .76. What do the curves for age, size, plot look back look like?
3. What happens if you increase and decrease H0?
4. What happens if you increase and decrease Ωm?
5. What happens if you increase and decrease ΩΛ?

### Report

Create a table with your values for each variable and a description of the resulting curves.

 Hubble ConstantH0 Matter densityΩm AccelerationΩΛ 73 0.24 0.76

For what values are the curves "positive" (up from the lower left to the upper right)? For what values are the curves negative (from the upper left to the lower right)? Can you find three values for which the size curve is "flat" (horizontal)?