## A Taste of Real Astronomy — The ESA/ESO Astronomy Exercises

Six booklets

The exercises are now available on the web and in six booklets (100 pages in total), titled:

"General Introduction" (an overview of the exercise series),
"Toolkits" (explanation of basic astronomical and mathematical techniques),
"Exercise 1: Measuring the Distance to Supernova 1987A",
"Exercise 2: The Distance to Messier 100 as Determined by Cepheid Variable Stars",
"Exercise 3: Measuring the Distance to the Cat's Eye Nebula" and
"Exercise 4: Measuring a Globular Star Cluster's Distance and Age".

The booklets are sent free-of-charge to high-school teachers on request and may be downloaded as PDF files from the web site. More exercises will follow in the future.

Contact: info@astroex.org, www.astroex.org

Exercise 1 - Measuring the Distance to Supernova 1987A

Quick Summary

The geometry of the nearest ring around Supernova 1987A (SN1987A) is introduced. We then define the scale of the Hubble image of the supernova so that the angular diameter of the ring and also the inclination of the ring relative to the plane of the sky can be found. Observations from Earth show how light from the supernova reached the different parts of the ring. Using light intensity measurements and the speed of light, the physical dimensions of the ring can be found. Once both the angular and the physical size of the ring have been determined, we can determine the distance to SN 1987A itself.

Exercise 2 - The Distance to Messier 100 as Determined By Cepheid Variable Stars

In this exercise we measure the period and apparent magnitudes of Cepheid variables in the galaxy M100. The absolute magnitude is derived using the Period-Luminosity relation and the distance to M100 can then be determined using the distance relation. Finally we calculate a value for the Hubble constant (using a value for the recession velocity of M100 observed by other scientists) and estimate the age of the Universe.

Exercise 3 - Measuring the Distance to the Cat's Eye Nebula

Quick Summary

We measure the angular expansion velocity of the Cat's Eye Nebula by careful investigation of two Hubble images taken in 1994 and 1997. With the help of tangential velocity measurements from an earlier scientific paper, it is possible to determine the distance to the nebula. We also derive the distance by looking at how much the radial intensity profiles of prominent features in the two images have changed between 1994 and 1997.

Exercise 4 - Measuring a Globular Star Cluster's Distance and Age

Quick Summary

We measure blue (mB) and green (visual, mV) magnitudes of selected stars in the outer regions of a globular cluster shown on VLT images, convert the (mB-mV) values into stellar surface temperatures (T) and plot the mV values as a function of the T values on a Hertzsprung-Russell diagram. The cluster's Main Sequence, seen in the plotted diagram, is compared with a distance-calibrated standard Main Sequence from the nearby Hyades cluster. The distance to the cluster can be determined by Main Sequence fitting and using the distance modulus. The cluster's age, which incidentally places a lower limit on the age of the Universe, can be estimated from the position of the turn-off point on the Main Sequence.

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