Recovering Hubble's Original Data

Below is what the applet will look like if you select the galaxy N3034 from the Sky Icon. This galaxy has a relatively large diameter and is encompassed by 5 rings. Students are sometimes confused by the images as to what a "galaxy" is. A galaxy will be the largest "black" object that is in the image. In this case, it should be obvious.

The next frame shows the spectrum of N3034 that results when you click on the spectrum tab. The "K" line in this case has an observed wavelength of 3974 angstroms. Students are sometimes confused about where to find the Calcium II H and K lines given the tutorial on the previous page. The key here is that all the galaxies in this data base (the ones that Hubble actually used), are relatively nearby and therefore have very small redshifts. Hence, the Calcium II H and K lines are, at most, shifted by 50 - 105 angstroms from their rest wavelengths. Hence, you should be looking in the area of 3950 to 4100 angstroms to identify this pair of lines. Note also: the yellow text in the green box is wavelength. As you move the green line horizontally along the spectrum you will see this number change.

The case below now shows a relatively small galaxy, N3516. In this case its diameter is less than 1 full ring; probably 0.75 rings.

Clicking on the spectrum tab brings up the spectrum of N3516 where it can be seen that the "K" line has an observed wavelength of 4004 angstroms. Thus, the redshift of N3516 is larger than the redshift of N3034 and the observed diameter of N3516 is smaller than N3034.

Now use the Live Applet below to make measurments of all the galaxies that you can. Measure their angular size and their observed redshift. See if you can find a relation, as Hubble did, between radial velocity and angular diameter and then think about why that relation implies the Universe is expanding. You should measure at least 20 galaxies to help determine this.

Note: Ignore the data tab on the applet as well as the "record measurement" button as these are not fully functional, yet.

Now be Edwin Hubble:

The Graphic below is the applet! Click on it in various places.