A finder chart (such as Figure 1 for the open cluster, NGC957) allows an astronomer to identify particular stars within an image. For example, in creating a colour magnitude diagram, it is important that the measurements taken in the two filters (normally B and V) correspond for each star, allowing an easy calculation to be made of the star's colour index. It also allows an easy comparison to be made between astronomers who can simply quote a unique number for each star, rather than describing its position of using its RA and dec co-ordinates. The easiest way of collecting data for a set of stars is to perform photometry in the order in which the stars are numbered - this is particularly useful when creating a CMD since it is the comparitive brightness of stars in multiple filters (in this case B and V) that we are interested in.
The easiest ways of creating a finder are:
- Print off the image and write the numbers on
- Convert the image (you can use 'Save As' within Makali'i) to a jpeg and use a program such as Paint to add the numbers in
- Use a FITS viewer such as DS9 to add the numbers in and then save as a jpeg
Download the sample dataset for the open cluster NGC957.
Explore further datasets.
Plot your data.