What is data?
How should we think about data in science?
You probably already have an unarticulated but likely strong sense of what data is: like many other obvious things, you know it when you see it.
One of our tasks will be to define what we mean by data mathematically, but we'll start by exploring a simple example astronomical data analysis.
In optical, X-ray and gamma-ray astronomy, the most basic datasets are images
Images can be 2D, from cameras, or 1D, from spectrographs, or 3D, from IFUs (integral field units).
Image data come packaged as an array of numbers, which we can visualize, and do calculations with.
Let's look at some X-ray image data from the XMM satellite, for the galaxy cluster A1835.