The idea of long-slit spectroscopy is to only observe the spectrum of an object along a narrow line. From this we can determine the motion of stars in the galaxy.
Depth of Field
A 3D map of the Pillars of Creation has been made, and from it we know they will still be around for millions of years.
Light Me Up
One of the properties of atoms and molecules is that they interact with light in an interesting way. If you heat up atoms or molecules in a gas, they will give off light. But they only give off light at specific wavelengths (colors).
Rainbow Star
Spectroscopy is one of the most useful tools of modern astronomy. With it we can identify the atomic and molecular composition of celestial objects, we can measure the relative motions of stars, and we can observe the expansion of the cosmos. Modern telescopic spectroscopes generally use a device known as a diffraction grating.