The observable Universe
The way humans have observed the Universe has developed throughout history. At first the only information available was what could be observed by eye. The invention of the telescope meant that much more detailed observations could be made, and it became possible to see objects much further away.
Modern increases in the size and sensitivity of telescopes have meant that observations can be made to incredible distances and the very faintest of stars.
Invisible observations
Modern technology can be made sensitive to electromagnetic frequencies that human eyes cannot sense. This has opened up areas of astronomy that were not available previously. Observing the radio waves or infrared or X-ray emissions from stars and galaxies has allowed scientists to make a huge number of discoveries in a very short time.
Space telescopes
Many of the extra wavelengths of EM waves that astronomers would like to observe do not penetrate the atmosphere. This means that any telescope which is to use these parts of the EM spectrum, such as most ultraviolet light, needs to be based on a satellite above the atmosphere. The Hubble Space Telescope has detectors for visible light and also for infrared and ultraviolet.
Putting telescopes on satellites also has the advantages that they are not affected by the weather, or by day and night light levels.