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We use telescopes to
collect lots of light and
focus it onto detectors
using mirrors or lenses.
Large modern telescopes,
like the Keck Telescope
shown below, can collect
6,000,000 times as much
light as the human eye.
Keck Telescope
An open cluster is a group of up to a few thousand stars that were formed from the same cloud of gas and dust, and are still loosely bound (or tied) to each other by gravity.
In contrast, globular clusters are very tightly bound (tied together) by gravity.
Open clusters are found only in spiral galaxies and irregular galaxies, in which star formation is taking place.
The clusters are usually less than a few hundred million years old (very young children in human terms), and are slowly drifting apart.
