To use a star chart to identify stars and constellations, you must first find the one appropriate for the time of year you are observing. Picking the chart appropriate for the season is important because as the Earth orbits the Sun, the Sun’s glare hides many of the stars.
Acquiring The Right Chart
You should be able to be exposed to four charts, one for each season of the year. (These seasons are labeled for the northern hemisphere). Thus, if you want to learn the winter constellations, pick the winter chart.
Because each night the stars move across the sky, rising in the east and setting in the west, you also need to consider the time of night. Once you have found the appropriate chart, you need to match it to the sky. First, you should match direction. That is, if you are looking south, you need to orient the chart so it shows the southern sky. Let’s say, for the purposes of discussion that you are holding an 8pm star chart.
You will notice that a chart has labels north, south, etc. If you hold the chart so that south is at the bottom, it shows the sky approximately as you would see it looking south, with the center of the chart being approximately overhead. Referring to the chart sketched above, it therefore shows the sky as you would see it looking south at about 8 PM in December. (Some charts use sketches only, and most of the stars are omitted.)
With the correct chart in hand you are now ready to match it to the night sky. Two steps are helpful here. First, look for star patterns. Second notice the relative brightness of stars in the pattern. The chart shows the relative brightness of the stars by their size. Dim stars are shown as tiny dots. Bright stars are shown by big dots. With that in mind, do an exercise and try to identify Orion.