The above technical definition works well, but for ordinary sky watching, it is helpful to start with a simpler scheme using just your hand at arms length. The figure shows that this distance is about 20 degrees. The figure below shows how that angle can be found for the size of the "bowl" in the star grouping we call the Big Dipper. If you hold these sticks up to your eye and sight along one to a given star and along the other to another star and then measure with a protractor the angle between the sticks, you will have found the angular distance between the two stars. To understand how, imagine two sticks joined at one end with a nut and bolt so they can be spread apart. Technically, we measure size on the sky by angular measure.Īstronomers traditionally use angles to measure sizes and distances on the sky. That is, how much of the sky does it span. When we talk about the size of a constellation, we are referring to how big it looks to us. Sky does Orion cover? For example, could you cover it with your thumb at arms length? For example, Orion is much larger than Cassiopeia. You can also see that they differ in size. You have seen that Orion, Taurus, and Cassiopeia each have a different shapes (H, V, and W). Taurus the Bull is easy to find if you think of his bright red eye (the star Aldebaran) and his horns that form a "V." Orion thus has a roughly "H" shape.įind Taurus on the Winter chart. He is usually depicted as a standing figure with raised arms, one arm holding his shield, the other his club to defend himself against the bull, Taurus. The sketch below shows the outline of the constellation Cassiopeia.įind Orion the Hunter. roughly a "W." (You can remember this if you think of the "W" as the chair or throne on which Cassiopeia, the Queen, sits). Find Cassiopeia on the Winter Chart and notice its shape. To learn the constellations you need to learn not only their shapes but also their relative sizes. What direction should you look to see the constellation Orion? Whatĭirection should you look to see the constellation Cassiopeia? Use the sketch of the chart to find the constellations Orion and Taurus on Notice that the chart shows that Orion has two bright stars on either side of a dimmer line of three stars, which form Orion's belt. Relative brightness of the stars by their size. The relative brightness of stars in the pattern. With the correct chart in hand you are now ready to match it to the night sky. (Keep in mind that this is only a sketch. Therefore shows the sky as you would see it looking south at about 8 PM in December. Referring to the chart sketched above, it Is at the bottom, it shows the sky approximately as you would see it looking south, with theĬenter of the chart being approximately overhead. You will notice that the chart has labels north, south, etc. That is, if you are looking south, you need to orient the chart so it shows the southern sky. Once you have found the appropriate chart, you need to match it to the sky. The charts we will discuss below show the sky as it appears about 8 PM local time. In the west, you also need to consider the time of night. You want to learn the winter constellations, pick the winter chart, which is sketched in very rough outline above.īecause each night the stars move across the sky, rising in the east and setting (These seasons are labeled for the northern hemisphere). In the back of the text book and on the inside front cover, you will find four charts, one forĮach season of the year. The chart above is labeled "Winter." 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. To use a star chart to identify stars and constellations, you must firstįind the one appropriate for the time of year you are observing. A typical star chart (see below) shows the relative positions of the stars and their brightness. With it, you can identify and locate constellations and stars.
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