Astronomy Principles and Practice Fourth Edition.pdf

Simple observations 37
Figure 6.4. The major features of Orion and Taurus.
Figure 6.5. The bright stars of Leo.
Close inspection of the pattern reveals that it is actually made up of eight stars, as there are two Mizar
and Alcor (ζ and 80 UMa) separated by 11 minutes of arc. The separation of the stars Dubhe and
Mirak (α and β UMa) is about 5 ◦ : the distance between Polaris (α UMi) and Dubhe (α UMa) is close
to 30 ◦ . It may be noted that the northern hemisphere sky appears to rotate or pivot about a point very
close to Polaris. There is no equivalent ‘pole star’ in the southern hemisphere. The sides of the Square
of Pegasus (see figure 6.3) are approximately 16 ◦ across the sky.
Over the course of a few weeks, take note of the changes in rising and setting times of the
constellations. This can be done by noting the times when a particular group of stars is at the same
position in the sky relative to a particular position of a land-mark as seen from some regular observing
point. Better still, fairly accurate transit time records can be made over a few nights by using a couple
of vertical poles fixed in the ground a few metres apart.
For northern hemisphere observers, it may be noted that the star cluster known as the Pleiades
(see figure 6.4) may be seen rising in the east in the autumn. As winter progresses the rising time