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The Corona Borealis is a small constellation located near Bootes' head. The "jewel" of the crown is a 2.4 magnitude star called Gemma.
You might be wondering why should the stars go around the North Star once every 23 hours 56 minutes and 4 seconds. This is because the earth rotates on the average every year 366 1/4 times. Doesn't the year have 365 1/4 days (the quarter day is taken care of by leap year)? Where does the extra revolution come from? Yes, the Earth does rotate around its axis 365 1/4 days a year, but it also rotates around the Sun once a year. A star's daily motion is determined both by the Earth rotation around its own axis (365 1/4) and the Earth's revolution around the Sun (1). If you divide up a full year by 366 1/4 you get 23 hours, 56 minutes and 4 seconds, a period called a sidereal day. Every 23hr,56min,4sec a star will appear in the exact same position in the sky. Since our days are 24 hours, if you look at the sky at the exact same standard time at night, from night to night, the star's position will change. This is why Orion can be seen high overhead during the winter, while a constellation such as Scorpio is best seen during the Summer.
Last week we discussed declination - the celestial equivalent of latitude. The celestial equivalent of longitude is called right ascension. Right ascensions are imaginary lines that run from one celestial pole to another. Traditionally a right ascension is measured in hours, minutes and seconds and its value can vary from 0 to 24 hours.
So every star is at an intersection of two lines: declination and right ascension. If you take a look at the constellation diagram on this web page or better yet go on to the next page Hercules you will the lines of declination and right ascension. Lines of declination have a small degree sign after their number while the lines of right ascension are labeled with a small "h".
Right ascension and declination are very useful for finding something on a sky map and are used to indicate a location of a new comet. Any object in the sky can be pinpointed with right ascension and declination that change very slowly for the stars, more rapidly for the planets and much more rapidly for the Moon. It is not a simply matter to directly use right ascension and declination to find an object in the sky because the Earth's rotation causes the stars to move through the sky, but knowing them will help you find the object on a sky map which can then be used find the object in the sky.
Hercules