Messier 3 – Globular Cluster
The third in turn object of the Messier catalog is Messier 3, which is a Globular Cluster. It was the first object to be discovered by Charles Messier himself. The globular cluster is located in the constellation of Canes Venatici. The cluster is roughly 34,000 light years from earth and contains over 500,000 stars. Being located near the Hercules Globular Cluster (Messier 13), it makes it one of the most popular targets for amateur astronomers.
One thing that distinguishes this Globular Cluster from the rest, is that it contains more variable stars than any other known cluster. Astronomers can use variable stars in order to use those stars' brightness fluctuations and estimate their distances. This also helps measure distances of deep-sky objects.
Facts
Type: Globular cluster
Magnitude: 6.2
Right Ascension : 13h 42m 11.62s
Declination: +28° 22′ 38.2″
Distance: 34,000 light years
Constellation: Canes Venatici
Best viewed during: Spring - Summer
Observation
Locating Messier 3 Globular Cluster is fairly easy, as it lies in the southern part of the constellation Canes Venatici and on the border of the constellation of Bootes.
Both Canes Venatici and Bootes constellations are best visible during spring.
Messier 3 can be located 12 degrees northwest of the orange giant star Arcturus and about halfway along an imaginary line between Arcturus and Cor Caroli.
How to locate it
First you have to locate the orange super giant star Arcturus which is located in the constellation of Bootes. It is the fourth brightest star in the night sky, so during spring it is fairly easy to locate.
The hand and finger method can also be used to navigate your self to Messier 3. The tip-to-tip span between your index finger and your little finger is 15°. And since the globular cluster is located roughly 12 degrees northwest, you can locate it fairly easy.