1. Globular Clusters
By Ryan Hood

2. Definition and Significance
They are Densely packed collections of stars (hundreds of thousands, sometimes millions per cluster)
Used to estimate age of universe.
150 known globular clusters in the Milky May
All stars in a cluster tend to be very similar in age.

3. How do they form? They start as a large accumulation of gas and dust
These gasses and dust start to collect into clumps.
All the stars orbit the clusters center of mass.

4. Metallicity
Metallicity: The abundance of elements in a cluster that are heaver than hydrogen and helium.
Metals (astronomer definition): all elements except hydrogen and helium

5. How do they estimate age?
Globular clusters are chemically homogenous and the stars very close in time to each-other.
We Examine the mass of the of the stars that exceed the main sequence turn off point.
The cluster age is relatively equivalent to the main sequence lifetime of the turnoff stars.
All globular clusters have low metallicity, which follows the characteristics of the early universe, therefore these formed early in the universes existence.

6. Messier 2 Sketch and Photograph
0.34 arcminutes
240X

7. Details of M2 Apparent magnitude: 13.1
Position: Within the Aquarius constellation, roughly light years away from earth.
Diameter: 175 light years
13 billion years old
150,000 stars.

8. How to observe? In some conditions it is visible with the naked eye.
Low power telescopes will show M2 as non-stellar.
Higher power will help distinguish individual stars. (150x or greater)

9. Messier 13 Sketch and Photograph
20 arcminutes 200X

10. Details of M13 Apparent magnitude: 5.8
Position: Within the Hercules constellation, roughly light years away from earth.
Diameter: 145 light years
11.7 billion years old
Contains approximately 300,000 stars

11. How to observe?
Look for the 4 stars that make up the Keystone of Hercules, should be on the western side.
It can be seen with low power visual aid, such as binoculars.
Higher power will show individual stars in the cluster.

13. Messier 22 Sketch and Photograph
32 arcminutes
120X

14. Details of M22 Apparent magnitude: 5.1
Position: Within the Sagittarius constellation, roughly light years away from earth.
Diameter: 100 light years
12 billion years old
Contains approximately 83,000 stars

15. How to observe? Sagittarius constellation
Visible with the naked eye only in very dark skies.
High power telescopes will be best viewing experience

17. Messier 56 Sketch and Photograph
8.8 arcminutes
196x

18. Details of M56 Apparent magnitude: 8.3
Position: Within the Lyra constellation, roughly light years away from earth.
Diameter: 84 light years
13.7 billion years old
Contains approximately 80,000 stars

19. How to observe? Lyra constellation
Not easily visible to naked eye or lower power telescopes, its very dim.
Higher power needed.

21. Sources: https://www.space.com/29717-globular-clusters.html