Last week we covered multiple star systems, but what if we added thousands or even millions of stars to the mix? A star cluster. There are different kinds of clusters, though. Open clusters contain hundreds or thousands of stars held together by gravity. They’re young, and evaporate over time, their stars let loose to roam space freely. Globular clusters, on the other hand, are larger, have hundreds of thousands of stars, and are more spherical. They’re very old, a significant fraction of the age of the Universe itself, and that means their stars have less heavy elements in them, are redder, and probably don’t have planets (though we’re not really sure).

Crash Course Astronomy Poster: store.dftba.com/products/crashcourse-astronomy-poster

--

Table of Contents
Open clusters contain hundreds or thousands of young stars 00:29
Over time, open clusters evaporate 3:23
Globular clusters contain hundreds of thousands of old stars in spherical formation 5:50
Globular clusters have less heavy elements, thus probably do not have planets 6:43

--

PBS Digital Studios: youtube.com/pbsdigitalstudios

Follow Phil on Twitter: twitter.com/badastronomer

Want to find Crash Course elsewhere on the internet?
Facebook - www.facebook.com/YouTubeCrashCourse
Twitter - www.twitter.com/TheCrashCourse
Tumblr - thecrashcourse.tumblr.com
Support CrashCourse on Patreon: www.patreon.com/crashcourse

--

PHOTOS/VIDEOS
Magellanic gemstone in the southern sky [NGC 290] www.spacetelescope.org/images/heic0603c/ [credit: European Space Agency & NASA]
Extreme star cluster bursts into life in new Hubble image www.spacetelescope.org/images/heic0715a/ [credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration]
View of a Sun-like star within an open cluster (artist’s impression) www.spacetelescope.org/videos/heic1321d/ [credit: NASA, ESA, and M. Kornmesser]
Motion of stars in Omega Centauri www.spacetelescope.org/videos/heic1017a/ [credit: NASA, ESA, J. Anderson and R. van der Marel (STScI)]
47 Tucanae: Probing Extreme Matter Through Observations of Neutron Stars chandra.harvard.edu/photo/2013/47tuc/ [credit: NASA/CXC/Michigan State/A.Steiner et al]
Hubble Refines Distance to Pleiades Star Cluster hubblesite.org/newscenter/archive/releases/2004/20/image/a/ [credit: NASA, ESA and AURA/Caltech]
M45 Pleiades www.noao.edu/image_gallery/html/im1116.html [credit: T.A. Rector (University of Alaska Anchorage), Richard Cool (University of Arizona) and WIYN]
From the Pleiades to the Hyades www.deepskycolors.com/archive/2011/11/06/from-the-Pleiades-to-the-Hyades.html [credit: Rogelio Bernal Andreo]
Messier 035 Atlas Image commons.wikimedia.org/wiki/File:Messier_035_2MASS.jpg [credit: Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation]
Globular cluster 47 Tucanae www.spacetelescope.org/images/heic1510a/ [credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration]
The oldest cluster in its cloud www.spacetelescope.org/images/potw1428a/ [credit: ESA/Hubble & NASA]
An unexpected population of young-looking stars www.spacetelescope.org/images/potw1244a/ [credit: ESA/Hubble & NASA]
View of a globular cluster (artist’s impression) www.spacetelescope.org/videos/heic1321c/ [credit: NASA, ESA, and M. Kornmesser]
All that glitters www.spacetelescope.org/images/potw1449a/ [credit: ESA/Hubble & NASA]

1. Introduction to Astronomy
2. Naked Eye Observations
3. Cycles in the Sky
4. Moon Phases
5. Eclipses
6. Telescopes
7. The Gravity of the Situation
8. Tides
9. Introduction to the Solar System
10. The Sun
11. The Earth
12. The Moon
13. Mercury
14. Venus
15. Mars
16. Jupiter
17. Jupiter's Moons
18. Saturn
19. Uranus & Neptune
20. Asteroids
21. Comets
22. The Oort Cloud
23. Meteors
24. Light
25. Distances
26. Stars
27. Exoplanets
28. Brown Dwarfs
29. Low Mass Stars
30. White Dwarfs & Planetary Nebulae
31. High Mass Stars
32. Neutron Stars
33. Black Holes
34. Binary and Multiple Stars
35. Star Clusters
36. Nebulae
37. The Milky Way
38. Galaxies, part 1
39. Galaxies, part 2
40. Gamma-Ray Bursts
41. Dark Matter
42. The Big Bang, Cosmology part 1
43. Dark Energy, Cosmology part 2
44. A Brief History of the Universe
45. Deep Time
46. Everything, The Universe...And Life
47. Explore The Solar System:

In this Crash Course series, marvel at the wonders of astronomy with your host for this intergalactic adventure, the Bad Astronomer himself -- Phil Plait. In just 40 short lessons, you will learn the basics of the oldest science known to humanity.

Be sure to check out links to relevant Photos in the description for each video.