PHYSICS 20B Lecture Notes - Lecture 12: Hockey Puck, Saga Of Cuckoo, Red Dwarf
Lecture 12
Discovering the Milky Way (1)
● The Milky Way (backstory)
○ There are 6000 stars visible by the naked eye in the sky, and the farthest star
being approx. 4000 light years away
○ There is a total of 2000 Billion stars in the Milky Way
○ The diameter of the Milky Way is about 100,000 light years
■ Our Sun is approx 26,0000 light years away from the center of the Milky
Way
■ The Sun is orbiting around the center of the Milky Way at approx 200
km/s.
● One orbit every approx. 200 Myrs.
○ Most stars in the Milky Way are red dwarf stars,
■ Only less than 10% are stars similar to our sun
■ A tiny fraction of ~1% are massive, blue stars.
● Solar Neighborhood
○ In our solar neighborhood, stars are usually approx 6 light years apart from each
other,
○ The Sun’s age is typical to that of similar stars, being approx. 4.5. Billion years
● Central bulge/bar:
○ In the central area of the Milky Way, stars are usually around ½ light years apart
○ Stars in this area are also older than the our Sun, the stars being at least 10
billion years old
● Charles Messier (initiator)
○ Compiled a list around 100 different fuzzy objects
○ He did this in order to help identify which ones are comets
○ Became well known for his beautiful collection
● William Herschel
○ Tried to map the Milky Way through the observations of stars
■ He thought that if he saw a direction with less stars, that was the towards
the edge of the galaxy, and if he saw many stars, then the edge was very
far away
■ He concluded the the Milky Way looks similar to that of a giant hockey
puck
● Kapteyn
○ Updated Herschel’s map by observing more stars
○ Kapteyn concluded that the Sun was near the center of the Milky Way
■ However, because our vision of sight in our own universe is limited, we
can not merely see the entirety of the galaxy, just a small space in our
universe,
● Also there is gas and dust present that prevents us from seeing
further into the galaxy around us
● Light gets absorbed by gas and dust
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
There are 6000 stars visible by the naked eye in the sky, and the farthest star being approx. There is a total of 2000 billion stars in the milky way. The diameter of the milky way is about 100,000 light years. Our sun is approx 26,0000 light years away from the center of the milky. The sun is orbiting around the center of the milky way at approx 200 km/s. Most stars in the milky way are red dwarf stars, Only less than 10% are stars similar to our sun. A tiny fraction of ~1% are massive, blue stars. In our solar neighborhood, stars are usually approx 6 light years apart from each other, The sun"s age is typical to that of similar stars, being approx. In the central area of the milky way, stars are usually around light years apart. Stars in this area are also older than the our sun, the stars being at least 10.
