MGMT 1050 Lecture Notes - Lecture 10: Harlow Shapley, Virgo Supercluster, Gravitational Lens

10 views17 pages
20 Jul 2016
Department
Course
Professor
CH 10: Discoveries about Galaxies and the Universe
Part One: Early Theories about "Nebulae"
1. The Ancient Greeks reported nebulae in the sky (Latin: “clouds”) (2500 Years ago)
1. Two of the brightest naked eye Nebulae are in the southern hemisphere sky
2. Ancient sky watchers from the middle east referred to these nebulae as the Arabic for
sheep
3. Today the two brightest Nebulae are called the Large Magellanic cloud and the small
Magellanic cloud after Portuguese explorer Ferdinand Magellan
1. In the 1750s, the telescope revealed: some nebulae are elliptical
1. It was proposed: elliptical nebulae are disk-shaped star systems (“Island Universes”),
and that we live in one such system. This theory was proposed by Emmanuel Kant
Meaning that each elliptical nebula can be composed of billions of stars that have
grouped together into a flattened circular system of stars/a disk.
If these disk system are randomly oriented throughout the universe then we are seeing
them at all different angles. That’s going to cause them to appear as ellipses.
An ellipse is a circular disk viewed at an angle.
Became know as the Island Universe theory: the stars we see around us make up a star
system that is just one out of numerous star systems out there
The bright band of light seen across the night sky was named “galaxy” by the Ancient
Greeks (Greek: milky). Today we call it the Milky Way.
Why does one strip of sky have so many more stars than the rest of the sky?
Kant correctly explained: if we live in a disk-shaped star system then the milky way is
simply our view through the disk’s length.
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 17 pages and 3 million more documents.

Already have an account? Log in
1. 1770s-1840s: William Herschel and son John used their giant telescopes to catalogue
over 5000 nebulae.
William Herschel excellent telescope maker. Discovered Uranus. Was interested in
cosmology. Had the biggest and best quality telescopes around.
Prior to Hershel, Charles Messier had the biggest catalogue for nebulae (~110 objects)
Herschel saw Messier’s 110 Nebulae and looked for more. He went from 110 to 2500
Nebulae.
John found a couple thousand more Nebulae after his father became sick. He then
published a Nebulae catalogue (had over 5000 nebulae in it)
They (Herschel) attempted to identify whether nebulae are distant star systems or
nearby glowing gas clouds.
Herschel couldn’t answer this question (wondered if all nebulae were different shapes &
sizes or just glowing gas clouds)
Orion Nebula is the brightest and biggest nebulae in the sky
Owing to the large variety of nebulae, the Herschel’s couldn’t come to a general
conclusion about their composition
M9 was a Nebulae which Herschel observed and said it contained clusters of stars.
M17 couldn’t resolve this Nebulae into stars. It doesn’t contain any stars but Herschel
tried to fit this Nebulae in his theory. He said it could be really distant and contain stars.
M33 Herschel said he could see the stars in the middle. But the cloudy parts remained
cloudy even if he zoomed in.
He couldn’t conclude that all nebulae were distant star systems.
Part Two
Herschel produced a rough map of our star system by assuming that the brightest stars
are nearest and the faintest stars are furthest. Despite the many exceptions to this, his map
revealed our disk-shaped system.
The picture on the bottom part was taken from the earth. It shows an edge on view of
our galaxy.
Light from the center of our galaxy can’t be seen because of how dirty our galaxy is. So
the picture had to be taken in Infrared light.
Herschel’s map revealed that Kant was correct in his proposal that the shape of our star
system is flattened/disk like.
Hershel attempted to produce a map of all visible stars around the sun as we would see
it from outside our solar system
oWould show how stars distributed
oNeeded to know distance to all visible stars
oOnly option judge distance from its brightness
oDid however, manage to correctly convey a flattened (disk-shaped) star system
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 17 pages and 3 million more documents.

Already have an account? Log in
1845: Rosse, with his leviathan telescope, attempted to prove that all nebulae are star
systems by resolving their stars.
Built the largest telescope of his time after Herschel. His telescope remained the largest
reflecting telescope in the world for 70 years.
Hoped to solve mystery of nebulae
While Rosse’s evidence of stars was not definitive, his detailed sketches revealed: many
elliptical nebulae are “spiral nebulae”.
Looking at Orion Nebula, linked some of the bright stars to the nebula itself (today
know they aren't connected, are in the foreground)
oConcluded that all nebulae are in fact star systems (no such thing as gas clouds)
oSimply appear cloudy because they are so packed with stars
When he looked at the elliptical nebulae, noticed that many were "spiral" (became
known as spiral nebulae)
Galactic cannibalism can be observed in the sketch below. The galaxy to the right of this
big galaxy is slowly being consumed by the one in the middle.
Henrietta Leavitt (1868-1921)
While cataloguing stars in photos of the Magellanic clouds (our two nearest galaxies),
she discovered thousands of variable stars (star which fluctuate in brightness at regular time
intervals).
The type of stars she was dealing with are called Cepheids
Cepheids: luminous variable stars which pulsate rapidly (at intervals of days to weeks).
They are luminous, high mass stars (10 to 20 times more than the sun) that pulsate
dramtically and rapidly
oOver a few nights, can change its apparent brightness by one to two magnitudes
First variable star to be discovered is known as Delta
The reason these stars brighten and fade is because they’re physically pulsating. They
grow in size and then shrink
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 17 pages and 3 million more documents.

Already have an account? Log in

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class
Class+
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
1 Booster Class