(Discussion – Galaxies; Video – HTUW Alien Galaxy Part 1) Thursday September 21, 2017 (Discussion – Galaxies; Video – HTUW Alien Galaxy Part 1)

The Launch Pad Thursday, 9/21/17 Describe what the following pictures illustrate: A planetary nebula with white dwarf

Describe what the following pictures illustrate: The Launch Pad Thursday, 9/21/17 Describe what the following pictures illustrate: A supernova remnant

Describe what the following pictures illustrate: The Launch Pad Thursday, 9/21/17 Describe what the following pictures illustrate: a nebula

Announcements We will take Quiz 3 tomorrow! Remediation for Quiz 2 runs through tomorrow at 5:00. We will take Quiz 3 tomorrow!

F8 S2 F9 QUIZ 2 9/14 9/15 5:00 PM 9/19 Overdue Last Day Accepted Assignment Currently Open Summative or Formative # Date Issued Gone Missing Day Last Day Accepted DE – Stars F8 9/14 Overdue QUIZ 2 S2 9/15 Tomorrow 5:00 PM eResearch Paper – Star Stages F9 9/19 Next Wednesday

Galaxies Our Own Milky Way Galaxy The Milky Way’s structure was determined by using radio telescopes. It is a large spiral galaxy about 100,000 light-years across. It’s thickness at the galactic nucleus is about 10,000 light-years. The Milky Way has three spiral arms of stars. Our Sun resides about 30,000 light-years from the center of the galaxy.

Our Own Milky Way Galaxy Galaxies Our Own Milky Way Galaxy

The Milky Way (Artists’ Conceptions)

The Milky Way (actual photographs as seen from Earth)

Galaxies Our Own Milky Way Galaxy The individual stars of the Milky Way revolve around the galactic nucleus. The outermost stars revolve the slowest. Our Sun revolves around the galactic nucleus once about every 200 million years. A halo surrounds the galactic disk. The halo is spherical in shape and is composed of very tenuous gas The Milky Way’s halo contains numerous “globular clusters.”

Types of Galaxies The existence of galaxies other than our own was first proposed in the mid-1700s by Immanuel Kant. The are four basic types of galaxies in our known Universe: Spiral galaxies Barred Spiral Galaxies Elliptical Galaxies Irregular galaxies

Spiral Galaxies Spiral galaxies have “arms” extending from their nucleus. About 30% of all galaxies are spirals. They can have large diameters - up to 125,000 light-years. Spirals contain both young and old stars. The Milky Way may be a spiral galaxy.

The Andromeda Galaxy is an example of a large spiral galaxy.

Barred Spiral Galaxies In barred spiral galaxies, the stars are arranged in the shape of a bar. Barred spirals are generally quite large. About 10% of all galaxies are barred spirals.

A barred spiral galaxy

Elliptical Galaxies Elliptical galaxies have an ellipsoidal shape. About 60% of all galaxies are ellipticals. Most are smaller than spiral galaxies; however, they are also the largest known galaxies.

an elliptical galaxy

Irregular Galaxies Irregular galaxies lack symmetry. About 10% of all galaxies are irregulars. Irregulars contain mostly young stars Our local companions the Magellanic Clouds are irregular galaxies.

an irregular galaxy an irregular galaxy

Part 1 – Billions of Other Galaxies Exist in the Universe Video HTUW – Alien Galaxy Part 1 – Billions of Other Galaxies Exist in the Universe (6:07)

SLC Debrief (Notes should be taken during SLC Debriefs and kept in a section in your Science Binder) How old is our Milky Way galaxy? How many stars does the average galaxy contain? What’s in a galaxy? Who first discovered other galaxies beyond our Milky Way? How many galaxies are in the observable Universe? What unit of distance do we use when talking about galaxies? What is the largest galaxy even discovered, and how big is it?