Astronomy in the News• It turns out there is five times more material in clusters of galaxies than we would

expect from the galaxies and hot gas we can see.

• Most of the stuff in clusters of galaxies is invisible and, since these are the largest structures in the Universe held together by gravity, scientists then conclude that most of the matter in the entire Universe is invisible. This invisible stuff is called 'dark matter',

• There is currently much ongoing research by scientists attempting to discover exactly what this dark matter is, how much there is, and what effect it may have on the future of the Universe as a whole.

• http://ca.news.yahoo.com/scientists-close-mysterious-dark-matter-184251647.html

• http://www.usatoday.com/story/tech/2013/04/03/scientists-find-hint-of-dark-matter-from-cosmos/2049393/

• http://www.youtube.com/watch?v=BiSx9TzzLt4

Measuring Distance Beyond the Solar

System

Syste

9.1

Astronomical Units • In our Solar System, we tend to describe distances in terms of the

Astronomical Unit (AU

• astronomical unit (AU) is a measure of distance often used in astronomy

• AU = 149,597,870.700 kilometers

• Definition: An Astronomical Unit is the mean distance between the Earth and the Sun. In 2012, the International Astronomical Union defined the distance to be 149,597,870,700 meters (about 93 million miles).

• Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.

• The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.

• In terms of more common units of measurement, an astronomical unit is equal to the distance light travels in a little over eight minutes.

What is a Light Year• A light-year is a unit

of distance. It is the distance that light can travel in one year. Light moves at a velocity/speed of about 300,000 (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.

What is a Light Year• Why would you want such a big

unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the Universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.

What is a Light Year• Why would you want such a big unit of distance? Well, on Earth, a

kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the Universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.

• For distances to other parts of the Milky Way Galaxy (or even further), astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3 light-years. Using the light-year, we can say that :

• The Crab supernova remnant is about 4,000 light-years away.

• The Milky Way Galaxy is about 150,000 light-years across.

• The Andromeda Galaxy is 2.3 million light-years away.

Calculating the Distance to a Star in

Light Years• if the nearest red dwarf star is 4.01 x

1013 km from the Earth, what is its distance from Earth in light years.

• GIVEN: distance = 4.01 x 1013 km

• 1 light year = 9.46 x 1012

• REQUIRED: Distance to dwarf star in light years (ly)

Calculating the Distance to a Star in

Light Years• GIVEN: distance = 4.01 x 1013 km

• 1 light year = 9.46 x 1012

• distance in ly =

• 4.01 x 1013 km x 1 ly

• 9.46 x 1012

km

• distance of star = 4.24 ly

Light Years practice

• Practice

• Polaris is 5.05 x 1012km from Earth. Calculate the distance from Earth in Light Years.

The Light Year

• The farther a star is from Earth, the longer it takes for the light from the star to reach Earth.

• For example: the star Vega is approx. 25 ly from Earth. The light from Vega travels at the speed of light, which means that it takes the light from Vega approx. 25 years to reach the Earth.

Stellar Distance• The use of trigonometry to

determine distance

• Stellar Parallax is the apparent shift of close star in relation to distance stars that is caused by the change in position of the observer.

• the stars are not actually moving they just seem like they are because the person looking at them have moved to a different position.

• In other words, he is looking at them from a different angle.

Stellar Distance• Parallax is measured in angles.

• By measuring that angle, Scientist can calculate the distance. This method is know was triangulation.

• Triangulation uses the principle that if you know the length of one side of a triangle and the angles of two corners, you can calculate all the dimensions of the triangle.

Triangulation• astronomers use

triangulation to calculate the distance from Earth to a Star.

• The diameter of Earth’s orbit is the “known” side of the triangle.

• The star is then observed from two different positions in Earths orbit.

Triangulation• To do this, astronomers

observe the star and then wait 6 months to observe it again while Earth is at the opposite end of its orbit.

• the “triangle” formed by these observations can be used to calculate the distance to the star.

• With the help of telescopes, astronomers are able to use parallax to estimate the distances to stars as far as 100 ly away

What is Life?Does ET exist?

Questions• What kinds of things do you need to keep you alive?

• The Earth didn’t always have abundant water and nutrients easily available to living things. What are some ideas for how a good portion of Earth’s water and nutrients got here?

• We have to look for clues that collisions like these took place on Earth and in the solar system. What might evidence of a collision look like

Finding Life Beyond Earth

• http://www.pbs.org/wgbh/nova/education/space/finding-life-beyond-earth-collection.html