Dec. 19 – Stars

Stars

Learning Goals: Understand that stars come in different types.

Success Criteria: You can describe the life cycle of different stars.

Stars come in many different sizes, colours and temperatures.  Here are a few ways we can tell the difference between stars.

Luminosity

• Total amount of energy produced by a star per second.
• The sun has luminosity of 1.

Apparent Magnitude 

• A star's brightness as seen from Earth.
• The sun = -27 apparent magnitude
• Full Moon = -13
• Brightest Stars = 1
• dimmest stars = 6

Absolute Magnitude

• The magnitude we would see if we were 33 ly away.

Colour

• A star's colour is related to temperature.
• Blue - hotter
• Yellow - medium
• Red - cooler

Spectrum 

• The rainbow of light emitted by a star.  
• Missing lines in the spectrum tell you what the star is made of.

Each element emits a different spectrum.  The missing colours (dark bands) line up with hydrogen, so the star definitely has hydrogen in it.

Mass

• The sun is 2 e 30 kg = 1 solar mass
• Most stars range from 0.1 to 120 solar masses.

The life cycle of stars

Nebula - a massive cloud of gas and dust.

Protostar - dust from a nebula collapses under gravity.

After millions of years, a protostar collapses further until fusion happens, 15 million °C.

The type of star depends on mass.

Hertzsprung-Russell Diagram

 - hot, luminous stars are more massive.

 - most stars fall on "Main Sequence"

Small stars:

After 10 billion years, burn off hydrogen and expand to become red giants.

hydrogen --> helium --> other elements (lithium, carbon, etc)

Eventually stops fusion and a white dwarf is left over.  Cool down and fade out.

Bigger Stars:

Shorter lives, burn faster.

Can fuse heavier elements

carbon --> iron

After fusion, gases collapse, then bounce back and explode into a super nova.

The Crab Nebula is the left over from a super nova.

Heavier elements are fused.

After super nova you can have one of two things left over...

Neutron Star - made of pure neutrons.

Super dense, gravity 300 000 times that of earth.

This is what Neutron Star would look like over Vancouver.  Much smaller than the Earth, but hundreds of thousands of times more massive.

Black hole - even more dense than neutron stars, gravity so strong that light cannot escape.

An artists drawing of a star being torn apart by a black hole.

The life cycle of different stars.

Homework

• P. 351 # 1, 2, 6, 7, 9
• P. 369 # 1-3, 6, 7, 8, 11

Dec. 18 – Satellites and Distances

Unfortunately it was too cloudy last night for you to make use of your star finders.  Hold onto them and try them out over the holidays.  One day we might get a hight without snow!

Learning Goals: 

• Understand the basic functions of satellites.
• Understand how astronomical distances are described.

Success Criteria:

• You can describe how satellites orbit and describe some major uses of artificial satellites.
• You can convert between kilometers, astronomical units and light years.

The Earth has one natural satellite... the Moon.

But there are many artificial satellites that are made by humans.

These satellites provide us with many useful functions:

Uses of artificial satellites.

• Spying
• Communication (phones, radio, tv)
• GPS (Global Positioning System)
• Weather
• Maps
• Scientific Research
• International Space Station (ISS)

Chris Hadfield is a Canadian astronaut who was the commander of the ISS earlier this year. 

While Commander Hadfield was up on the International Space Station he took many photos and made many videos which he posted online.  Here's one of them:

How does the ISS and other satellites stay in orbit?

- They move at a specific speed to stay in orbit.

- They are constantly falling, but never reach the Earth.

Types of orbit.

 - The higher the altitude the longer the orbit.  The ISS is 350 km up and orbits in 90 mins.

    -  Low Earth Orbit (under 2000 km)

        eg. Polar Orbit

    -  Medium Orbit (under 35 000 km)

        eg. GPS satellite in geostationary orbit (24 hr period)

     - High Elliptical Orbit (over 40 000 km)

CHAPTER 9: Beyond our Solar System

The Moon is about 384 400 km away from the Earth.

Earth is about 150 million km away from the Sun.

  1.5 e 8 km = 1 AU (astronomical unit)

• Mars is 1.5 AU from the Sun.
• Jupiter is 5.2 AU from the Sun.
• Pluto is about 30 AU from the Sun.

The nearest star to the sun is Proxima Centauri.  It is 4.0e13 km away from the sun, about 270 000 AU.  Clearly we need a unit that is even larger than AU.

Light Years

Light travels at a speed of 

300 000 km/s.  How far does light travel in one year?

300 000 km/s x (60 s/min) x (60 min/hr) x (24 hr/day) x (365 days/year) x (1 year)

    =  9.46 e 12 km

This is one light year.

How many light years away is Proxima Centauri?

Here's how you do the calculations:

For some comparison, Polaris is 400 ly away.

The closest galaxy to the Milky Way, Andromeda, is 2 600 000 ly away!

Here are some other distances,

How do we measure these distances?

Parallax - apparent change of position due to location.

We can use the apparent change in position to triangulate the distance.

Homework:

• P. 343 # 1-5, 7-10

Dec. 17 – Constellations

Learning Goals:

• Understand some cultural significances of astronomy.
• Understand how to describe were celestial objects are in the sky.

Success Criteria: 

• You can describe how the solstice, equinox and constellations are significance in different cultures.
• You can find certain constellations in the sky.  You can describe where they are on the celestial sphere.

Handout:

• Constellations

Today we started by discussing how people from different cultures saw different time of year or different things in the sky as significant.

The shadows create the shape of a serpent on the side of a Mayan pyramid during the equinox.

Stonehenge was built to align with the setting sun on the exact day of the summer solstice.

The Egyptians built their pyramids with air shafts that aligned with significant stars.

People throughout history have named and assigned meaning to the stars.  They are grouped together in what are called constellations.  These constellations change over the course of 100 000 years due to the motion of individual stars.

The Big Dipper is an example of a constellation.  In fact, it's actually part of a larger constellation called Ursa Major.

It is important to note that these constellations are arbitrary.  Some people might see a hunter called Orion, while the some Aboriginal people call the same set of stars a canoe.

   

One way to describe where things are in the sky is to use angles called azimuth and altitude.

Another way is to use the celestial sphere.

An imaginary sphere around the Earth where we can project all celestial objects.

While the stars will be stationary on the celestial sphere over the course of our lifetime, planets and the sun appear to move past the stars due to our own motion of the Earth.

People name different time of the year after certain constellations depending on where the sun is.  These twelve constellations are called the Zodiac.

 Sometimes planets appear to move backwards in their path in a phenomenon called retrograde motion.  This happens because the Earth moves faster than Mars.

Retrograde motion of mars.

We then made our very own star finders!  You can download and make your own versions from various sites such as these:

• http://www.star-finder.ca/print.html
• http://wbplanetarium.weebly.com/how-to-use-a-star-finder.html

Those of you who are more high tech can download apps on your phones to do the same thing.  Here is a fun one that finds planets for you, but there are many more that do the same thing.

• https://itunes.apple.com/ca/app/planets/id305793334

When you are at home, try using google sky to view the constellations, galaxies and other objects in our night sky:

• http://www.google.ca/sky/

Homework:

• P. 333 # 1-7
• Go out and use your star finders!  Look for Orion and the North Star, Polaris.

Dec. 13 – The Sun, Earth and Moon

Learning Goals: Understand the parts of the sun.  Understand the motion of the Earth and Moon.

Success Criteria: You can describe the parts of the sun.  You can describe the motion of the Earth and Moon and use it to explain the seasons, length of day, eclipses, and the tides.

Handout: The Motion of Earth and the Moon

Yesterday someone asked what would happen if two galaxies collided into each other.  Here's a video of what would happen.  This is a simulation that was calculated by computers.

We started by sketching our own pictures of the sun.  here's an image showing all the layers.

We also discussed sunspots, solar flares and solar prominence.

Sunspots!

Solar flares.

 Then we talked about how the magnetic field protects us from harmful particles that come from the sun.  The particles are pushed towards the North or South poles and when they hit the atmosphere, we see it as the Aurora Borealis (northern lights) or Aurora Australis (southern lights).

Then we talked about which direction the Earth rotates:

It rotates this way!

Looking down from the North Pole, the earth rotates counter-clockwise.  It also moves in a counter-clockwise motion around the sun.

We then discussed Heliocentric (sun at centre) and Geocentric (earth at centre) views of the solar system.  Today we know that Copernicus and Galileo are correct and the Earth indeed goes around the sun.

We discussed how the tilt of the Earth causes the seasons:

And how this tilt is constantly changing.

Then we looked at phases of the moon:

... eclipses ...

and tides...

Quite a lot for one days work!

Homework: Study for the Ecology Unit Test on Monday!

Dec. 12 – Astronomy

New Unit: Astronomy

In this unit we are are looking at all the wonderful amazing objects in our sky.  Check out this site to have a look at the size of our universe: http://htwins.net/scale/

Learning Goals: Understand the basic makeup of our solar system.

Success Criteria: You can name the planets and their relative sizes as well as other celestial objects in our solar system.

On a clear night far away from the city, you can see the "Milky Way", our galaxy.

Here are some definitions you should know:

Astronomy - Study of what is beyond the Earth.

Celestial Object - object in space.

Universe - everything that exists.

There are galaxies as far in our universe as we can see.

Galaxy - a collection of billions of stars, planets, dust and other celestial objects

"Milky Way" - our galaxy

Stars - a massive ball of gas (plasma) that emits a huge amount of energy.

Our closest star, the sun.

Planet - a large spherical object that travels around a star and dominates its orbit.

The relative sizes of the planets.

At this point I gave everyone a piece of blank paper and we all drew the planets in our solar system at the correct relative sizes.

Dwarf Planet - a large spherical object that travels around a star and does not dominate its orbit.  Pluto is one of many dwarf planets that have been discovered.

Orbit - closed path of one object around another.

Satellite - an object that orbits a planet.

Asteroid - a celestial object too small to be a planet.

Meteoroid - smaller than asteroids.  When they crash into our atmosphere, we see them as shooting stars.  The larger ones can cause something like this...

Comet - a chunk of rock and ice that travels on long orbits around the sun.  Parts of comets get burnt off by the sun and leave a tail pointing away from the sun.

Homework: P. 308 #1 – 7