1. Made with help from: http://www.cosmos4kids.com/files/stars_intro.html
Stars: 19.1
Color
Composition
Classification
Made with help from:

2. How many stars are there?
Mini-Lab: Explore Activity:
How might scientists use this method to count the number of stars in the sky? Be thinking of that as you complete the activity:
Estimating the Number of Rice Grains
1. Take the sheet of black construction paper that has 2 inch squares. This represents the night sky
2. Spill a teaspoon of rice onto the black paper
3. Count the number of grains of rice in one square: record the number: ____________
Repeat this step with another square: ________
Repeat this step with 3rd square: ________
Repeat this step with 4th square: ________

3. How many stars are there?
4. Add the 4 squares together and divide by 4 (to get the average) record the number: ____________
5. Count the total number of squares on the piece of paper: _____
6. Multiply the number of squares _______ x your average _______ = ________
This will give you an estimate of the total number of grains of rice on the paper.
7. Count the grains of rice to get the “actual” total. record the number: ____________
8. How close were you based on your number from step 6? _____

4. How many stars are there?
Conclusion: How might scientists use this method to count the number of stars in the sky?

5. 1. Summer Meteor Shows

6. What is a star?
A star is an enormous, hot ball of gas held together by gravity.
The gravity is so strong that it causes nuclear fusion within the star.
Stars are the objects that heat and light the planets in a system.
Everything revolves around stars.
Thousands of stars cover our galaxy and when you look at our star, the Sun, you will see it is quite small.
Throughout the universe, there are big ones, small ones, and different colored ones.

7. What is a star?
A star is a huge ball of plasma, usually made of hydrogen (H) and helium (He).
That ball of fire also gives off light.
All kinds of light.
There are visible, infrared, ultraviolet, and X-rays constantly emitted into space.
You may find planets that are almost identical to the makeup of stars, like Jupiter, but something has not ignited their nuclear reaction.

8. The 3 Basics Astronomers look at three main characteristics of stars.
They study temperature, luminosity, and radius (size).
Each of these three factors can tell you a lot about a star.

9. Our Star: The Sun
As far as stars are concerned, the sun is rather small.
The yellow color tells you it has a nice, medium temperature.
The small radius also gives an indication that it not much of a powerhouse.
Last is the luminosity.
On Earth, the Sun may seem bright.
Compared to other stars it is only a candle.
Astronomers consider our Sun to be in the main sequence of its development.

10. Think about this… Blowtorch Candle Ember Which flame is hottest?
How are the colors different from each other?
There is a relationship between color and temperature. What do you think it is?

11. Color & Temperature Blowtorch Candle Ember
Turns out, blue means HOT and red means COLD.
Our blowtorch has the hottest flame, followed by the candle, followed by the embers.
This is backwards from what most of us believe.

12. Color & Temperature Stars are different colors too.
A star’s color depends on its surface temperature.
Very hot: blue
Hot: blue-white
Warm: yellow
Cool: Orange
Very cool: red
Bluer stars have a higher surface temperature.
Lower temperature stars give off a lot of red light.

13. Luminosity
Luminosity is the total amount of light given off by a star.
Brightness, or intensity, measures the amount of light reaching Earth.
This is an important difference…the distance of a star makes a HUGE difference in its brightness.
How bright a star seems to us is its apparent magnitude.
The absolute magnitude refers to the actual brightness

14. Luminosity is caused by…
There are some specific factors that affect luminosity.
As the size of a star increases, luminosity increases. If you think about it, a larger star has more surface area. That increased surface area allows more light and energy to be given off.

15. Luminosity is caused by…
Temperature also affects a star's luminosity. You don't even need to look at a star for this idea.
Just think about a stove, or a fire. When an electric stove is off, it is black.
But when it is on high, the stove glows bright red.
The same idea applies to stars. As a star gets hotter, the number of nuclear reactions increases.
More reactions, more energy.

16. 2. Cool Stars

17. Classification of Stars
When scientists first started to study stars, certain differences became noticeable.
They had different colors, different intensities, and even different movement.
The time had come to develop with a system of classification for stars.
Science has always used different forms of classification when it studies natural phenomena.

18. Classification of Stars
Astronomers classify stars by their temperature.
Temperature determines much of the activity of a star.
You can even figure out how old it is when you know the temperature.
Astronomers at Harvard College Observatory came up with the system and applied letters to each class.
Some of the letters are O, B, A, F, G, K, & M.
“Oh Be A Fine Girl/Guy, Kiss Me!”

19. Classification of Stars
The "O"s are the hottest with temperatures over 25,000 Kelvin.
The cooler stars are at the other end of the list with "M" stars at less that 3,500 Kelvin.
As a reminder, water boils at 373 Kelvin.

20. Special Stars Not all stars have solar systems spinning around them.
Some stars are just sitting out in the middle of nowhere.
Some stars have a companion star nearby, kind of like a twin.
When you have a twin, astronomers call you a binary star.

21. 3. A star with Spiral Arms

22. Special Stars: Giants Really, really, really big stars
Some can be seen without a telescope
There are 2 types:
Blue Giants: really hot & massive
Red Giants: Cool & massive - these guys are big because they are cooling down and expanding
A supergiant is a super massive star

23. 4. The most gigantic stars

24. Special Stars: Dwarfs Smaller stars There are 2 types: Dwarfs:
about the size of a smaller planet
Sirius B, the largest known Dwarf star, is slightly smaller than Earth
White Dwarfs are small hot stars
Neutron Stars:
even smaller, diameters of about km (12-18 miles)
A Pulsar is a spinning neutron star that sends out beams of radiation

25. Can we organize all of this together?
Yes! In the early 1900s, the Danish astronomer Ejnar Hertzsprung & American astronomer Henry Russell developed an important tool for studying stars.
They made a graph that showed the temperature on the x-axis and the luminosity on the y-axis.
This graph is called the Hertzsprung-Russell, or H-R, diagram.
Each dot represents a star with a given temperature & luminosity.

26. 5. The HR Diagram & Globular Cluster

29. The H-R Diagram! What’s so special about this diagram?
It gives you a TON of information.
List 5 things that it tells you about a star:
Spectral Type (O, B, A, F, G, K, M)
Temperature
Luminosity/ Brightness
Size
Type of star (red giant, white dwarf, etc.)

30. 6. The HR Diagram

31. Virtual Lab: Star Composition and H-R Diagram Placement
The goal of this lab is for you to become familiar with the HR Diagram and HOW to use it!
The link for completing this lab is on my web site.