The Milky Way

1. The Milky Way Our Galaxy

2. If you think of the street you grew up on as our Solar System, then the Galaxy we are in would be like the entire planet Earth. But not exactly – there may be millions of streets on our planet, but there are billions of solar systems in our Milky Way galaxy! Our Solar System, as large as it is, only occupies a teeny tiny fraction of space in a small, average corner of our galaxy. Our Sun, so dominating to us, would be indistinguishable in the mists that are comprised of millions of other neighboring “suns” (and other stuff) in our arm of the Milky Way. Please Note: A portrait such as this one of the Milky Way Galaxy does not exist to us– and probably never will. WHY?

3. You and I can indeed directly view the Milky Way galaxy however....... When you look up into the night sky with your naked eye, binoculars, or even a powerful telescope, you are gazing within our own galaxy. Every single star you see is, in fact, a member of the Milky Way galaxy. Additionally, on a clear night in a dark area, you will notice a glowing band streaking overhead. You are actually staring back into the center of our galaxy from our place on the edge. This haze is actually a high concentration of stars called the central bulge of our galaxy.

4. -The Milky Way galaxy is thought to be about 13 billion years old -Estimates say that it contains anywhere from 200-400 billion stars -It measures about 100,000 light years across -It is a spiral structure with 4 major “arms” loosely radiating and swirling from the center -The entire galaxy is moving through space at over 500 km/s -Objects in it rotate at over 200 km/s, taking us 250 million years to orbit the center once -A philosopher – E.Kant (1755), was perhaps the very first to suggest its existence, what it was, and our place in it -Believe me...You don’t want to know how the name “Milky Way” came to be.... FACT FILE

5. As you would imagine, stars come in variety of sizes, colors, temperatures and compositions. They do however have much in common.... Stars 101 Star– A large mass of gas – mainly hydrogen, collected into a sphere by the force of gravity which is thus superheated (plasma) by nuclear fusion. Hydrogen is slowly converted into Helium as the star caries out its life cycle. Stars are classified in many ways – mainly by temperature, size, age, brightness, and color. Our Sun (Sol), is quite average and common – a G2V yellow dwarf. Such classifications help scientists to compare and evaluate stars in our galaxy.

6. The vast data needed to classify stars is gathered mainly from the spectral analysis of light and energy emitted by stars – no matter how distant. The light produced by every single star is unique. The temperature of the star, its luminosity, its chemical composition, and it’s motion too, will all have effects on the light that it produces, and these effects can be decoded by examining the star’s spectrum. We see the Sun’s spectrum (albeit in a very coarse form) whenever we look at a rainbow, or use a prism to split sunlight into its constituent colors. Starlight, too, is composed of these seven colors, but the relative intensities of light along the spectrum will vary considerably from star to star. The closest star to us (other than our Sun, of course) is a Red Dwarf called Proxima Centuariand is 4.2 light years away. Did you know... Using our most advanced propulsion system to date, it would only take you 80,000 years to reach our closest neighbor! Yay!

7. The Life and Death of a Star The birth of a star begins within huge clouds of gas and dust. As the cloud collapses, temperature and density increases.Such clouds are referred to as Nebulae. Types and Examples: NGC 1977-Reflective Nebula also in Orion M42- Emission Nebula in Orion IC 434– Dark Nebula in Orion Some stars remain for a very long time. Stars similar to our sun have a lifespan of around 10 billion years. Stars with higher masses tend to lead far shorter lives – millions of years “only”.

8. Betelgeuse in Orion is an example of a star in the Red Giant stage The brightest star in our night sky, Sirius A, is an example of a star in the White Dwarf stage There are no examples of stars in the Black Dwarf stage because none exist. Why? Planetary Nebulas come in a variety of interesting colors and patterns. All however are in a spherical shape.

9. 600 light years away and 10,000 times brighter than our sun, Antares is an example of a star in the Red Supergiant stage. Eventually, Antares and other large mass stars will explode creating a flash that can be seen across the universe. In our galaxy, it is estimated that a supernova occurs every 50 years or so. Astronomers identify sites of past supernovae by the remnants left behind from the explosion. This nebula was created after a supernova in 1054 AD. Somewhere inside is the original star – now called a Neutron Star. These are very small and very dense: 1 teaspoon would weigh 1 billion tons here on Earth!

10. A lot of times neutron stars rotate at a very consistent rate - this spin is actually what allows something so small to become detectable even at a very great distance…… A stream of powerful radiation is emitted much like a lighthouse shines out a beam of light. This “flashing” is what alerts us of it’s presence in the galaxy.

11. Only the largest mass stars might produce Black Holes when they end their life. Black Holes are even denser than Neutron Stars. Once only a hypothetical structure, Black Holes have since been proven to exist with direct evidence. If something is invisible, how do we know it exists? A black hole exerts so much gravity that, once it falls in, nothing can escape – not even light. We know they’re there by watching the behavior of matter in the area around black holes as it is effected by this tremendous gravity.

12. As material from near by stars spirals into a Black Hole it becomes super heated – giving off a large amounts of radiation we can detect from Earth. Sometimes unimaginable energy is released as Jets while matter enters a Black Hole. These Gamma Ray Bursts (GRB’s) can be seen from across the universe.

13. Interstellar Space is the term used to describe the virtually empty space in between stars. Stars are typically very far apart – but there are exceptions. A Constellation is a widely spaced pattern of bright stars as viewed from Earth. Historically, humans have recognized constellations as a way to break up the sky into sections. Lonely and imaginative people from long ago have assigned personalities to these shapes. Some Recognizable Constellations.... Orion “The Hunter” Ursa Major “The Bear” Auriga “The Charioteer” Leo “The Lion”

14. Looking deeper into the night sky, stars are seen in many unique formations..... Close The Pleides A close grouping of stars is called an Open Cluster. They are usually made up of a few hundred stars and are relatively young objects. Closer M22 A Globular Cluster is a dense, older population of up to millions of stars. Really Close M40 A Binary System has 2 stars gravitationally locked together. They are difficult to visually recognized because the brighter star usually outshines it’s companion

15. Stars appear to move throughout the night. A constellation noticed just above the horizon just after sundown may soon be overhead when you go out later that night. Like the Sun, stars rise in the east and set in the west Instead of pin points of light, stars look light streaks in this photograph. Why is that? We, of course know, that is not the Sun and Stars that move but rather us. As the Earth rotates we get a different view continuously.

16. Astronomers often refer to the “magnitude” of an object in the sky. This is a fancy way of classifying it’s brightness as seen from Earth. Magnitude - A number based on a scale where the lower a number is, the brighter an object is. For example, the stars within the constellation Orion can be compared by their brightness or magnitude. If you were looking up at Orion, which star would you expect to be the brightest? Interesting Facts: Our Sun has a magnitude of -28.6 The Full Moon is at -12.6 Venus = -4.4 Pluto = 14 Sirius (the brightest star in the sky) = -1.4 *With a naked eye, most people have difficulty seeing objects beyond a magnitude of 6. With good Binoculars maybe 9. The Hubble telescope can image something as dim as 30.

17. PARALLAX 0 1 2 3 4 5 6 7 8 9 10 **Using Trigonometry along with observations to calculate the distance of stars!