Introduction to Astronomy I know nothing with any certainty but the sight of stars makes me dream. - Vincent Van Gogh

This is big to us. Diameter of the Earth = 12,756 km The sun is much bigger. Diameter of the sun = 1,391,960 km ( 109 Earths across ) The farthest a human has traveled from the Earth is the moon, 283,000 miles (452,000 km) during the Apollo missions in the 1960’s and 70’s. The difference between a planet and a star involves their size. A planet is much smaller and shines only by reflecting starlight. A star is huge and produces its own light through a nuclear fusion reaction. However…

Distance from the Earth to the sun = 93,000,000 miles ( about 100 solar diameters) 1 Astronomical Unit ( 1 A.U.) 150,000,000 km = 1 Earth-Sun Distance Pluto is 3,673,500,000 km from the sun. ( 39.5 A.U.) Pluto The farthest distance traveled by an Earth spaceship (unmanned) is Voyager 1, which is now about 105 A.U. It was launched in 1970 and covers about 3.6 A.U. per year. Astronomical units (A.U.s) are used to measure distances between planets and their parent stars or other distances within the local neighborhood of a solar system.

Light years A light year is the distance light will travel in 1 year. A light year is a unit used to describe the immense distance between stars or galaxies. Stars are usually trillions of miles apart. Galaxies are millions of times further than that. Since light travels very quickly it can be used to measure the huge distances. Our sun is just another star. It is a little less than 8 light minutes away the Earth. The stars we see at night only look different to us because they are so much further away. Most of them are many light years away.

Light years A light year is the distance light will travel in 1 year. The speed of light is 300,000 kilometers per second. So…... 1 light year is 9,460,000,000,000 kilometers (approximately meters) Our nearest neighboring star is 4 light years away trillion kilometers. 1 Light year = 63,133 A.U. 1 year = 365 days x 24 hours x 60 minutes x 60 seconds = 31,536,000 seconds This would take 17,500 years in Voyager 1.

Our home galaxy, the Milky Way, is over 100,000 light years across. This spiral galaxy looks similar to our own. It is home to over 200 billion stars… many are larger than our sun. Each star represents its own solar system. You are here.

Our galaxy is called the Milky Way because on a dark night, far away from city lights, you can see a band of stars (and dust) stretching across the sky. Some think it resembles a river of milk across the sky. This is a picture of our galaxy (from the inside, of course) looking toward the center.

We cannot see our own galaxy from the outside because it would take millions years in our fastest spaceship to leave our galaxy so we could turn around and look back at it.

Galaxies come in many different shapes and sizes but they are all huge collections of billions of stars held together by gravity. Elliptical galaxy Spiral galaxy Irregular galaxy

From an edge-on view a galaxy would appear very thin with a central bulge and lanes of dust cutting across the middle. Clusters of stars form a halo surrounding the central bulge.

There are billions of other galaxies visible from Earth. This photo contains 10,000 of them and represents only a tiny fraction of the sky.

A galaxy is a massive collection of billions of stars and clouds of gas and dust held together by gravity. A nebula is a huge cloud of gas and dust that may be lit up by nearby stars. It is where new stars may form. Stars may form in massive clusters containing thousands or millions of stars. As nebulas collapse due to gravity new stars are created.

Stars come in many sizes and colors. The color of the star depends on its temperature. Small, dim stars are the hard-to-see red stars. The bright blue and white stars we see at night are the largest and hottest stars in the galaxy. Each star represents its own solar system.

Our sun is a medium-sized star. That means its brightness and surface temperature is average giving the sun its yellow color.

Stars verses Planets A star produces its own light and generates power by the process of fusion A planet cannot produce its own light (it shines only reflected light) and it orbits another object. Planets are much smaller than stars. The main difference between them is their size. Bigger means hotter. Mercury VenusEarth Mars Jupiter Saturn UranusNeptune Pluto Sun M V E M J S U N P My Very Eager Mother Just Sent Us Nine Pizzas

A solar system consists of a star (like our sun) and the objects that orbit around it (planets and their moons, comets, asteroids). Moons orbit planets and everything is held by the sun’s gravity. Asteroids are large leftover rocks (from boulder-sized to mountain-sized) that orbit the sun. Comets are dirty snowballs the size of mountains that melt as they fall toward the sun creating long tails lit up by sunlight.

Some planets are small and rocky, called terrestrial. These are like our home planet, Earth. Other planets are huge and made mostly of layers of gases, called gas giants. These, like Jupiter, were not big or hot enough to become stars, but they are still many time larger than the Earth.

Sizes Comets Asteroids Moons Planets Stars Galaxies

All energy travels in waves. 1 wavelength Since the human eye can only see a tiny fraction of these different wavelengths of electromagnetic energy, scientists must create different tools to observe different forms of energy traveling through the universe.

Types of Spectrum can be used to identify elements in stars and nebula from across the galaxy. Absorption spectrum has certain wavelengths of light absorbed leaving black lines which act as a fingerprint. Each element will absorb a specific pattern of colors. Emission spectrum is created when an element is heated to the point it emits a certain wavelength of light. Each element emits a different wavelength.

Spitzer Space Telescope Hubble Space Telescope Neutrino detector

This Neutrino detector is located deep underground where all other wavelengths of energy would be blocked. Neutrinos are tiny particles created by stars. They are so small they can travel right through normal matter, even through our entire planet.

By studying different wavelengths of energy we can learn different things about the universe around us. Infra red (IR)X-raySonar Ultrasound Ultraviolet (UV) Magnetic Resonance Image (MRI)

By combining images from different wavelengths of energy scientists can get a more complete picture.