# Physics 301 Astronomy Review Slides Fall 2012. What is Different About Astronomy? Incredible distances sizes periods of time.

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Physics 301 Astronomy Review Slides Fall 2012

What is Different About Astronomy? Incredible distances sizes periods of time

What is our place in the universe?

Earth orbits the Sun (revolves) once every year: at an average distance of 1 AU ≈ 150 million km. with Earth’s axis tilted by 23.5º (pointing to Polaris) and rotating in the same direction it orbits, counter- clockwise as viewed from above the North Pole.

We can recognize solstices and equinoxes by Sun’s path across sky: Summer solstice: Highest path, rise and set at most extreme north of due east. Winter solstice: Lowest path, rise and set at most extreme south of due east. Equinoxes: Sun rises precisely due east and sets precisely due west.

What determines the strength of gravity? The Universal Law of Gravitation: 1.Every mass attracts every other mass. 2.Attraction is directly proportional to the product of their masses. 3.Attraction is inversely proportional to the square of the distance between their centers.

Conservation of Energy Energy can be neither created nor destroyed. It can change form or be exchanged between objects. The total energy content of the Universe was determined in the Big Bang and remains the same today.

What does the solar system look like?

Properties of Waves Wavelength is the distance between two wave peaks Frequency is the number of times per second that a wave vibrates up and down wave speed = wavelength x frequency

What is the electromagnetic spectrum?

Chemical Fingerprints Each type of atom has a unique spectral fingerprint Observing the fingerprints in a spectrum tells us which kinds of atoms are present

Lines in a star’s spectrum correspond to a spectral type that reveals its temperature (Hottest) O B A F G K M (Coolest)

Fission Big nucleus splits into smaller pieces (Nuclear power plants) Fusion Small nuclei stick together to make a bigger one (Sun, stars)

Sunspots Are cooler than other parts of the Sun’s surface (4000 K) Are regions with strong magnetic fields

The brightness of a star depends on both distance and luminosity

Inverse Square Law for Light Luminosity passing through each sphere is the same Area of sphere = 4π (radius) 2 Divide luminosity by area to get apparent brightness Brightness is inversely proportional to the square of the distance from thr observor luminosity Apparent brightness = -------------------------- 4 π x distance 2

The relationship between apparent brightness and luminosity depends on distance: Luminosity Brightness = 4π (distance) 2 We can determine a star’s luminosity if we can measure its distance and apparent brightness: Luminosity = 4π (distance) 2 x (Brightness)

Temperature Luminosity H-R diagram depicts: Luminosity Temperature Color Spectral type Radius

We see our galaxy edge-on. Primary features: disk, bulge, halo, globular clusters

Background radiation from the Big Bang has been freely streaming across the universe since atoms formed at temperature ~3000 K: visible/IR. BIG BANG

VELOCITY Velocity = (the speed) + (direction) of the motion of mass. Expressed as a VECTOR QUANTITY MAGNITUDE expressed as distance/time (10km/hr) DIRECTION expressed in a direction (west) 30 km/hr west

Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles. What is Gravity?

What have we learned? What is the Sun’s structure? —From inside out, the layers are Core Radiation zone Convection zone Photosphere Chromosphere Corona Solar wind

Most massive stars: 100M Sun Least massive stars: 0.08M Sun (M Sun is the mass of the Sun.)

What happens to a star is determined by the amount of mass a star has. Low Mass (sun) High mass (Betelgeuse)

Some Other Stars on and Off the Main Sequence

Hubble Classifies Galaxies The Tuning Fork

Three Basic Types of Galaxies Spiral Variations exist within these three types. Elliptical Irregular