Characteristics of Stars

Distances and Size Magnitude Elements Mass and Temperature

Distances and Size The Astronomical Unit is used within the solar system It is 93 Mmiles or the distance from the Earth to the sun

Distances Kilometers ( or miles) can be used to measure the sizes of planets

Distances and Size The sun is the standard unit for the size of stars

Distance and Size Sirius is 2.5 suns and Pollux is 4 suns in size

Distances and Size Betelgeuse is 1000 suns in size

Distance and Size The distances to stars can be measured by  Light years The distance light travels in 1 year 300,000 km/sec  This is 9.5 trillion km in 1 year  Proxima Centauri is 4.2 ly away or 39,900,000,000,000 km or 24.8 trillion miles  The circumference of the Earth is ~25,000 miles  Parsecs 3.26 ly When a star is this far away it starts showing parallax Distances to stars are also measured in parsecs

Parallax Explained (Do Not Write This Slide Down… Just Read And Try) Parallax measurements take advantage of the fact that, as the Earth orbits around the Sun, relatively near-by stars appear to move with respect to the fixed, very distant stars (see the diagram below). This is the same thing that happens when you look at a close object with first one eye and then the other. For example, hold your thumb at the tip of your nose. Look at your thumb with first your right eye and then your left. Your thumb appears to move because your eyes are not at exactly the same place, so each eye views the thumb from a different angle. Now hold your thumb at arm's length and repeat the experiment. Your thumb will still appear to shift, but will not appear to move as much as it did when it was closer. The same thing happens to stars. The closer stars appear to shift more than the farther stars. The "fixed" background stars are not really fixed; they are just so far away that we cannot distinguish their apparent shift. The apparent shift of the stars is called their parallax.

Parallax

Parallax Continued (2 Examples) How we came up with a parsec The wider the angle, the closer the star 3.26 light years = 1/3600 of a degree

km, parsec, AU, light year, meter Put these distances in order from smallest to largest km, parsec, AU, light year, meter (Smallest)  Meter, km, AU, Light Year, Parsec  (Largest)

Magnitude (the brightness of a star) Apparent Magnitude Luminosity Absolute Magnitude

Apparent Magnitude How bright a star appears to be Dependent on  Distance from Earth  Not standardized  Does not reflect a star’s true brightness

Luminosity The actual brightness of a star Depends on  Size Bigger = Brighter  Temperature Hotter = Brighter If 2 stars were the same size but star A was 6000º=C and star B is 10,000ºC, which one would be brighter?

Absolute Magnitude The way astronomers express true brightness or luminosity  How bright the stars are if they were lined up 10 parsecs away from Earth  Depends on Size and Temperature  The more negative a # the brighter the star

Absolute Magnitude Put these stars in order from brightest to dimmest (1=brightest 4=dimmest) Antares: Procyon:+2.62 Spica: Sirius: ** Look at the chart on 623. Which star has the brightest apparent magnitude?

Elements By now you should know how scientists determine what elements are in stars  (comparing emission and absorption spectra!) Hydrogen and Helium are found in the greatest quantities All of the other elements are found in various amounts No 2 stars have the same exact make-up of elements

Mass and Temperature Mass – Difficult to measure  Observations such as gravitational influence are used to determine this  Compared to sun (like size) Temperature – determines the color

Temperature and Color Blue stars are hotter  Blue light has a shorter wavelength, this means it has more energy Red stars are cooler  Red light has a longer wavelength, this means it has less energy COOL HOT

What are the characteristic of stars? 1. Distance and size 2. Magnitude 3. Elements 4. Mass and temperature 5. All of the above

What is an Astronomical Unit (AU)? 1. Distance from Moon to Earth 2. Distance from sun to The Moon 3. Distance from sun to Earth 4. Distance from Earth to Proxima Centauri

What is a light year? 1. The distance light travels in one month ,000 km/sec 3. The distance light travels in one year 4. Both 2 and 3 5. All of the above

What is a parsec? ly (light years) 2. The distance from sun to Earth 3. The distance light travels in one year 4. A measure of time

Parallax helps scientists… 1. Figure out the distances of stars from Earth 2. Figure out the temperature of stars 3. Figure out the size of stars 4. Figure out the brightness of stars

A parsec is larger than a light year 1. True 2. False

Absolute magnitude is… 1. How bright a star appears to be from Earth 2. The actual brightness of a star 3. How bright the stars are if they were lined up 10 parsecs away from Earth (True brightness)

Apparent magnitude is… 1. How bright a star appears to be from Earth 2. The actual brightness of a star 3. How bright the stars are if they were lined up 10 parsecs away from Earth (True brightness)

Luminosity is… 1. How bright a star appears to be from Earth 2. The actual brightness of a star 3. How bright the stars are if they were lined up 10 parsecs away from Earth (True brightness or luminosity)

Red stars are hotter than blue ones 1. True 2. False