Download presentation
Presentation is loading. Please wait.
Published byAmber Franklin Modified over 9 years ago
1
A105 Stars and Galaxies Today’s APOD News Quiz Today
Jewelbox homework due Thursday
2
Announcements… Kirkwood Obs. open Weds night 8:30-10:30 PM
Rooftop Sessions, Oct. 10 & 11, 9:00 PM Remote Obs Oct. 10 PM and Oct. 7 AM
3
The Sun Today Image credit: Solar Orbiting Heliospheric Observatory/MDI Not very interesting today!
4
Stars Basic Properties of Stars distance brightness diameters
The Hertzsprung-Russell Diagram
5
The Brightness of Stars
Apparent brightness – how bright does it look in the sky? Absolute brightness – how bright is it really?? The apparent brightness depends on both a star’s distance and its intrinsic brightness
6
The Inverse Square Law tells us how a star’s apparent brightness changes with distance
Brightness decreases as distance squared something twice as far away will be four times fainter something 10 times further away will be 100 times fainter something 1000 times further away will be a million times fainter
7
How Far Away Are Stars? brightness changes as 1/distance2
If we know a star’s apparent AND absolute brightness, we can calculate its distance brightness changes as 1/distance2 The inverse square law describes how the brightness of a source light (a star!) diminishes with distance But how do we get the distances to stars whose brightness we DON’T know?
8
Measuring the distances to stars using Parallax
9
Measuring the distances of stars
11
Parallax : apparent change in the position of an object due to a change in the position of the observer Stellar parallax uses the Earth’s orbit as the baseline Parallax
12
What is a Parsec??? Parsec: the distance to an object
with a stellar parallax of one arc second A star at a distance of 1 parsec shows a parallax of 1 arc second How big is one arc second? 1 parsec = 3.26 light years The size of a dime at a distance of 2.3 miles! A parallax of ~0.001 arc seconds is the smallest we can measure The parallax of Alpha Centauri = 0.76 arcseconds
13
How Big Are Stars? From its COLOR!! Luminosity depends on….
We can’t see the stars’ diameters through a telescope. Stars are so far away that we see them just as points of light. How Big Are Stars? If we know a star’s temperature and its luminosity, we can calculate its diameter. From its COLOR!! How do we determine a star’s temperature? Luminosity depends on…. TEMPERATURE - the hotter a star is, the brighter it is. DIAMETER – the bigger a star is, the brighter it is. Stars range in size from about the size of the Earth to hundreds of times the Sun’s diameter
14
Magnitudes Astronomers use “magnitudes” to describe how bright stars are Small numbers are brighter, large numbers fainter. The brightest naked-eye stars are around magnitude zero. The faintest naked-eye stars are around magnitude six 5 magnitudes are a factor of 100 in brightness (a 6th magnitude star is 100 times fainter than a 1st magnitude star)
15
Stars come in many sizes and colors
But only certain sizes and colors are allowed! Stars come in many sizes and colors HR Diagram Simulator
16
Key Ideas – The HR Diagram
The intrinsic brightness or luminosity of stars depends on temperature and radius if two stars have the same radius, the hotter one is brighter if two stars have the same temperature, the bigger one is brighter The Hertzsprung-Russell Diagram relates the temperature and brightness of stars
17
The sun is an ordinary, yellow main sequence star
The Main Sequence The sun is an ordinary, yellow main sequence star BRIGHTNESS TEMPERATURE
18
Giants and Supergiants are cooler and very large
BRIGHTNESS White dwarfs are small and hotter TEMPERATURE
19
Most stars occur in these main groups in the luminosity-temperature diagram
Main Sequence Giants Supergiants White Dwarfs BRIGHTNESS TEMPERATURE
20
Quiz: Which star is the biggest?
D BRIGHTNESS TEMPERATURE
21
Quiz: Which star is the smallest?
B C D BRIGHTNESS TEMPERATURE
22
The Nearest and the Brightest
Goal: to learn about types of stars to explore the stars near the Sun and compare them to the stars we see in the sky Task: plot a Hertzsprung-Russell diagram including both the nearest stars and the brightest stars in the northern sky
23
Familiar Stars
24
1000 ly A little farther out
25
The Brightest Stars in the Sky
Distance (LY) Temperature (K) Absolute Magnitude Sun 5800 4.8 Sirius 9 9600 1.4 Canopus 232 7600 -2.5 Alpha Cen A 4 4.4 Arcturus 37 4700 0.2 Vega 25 9900 0.6 Capella 42 5700 0.4 Rigel 773 11000 -8.1 Procyon 11 6600 2.6 Achernar 144 22000 -1.3 Betelgeuse 427 3300 -7.2 Hadar 335 25000 -4.4 Acrux 321 26000 -4.6 Altair 17 8100 2.3 Aldebaran 65 4100 -0.3 Antares 604 -5.2 Spica 263 2600 -3.2 Pollux 34 4900 0.7 The Brightest Stars in the Sky (no need to copy these down!)
26
Plot Absolute Magnitude vs. Temperature
27
The Nearest Stars
28
The Nearest Stars Star Distance (LY) Temperature Absolute Magnitude
Prox Cen 4 2800 15.53 Alp Cen A 5800 4.4 Alp Cen B 4900 5.72 Barnard’s 6 13.23 Wolf 359 7.5 2700 16.57 Lal 21185 8 3300 10.46 Sirius A 9 9900 1.45 Sirius B 12000 11.34 Luyten 726-8A 15.42 UV Ceti 2600 15.38 Ross 154 10 3000 13.14 The Nearest Stars
29
Adding the Nearest Stars to the HR Diagram
30
The HR Diagram Giants and Supergiants Main Sequence White Dwarf
31
Key Ideas – Stellar Census
Comparison of Main Sequence, Giant, and White Dwarf Stars The Family of Stars What are the most/least common kinds of stars? Why are red dwarfs so common?
32
The brightness of a star depends on distance, luminosity, and temperature
33
Most luminous stars: 106 LSun Least luminous stars: 10-4 LSun (LSun is luminosity of Sun)
34
Most massive stars: 100 MSun Least massive stars: 0.08 MSun (MSun is the mass of the Sun)
35
Main-Sequence Star Summary
High Mass: High Luminosity Short-Lived Large Radius Blue Low Mass: Low Luminosity Long-Lived Small Radius Red
36
Stellar Properties Review
Luminosity: from brightness and distance 10-4 LSun LSun Temperature: from color and spectrum 3,000 K ,000 K Mass: from binary-star orbits 0.08 MSun MSun
37
Constructing an HR Diagram
38
What’s this B-V color? Astronomers measure the brightness of stars in different colors Brightness measured in blue light is called “B” (for “Blue”) Brightness measured in yellow light is called “V” (for “Visual) Astronomers quantify the “color” of a star by using the difference in brightness between the brightness in the B and V spectral regions The B-V color is related to the slope of the spectrum
39
The slope of the spectrum is different at different temperatures
Remind students that the intensity is per area; larger objects can emit more total light even if they are cooler.
40
Homework #7 Due THURS. Events this week For This Week...
Rooftop Oct 10 & 11 Kirkwood Open Night Oct. 11 Remote Observing Oct 14 & 16
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.