Transcript Star Facts - Dr. Noha MH Elnagdi

Our Universe
Stars
Colors and Temperatures
Blue
Hottest
Yellow
Medium temperature
Sun
Red
Coolest
Different Types of Stars
A. Giants
D. Supergiants
B. White Dwarfs
E. Sun
C. Main Sequence
Sagittarius Star Cloud, HST
Star Color

Stars have different colors
Some look red (like Betelgeuse), some
look more yellow (like the Sun), and some
look blue or blue-white (like Sirius)
Color is directly related to temperature

Light is not sensitive to the details of
the star's composition but to its
temperature
(according to which law?)

Astronomers can determine:
1. the surface temperature of a star by
measuring its color
2. the composition of its outer layers by
looking at its spectral lines
Sun
Star color and brightness
Is a star’s
color
(temperature)
related to its
size?
 Is the relation
the same for
all stars?
 Are there
different
kinds of
stars?

Electromagnetic Radiation

Energy that travels
through space in
waves
 Stars give off
electromagnetic
radiation in different
forms
 Each form has its own
wavelength

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



Radio Waves
Infrared Rays
Visible Light
Ultraviolet Light
X-Rays
Gamma Rays
Continuous spectrum and
Absorption spectrum
 A Any
visible white light consists of millions
of colors, including the seven very obvious
colors: red – orange – yellow – green –
blue – indigo and violet.
 A hot glowing object like a wire inside the
bulb gives off a continuous spectrum.
 A continuous
spectrum is a spectrum that
shows all colors.
Continuous Spectrum
 A rainbow
is an example of a continuous
spectrum. Most continuous spectra are
from hot, dense objects like stars, planets,
or moons.. Any solid, liquid and dense
(thick) gas at a temperature above
absolute zero will produce a thermal
spectrum.
Absorption Spectrum
 Because
each element in this world
absorbs a color or more of the continuous
spectrum, the elements in the atmosphere
of a star emits an absorption spectrum
rather than a continuous spectrum.
 A absorption spectrum is produced when
light from a hot solid or dense gas passes
through a cooler gas (which is the
atmospheric gases of the star in this case)
Measuring the chemical
composition of a star from its
absorption spectrum
Identifying the
composition of star’s
atmosphere using its
absorption spectrum
Composition of a typical star
 Here
are spectra for some elements
common in the atmospheres of stars:
•In a star, these elements absorb light at their special frequencies. On
the following pages, you will see both the elements for comparison
and a star's spectrum. Your job is to identify all the elements you can
detect in the star's atmosphere.

Here are spectra for some elements common in the
atmospheres of stars:
Here is the spectrum of a mystery star:
Which elements are present?
 Yes,
you are correct!
 The mystery star:
 has the following elements.
 Hydrogen
 Iron
Here are spectra for some elements common in the atmospheres of stars:
Here is the spectrum of a mystery star:
Which elements are present?
 Yes,
you are correct!
 The mystery star:
 has the following elements.
 Calcium
 Hydrogen
 Magnesium
 You have identified all the elements
Assignment 1
 What
is the supernova and how does it
differ from the black hole?