The Hertzsprung-Russell Diagram
Flattening of a solar nebula
1. As the nebula collapses, the wind created causes clumps of gas collide & merge. 2. Swirling winds cause the nebula to assume the shape of a disk.
The H-R diagram
1. plots the luminosity (brightness) or absolute magnitude of stars against their surface temperatures. 2. Most stars fall into distinct groups in the H-R diagram, because the groups represent stages in the life cycles of the stars.
Giant stars
1.Above the main-sequence stars. 2.They are more luminous and have diameters from 10-100 times greater than our sun.
main-sequence stars
1.The stars in this band. 2.Main-sequence stars vary in surface temperature and absolute magnitudes. 3.However, ALL main-sequence stars are actively fusing hydrogen into helium.
main sequence
About 90% of all stars seem to fit in a band that runs from the upper left of the diagram to the lower right.
first-magnitude stars
Classified as some of the brightest stars in the sky.
How Stars Form
Collapsing gas and dust clouds. (This picture is called the "Pillars of Creation" because new stars are being born in different parts of the nebula as the gas clouds collapse and begin spinning.)
Life cycle of our sun
Our sun is a small to average star. No supernova in the future. It will end as a white dwarf that eventually fades away.
What is important of a star?
Remember, the mass and the temperature of the star are important!
one solar mass
Stellar masses are expressed as multiples of the mass of our sun
sixth-magnitude stars
The faintest stars that can be seen with our unaided eye.
white dwarfs
These are stars that are near the end of their lives. RED GIANT STARS THAT LOSES THEIR OUTER ATMOSHERE and are now only a glowing stellar core.
Life Cycle of a Star
This diagram follows the life of both large and average stars. The life path of a star is dependent on the MASS of the star. Low mass stars take the top path. High mass stars take the bottom path.
Ejnar Hertzsprung Denmark & Henry Russell (USA)
Two astronomers discovered a relationship between the absolute magnitude (real brightness) of a star and its surface temperature. They plotted the data on a graph.
What can we NOT observe?
We cannot observe a star's mass directly.
The hottest stars (such as Sirius) have
a bluish white color (above 9500° C).
Protostar
a developing star. Not yet a star. No nuclear fusion happening yet. (The temperature continues to increase as the gas cloud compresses and spins faster and faster. Once the temperature reaches 10 Million Degrees Kelvin (18 Million Degrees Fahrenheit) then nuclear fusion begins and the star is born. )
distance from Earth no longer becomes
a factor in how bright a star is. Remember, very bright stars that are very far from Earth may appear to be very faint to us.
Cooler surface temperatures (below 3900° C) results in
a red coloring (for example, Betelgeuse).
Super giants
are giant stars that have diameters more than 100 times greater than our sun. These giant stars (but relatively cool) are very luminous.
Apparent Magnitude
is a measure of how bright a star appears to be to an observer on Earth. It is how bright a star appears to be from earth due to how close or far away it is.
Absolute magnitude
is a measure of how bright a star would be if all stars were at the same distance (ten parsecs) from Earth. It is how much light is actually given off by a star.
Hotter temperatures change the color to
orange, then yellow (our sun, at about 5500° C), and then white.
Some stars are so bright
that they have a negative apparent magnitude.
The lower the apparent magnitude number
the brighter the star is.
We can only calculate...
the star's mass based on other observations.
The larger the mass,
the stronger the gravitational effect on the bodies around it.
Stars vary greatly in...
their masses, size, and densities.
Stars temp....
vary in temperature. The range of colors a star emits depends on its surface temperature. Analyzing the light emitted by a star helps us to determine the stars temperature.
