ESRT Astronomy

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Things to know about stars

Star Color and Temperature color is a clue to a star’s
Life cycle

 Apparent Magnitude (luminosity)

• Apparent magnitude is the brightness of a

star when viewed from Earth.

• Three factors control the apparent brightness

of a star as seen from Earth: how big it is,
how hot it is, and how far away it is.

 Absolute Magnitude

• Absolute magnitude is the apparent

brightness of a star if it were viewed from a
distance of 32.6 light-years.

Fill in the Blank

Apparent magnitude is the _________________of a star when viewed from Earth. Doesn't start with an L

Open Ended

How is Absolute magnitude different than apparent magnitude?

 A Hertzsprung–Russell diagram shows

the relationship between the absolute
magnitude and temperature of stars.

Hertzsprung–Russell Diagram

In your ESRT

Hertzsprung–Russell Diagram

The secret lives of stars

Stars age at different rates.

- Massive stars use fuel faster and exist for only
a few million years.

- All stars, regardless of their size, eventually run

out of fuel and collapse due to gravity

Stellar Evolution (baby stars)

 Protostar Stage

• A protostar is a collapsing cloud of gas and

dust destined to become a star—a developing
star not yet hot enough to engage in nuclear
fusion.

• When the core of a protostar has reached

about 10 million K, pressure within is so great
that nuclear fusion of hydrogen begins, and a
star is born.

Nebula, Birthplace of Stars

Main Sequence (all stars)

◆ A main-sequence star is a star that falls

into the main sequence category on the
H–R diagram. This category contains the
majority of stars and runs diagonally from
the upper left to the lower right on the H–R
diagram.

◆ A star spends 90 percent of its life in the

main-sequence stage.

Red Giant (start of the end)

 Red-Giant Stage

• Hydrogen burning migrates outward. The

star’s outer envelope expands.

• The core collapses as helium is converted to

carbon. Eventually all nuclear fuel is used
and gravity squeezes the star.

• Its surface cools and becomes red.

 A red giant is a large, cool star of high
luminosity; it occupies the upper-right
portion of the H–R diagram.

Draw

What is happening to a star that is in the Red giant stage. Be sure to talk about gravity and Fusion pressure

Planetary Nebula

• Cats Eye nebula

Stellar Evolution

 Death of Medium-Mass Stars

• Stars with masses similar to the sun evolve in

essentially the same way as low-mass stars.

• During their collapse from red giants to white

dwarfs, medium-mass stars are thought to
cast off their bloated outer layer, creating an
expanding round cloud of gas called
planetary nebula.

• The end for a medium mass star:
A white dwarf is a star that has exhausted most or
all of its nuclear fuel and has collapsed to a very
small size, believed to be near its final stage of
evolution.

Stars (Large stars)

 A supergiant is a very large, very bright

red giant star.

 A Supernova is a very large explosion

that causes the outer layer of the star to
blow off

 A Neutron star is a very tiny dense star.

 A Black hole Forms when the core of the

massive star is greater than 3x our sun.

Interstellar Matter

• A nova is a star that explosively increases in brightness.

Images of a Nova Taken

Two Months Apart

Stellar Evolution (Death)

 All stars, regardless of their size,

eventually run out of fuel and collapse
due to gravity.

• Stars less than one-half the mass of the sun

never evolve to the red giant stage but
remain in the stable main-sequence stage
until they consume all their hydrogen fuel
and collapse into a white dwarf.

 Death of Low-Mass Stars

Planetary Nebula

Draw

What is happening to a star that is in the last stage of stars. Be sure to talk about gravity and Fusion pressure

Stellar Evolution

• In contrast to sunlike stars, stars that are

over three times the sun’s mass have
relatively short life spans, which end in a
supernova event.

 Death of Massive Stars

• A supernova is an exploding massive star

that increases in brightness many thousands
of times.

• The massive star’s interior condenses and

may produce a hot, dense object that is either
a neutron star or a black hole.

Crab Nebula in the
Constellation Taurus

Stellar Evolution

 White Dwarfs

• A white dwarf is a star that has exhausted

most or all of its nuclear fuel and has
collapsed to a very small size, believed to be
near its final stage of evolution.

The Sun

• The sun begins as a nebula, spends much

of its life as a main-sequence star, and
then becomes a red giant, a planetary
nebula, a white dwarf, and, finally, a black
dwarf.

Stellar Evolution

 Neutron Stars

• A neutron star is a star of extremely high

density composed entirely of neutrons.

• Neutron stars are thought to be remnants of

supernova events.

 Supernovae

• A pulsar is a source that radiates short bursts

or pulses of radio energy in very regular
periods.

• A pulsar found in the Crab Nebula during the

1970s is undoubtedly the remains of the
supernova of 1054.

Stellar Evolution

 Black Holes

• A black hole is a massive star that has

collapsed to such a small volume that its
gravity prevents the escape of everything,
including light.

• Scientists think that as matter is pulled into a

black hole, it should become very hot and
emit a flood of X-rays before being pulled in.

Reorder

Organize the stages of a one mass star from start to finish

• Main sequence

• Red Giant

• White dwarf

• Black Dwarf

1

2

3

4

• 1
• 2
• 3
• 4

Stellar Evolution

Life Cycle of a Sunlike Star

Multiple Choice

The photograph shows a feature of the universe as seen through a telescope. This feature is best identified as

• a galaxy

• a comet

• an asteroid

• a star

Multiple Choice

USE YOUR ESRT! To an observer on Earth, the Sun appears brighter than the star Rigel because the Sun is

• hotter than Rigel

• more luminous than Rigel

• closer than Rigel

• larger than Rigel

Multiple Choice

Which two stars are most similar in luminosity?

• A) Betelgeuse and Barnard's Star

• B) Procyon B and Proxima Centauri

• Alpha Centauri and Sirius

• Polaris and the Sun

Multiple Choice

Which star is cooler and less luminous than the Sun?

• Proxima Centauri

• Pollux

• Rigel

• 40 Eridani

Multiple Choice

During which stage of development does the star have a cool surface temperature and the greatest luminosity?

• protostar

• main sequence

• giant

• white dwarf

Multiple Choice

Energy is produced within a star's core by the process of

• A) insolation

• conduction

• nuclear fusion

• radioactive decay

Multiple Choice

In the graph, which shows changes in the Sun’s magnetic activity and changes in the number of sunspots over a period of approximately 100 years. Sunspots are dark, cooler areas within the Sun’s photosphere that can be seen from Earth.

Which graph best represents the relationship between the number of sunspots and the amount of magnetic activity in the Sun?

Multiple Choice

In the graph, which shows changes in the Sun’s magnetic activity and changes in the number of sunspots over a period of approximately 100 years. Sunspots are dark, cooler areas within the Sun’s photosphere that can be seen from Earth.

The graph indicates that years having the greatest number of sunspots occur

• precisely at the beginning of each decade

• randomly and unpredictably

• in a cyclic pattern, repeating approximately every 6 years

• in a cyclic pattern, repeating approximately every 11 years

Multiple Choice

As the sun ages it will be composed of

• water and ice
• hydrogen

• helium

• Heavier elements like Gold

Multiple Choice

Which statement describes the general relationship between the temperature and the luminosity of main sequence stars?

• As temperature decreases, luminosity increases.

• As temperature decreases, luminosity remains the same.

• As temperature increases, luminosity increases.

• As temperature increases, luminosity remains the same.

Multiple Choice

The star Algol is estimated to have approximately the same luminosity as the star Aldebaran approximately the same temperature as the Rigel.

Algol is best classified as a:

• red giant
• main sequence star
• white dwarf
• neutron star

Multiple Choice

Compared with our Sun, the star Betelgeuse is

• larger hotter and more Luminous

• Smaller cooler and more luminous

• smaller, hotter, and less luminous

• larger, cooler, and more luminous

Multiple Choice

Which star color indicates the hottest star surface temperature?

• yellow
• red
• white

• blue

Multiple Choice

Compared to other stars, the sun is

• among the hottest stars

• very unique

• among the smallest stars

• about average in all respects

Multiple Choice

Which of the following elements is/are represented in the spectrum?

• Hydrogen only

• Helium only

• Hydrogen and Helium

• Calcium only

Multiple Choice

Which element is not represented in the star spectrum below?

• Hydrogen

• Helium

• Calcium

• Magnesium

Multiple Choice

Base your answer to the following question on The reaction represents an energy-producing process

The reaction represents how energy is produced

• in the Sun by fusion

• when water condenses in Earth’s atmosphere

• from the movement of crustal plates

• during nuclear decay

Poll

How confident are you feeling now after doing this about understanding this unit?

• very

• Somewhat

• still missing some things

• I didn't read any of the slides so I don't know anything still