2.4STUDYING THE SUN

Observing Space

The visible light we see is only a small amount of energy coming from various objects.

By studying other forms of energy, astronomers can learn more about the universe.

Planets do not emit light, but rather reflect it from other stars.

All of the wavelengths of electromagnetic radiation is known as the electromagnetic spectrum.

The Electromagnetic Spectrum

I V

Electromagnetic Radiation

The human eye can only see radiation of wavelengths in the visible light spectrum.

When light passes through a prism, it is refracted (bent), and ROY G. BIV results.

The longer the wavelength, the lower the frequency.

The shorter the wavelength, the higher the frequency.

Telescopes

A telescope is an instrument collecting electromagnetic radiation from the sky. Today, modern telescopes are able

to collect and use both visible and invisible electromagnetic radiation.

Telescopes only collecting visible light are known as optical telescopes.

Telescopes

Two main types of optical telescopes: Refracting: telescopes using a set of lenses to

gather and focus light.▪ Difficult to make large lenses of the required strength.

Reflecting: telescopes using mirrors to gather and focus light.▪ Can be made very large without affecting the quality of

the image.

▪ Hubble Space Telescope is an example.

Refracting Telescope

Reflecting Telescope

Composition of the Sun

Scientists break up the Sun’s light into a spectrum by using a device called a spectrograph.

Each element produces a unique pattern.

75% of the Sun’s mass is Hydrogen (H2) and along with Helium (He), those 2 gases make up 99% of the Sun’s total mass. The Sun’s spectrum shows trace

amounts of other gases as well (remaining 1%).

Types of Spectra

Hydrogen Spectra

Nuclear Fusion

A powerful atomic process is occurring in the Sun, producing energy.

This process is known as nuclear fusion, where the nuclei of small atoms combine to form more-massive nuclei. Releases huge amounts of

energy. Nuclei of Hydrogen (H) atoms

are the primary fuel for fusion in the Sun.

Nuclear Fusion

Nuclear Fusion

Three step process:

1st step 2 Hydrogen (H) nuclei, or protons, collide and fuse.▪ The positive charge of one of the protons is neutralized as a particle called

a positron is emitted. The original 2 protons becomes a proton-neutron pair.

2nd step Another proton combines with the proton-neutron pair to produce a nucleus made of 2 protons and 1 neutron, which is a rare type of Helium (He) known as Helium-3 (3He).

3rd step 2 nuclei made of 2 protons and 1 neutron collide and fuse together.▪ 2 protons are released and the remaining 2 protons and 2 neutrons are

fused together as a final Helium-4 (4He) nucleus results.

Each step of the fusion process releases energy.

Mass Changing Into Energy

One of the final products of fusion of Hydrogen (H) in the Sun is always a Helium (He) nucleus.

In 1905, Albert Einstein proposed a small amount of matter yields a large amount of energy.

This proposal was part of his special Theory of Relativity, which includes the following mass-energy equation: E = mc2

▪ E represents energy▪ m represents mass▪ c represents the speed of light (300,000 km/s)

Equation can be used to calculate the amount of energy produced from a given amount of matter.

Mass Changing Into Energy By using Einstein’s equation, astronomers were able to explain the

huge quantities of energy produced by the Sun (4 million tons of mass converted into energy ever second).

Elements other than Hydrogen (H) can fuse as well.

In stars hotter than the Sun, energy is produced by fusion reactions in the nuclei of other elements such as Carbon (C), Nitrogen (N), and Oxygen (O).

The Core of the Sun

Computer models give us an idea of what the inside of the Sun may look like.

At the center of the Sun is its core. Makes up 25% of the Sun’s total diameter. Extreme temperature of 15,000,000°C (27,000,000°F). Made up of ionized gas since no liquid or solid can exist

at such high temperatures. Where the fusion of Hydrogen (H)

into Helium (He) takes place.

The Radiative Zone of the Sun

Before reaching the Sun’s atmosphere, the energy produced in the core moves through two zones of the Sun’s interior.

The zone surrounding the core is known as the radiative zone. Temperature range: 2,000,000°C

– 7,000,000°C (3,600,000°F – 12,600,000°F).

Energy moves in the form of electromagnetic waves, or radiation.

The Convective Zone of the Sun Surrounding the radiative zone, making up 30%

of the Sun, is the convective zone. Temperature averages about

2,000,000°C (3,600,000°F).

Convection is the transfer of energy, or heat, through moving matter.▪ On Earth, boiling water carries energy upward by

convection.

▪ In the Sun, hot gases carry energy to the surface of the Sun.

The Photosphere of the Sun The innermost layer of the Sun’s atmosphere (where the

interior ends and the atmosphere begins) is called the photosphere. Temperature averages 6000°C (10,800°F). First layer of the Sun visible to us (energy given

off in the form of visible light).

Dark, cool regions in the photosphere are called sunspots. Temperature of these spots is about

3800°C (6800°F).

Caused by changes in the Sun’s magnetic field.

The Chromosphere of the Sun Above the photosphere lies the chromosphere, or the “color sphere”,

of the Sun. Thin layer of gases glowing with reddish light, typical of the color

given off by Hydrogen (H).

Temperature range: 6000°C – 50,000°C (10,800°F – 90,000°F) temperature increase unknown?

Outer Parts of the Sun

The outermost layer of the Sun’s atmosphere is called the corona, or crown.

Huge region of gas with a temperature above 1,000,000°C (1,800,000°F).

Normally not seen from Earth because the sky is too bright during the day.

However, during a total solar eclipse, the moon blocks out the Sun’s photosphere and the corona is visible.

Solar Activity

Astronomers have carefully observed the sunspots in the photosphere of the Sun for hundreds of years. Evidence of the Sun’s rotation.

Noticed the number of sunspots changes over time.

The Sunspot Cycle is an 11 year cycle. Begins when the number of

sunspots is very low but begins to increase until it reaches a peak of 100 or more sunspots then returns to a low number.

Solar Activity

Solar Activity

The solar-activity cycle is caused by the changing magnetic field around the Sun.

Increases and decreases in solar activity, including solar eruptions, events in which the Sun lifts material above the photosphere emitting atomic or subatomic particles.

3 main types of solar eruptions: Prominences Solar Flares Coronal Mass Ejections

Prominences

Changes in the Sun’s magnetic field also create cooler clouds of glowing gases, called prominences. Form huge arches reaching

high above the Sun’s surface.

Follow curved lines of the Sun’s magnetic field.

Can last anywhere from several hours to a few weeks.

Solar Flares

Most violent of all solar disturbances (eruptions) is a sudden outward explosion of electrically charged particles (electrons and protons) known as a solar flare. Most solar flares occur in active regions around sunspots.

During a peak in the 11 year Sunspot Cycle, 5-10 solar flares can happen each day.

Coronal Mass Ejections

Gas particles from the Sun escaping into space from solar eruptions are known as coronal mass ejections. Can play an impact on Earth’s magnetic field and may

damage orbiting satellites.

Coronal Mass Ejections

Coronal Mass Ejections