Astronomy Chapter 10

Sun importance

The Sun is the source of light and heat on Earth and is essential for human existence

Sun as a typical star

The Sun has properties typical of many stars

Purpose of studying the Sun

Studying the Sun helps us understand other stars

Closest star

The Sun is the closest star to Earth

Quiet Sun definition

Solar phenomena that appear regularly and consistently

Active Sun definition

Solar phenomena that vary over time and are not uniform

Solar eclipse importance

Total solar eclipses allow observation of the Sun’s outer atmosphere

2017 solar eclipse significance

Provided coordinated observations from ground and space across the U.S.

Solar observation methods

Telescopes, spacecraft, and eclipse observations

Solar corona observation

The corona is best seen during total solar eclipses

Diamond-ring effect

Bright flash of light seen just before and after totality during an eclipse

Coronal streamers

Long, thin structures extending outward from the corona

Solar corona appearance

Pearly white outer layer seen during eclipses

Photosphere definition

The visible “surface” of the Sun

Meaning of photosphere name

Derived from Greek “photos” meaning light

Photosphere role

Layer from which most visible light is emitted

Photosphere temperature

Approximately 5800 K

Sun color reality

The Sun is actually white

Why Sun appears yellow

Atmospheric scattering of blue light makes it appear yellow

Why Sun appears red/orange

When near horizon, more scattering removes blue/green light

Solar filter effect

Filters used in images enhance yellow/orange appearance

Sun size compared to Earth

The Sun is about 110 Earth diameters across

Sun volume comparison

Over 1 million Earths could fit inside the Sun

Measuring Sun size

Done using angular diameter and distance

Transit method

Measuring planetary transits (like Venus) to determine distances

Rarity of Venus transits

Occur rarely; last occurred 2004 and 2012

Next Venus transit

Will occur in 2117

Sun composition hydrogen

About 92% hydrogen

Sun composition helium

Just under 8% helium

Sun composition other elements

About 0.2% other elements

How Sun composition is measured

Using spectroscopy (studying spectra)

Solar seismology definition

Study of oscillations to determine internal structure and composition

Helium abundance measurement

Best measured using solar seismology

Sun classification range

Stars can be hotter/cooler and brighter/fainter than the Sun

Most common stars

Most stars are cooler and fainter than the Sun

Radiation peak of Sun

Occurs in visible spectrum

Reason humans see visible light

Eyes evolved to match peak solar radiation

Hypothetical x-ray vision

If Sun emitted mostly x-rays, humans might see in x-rays

Solar interior location

Beneath the photosphere

Solar core definition

Central region where energy is generated

Solar core size

About 10% of the Sun’s diameter

Solar core temperature

About 15,000,000 K

Solar core function

Location of nuclear fusion

Energy source of Sun

Nuclear fusion in the core

Radiative zone definition

Region where energy moves outward by radiation

Convective zone definition

Region where energy moves outward by convection

Convection definition

Heat transfer through rising and falling material

Granulation pattern

Visible pattern caused by convection on the photosphere

Sunspots definition

Darker, cooler regions on the photosphere

Sunspot cause

Strong magnetic fields inhibit convection

Sunspot temperature

Cooler than surrounding areas

Sunspot appearance

Dark spots on the Sun’s surface

Active regions

Areas with many sunspots and magnetic activity

Magnetic field of Sun

Measured and observed through solar imaging

Sunspot cycle

Approximately 11-year cycle of solar activity

Solar maximum

Time of highest sunspot activity

Solar minimum

Time of lowest sunspot activity

Starspots on other stars

Observed on other stars similar to sunspots

Chromosphere definition

Layer above the photosphere

Chromosphere thickness

About 1% of the Sun’s radius

Chromosphere temperature range

About 7000 K to 15,000 K

Chromosphere temperature comparison

Hotter than the photosphere

Chromosphere color

Pink glow seen during eclipses

Spicules definition

Jets of rising and falling gas in the chromosphere

Spicule behavior

Rapid upward and downward motion of plasma

Flash spectrum definition

Spectrum seen briefly during solar eclipses

Corona definition

Outermost layer of the Sun’s atmosphere

Corona temperature

A few million Kelvin

Corona temperature paradox

Corona is much hotter than lower layers

Corona visibility

Visible during total solar eclipses as a halo

Coronal holes definition

Dark regions in the corona with lower density

Solar flares definition

Sudden releases of energy from the Sun’s surface

Prominence definition

Loops of glowing gas extending from the Sun

Prominence structure

Shaped by magnetic fields

Solar activity definition

Phenomena such as flares, sunspots, and prominences

Solar magnetic field importance

Drives solar activity and structures

Solar wind definition

Stream of charged particles from the Sun

Corona source of solar wind

The corona releases solar wind into space

Impact of solar wind

Affects planetary atmospheres and space weather

Space weather definition

Conditions caused by solar activity affecting Earth

Auroras cause

Interaction of solar wind with Earth’s magnetic field

Solar atmosphere layers

Photosphere, chromosphere, corona

Photosphere position

Lowest visible layer of the atmosphere

Chromosphere position

Middle layer above photosphere

Corona position

Outermost atmospheric layer

Solar structure diagram elements

Core, radiative zone, convection zone, atmosphere

Subsurface flows definition

Movement of plasma beneath the surface

Solar limb definition

Edge of the Sun as seen from Earth

White-light image definition

Image showing visible light from the Sun

Magnetic image definition

Image showing magnetic field structure

Difference in images

Magnetic images highlight active regions not visible in white light

Sunspot visibility during eclipse

Better seen at the limb during totality

Solar brightness reduction

Imaging requires reducing brightness by ~100,000 times

Importance of eclipses

Only time full corona is visible from Earth

Spacecraft solar observations

Provide high-resolution images outside Earth’s atmosphere

Solar spectrum definition

Distribution of wavelengths emitted by the Sun

Spectral lines definition

Dark or bright lines indicating element presence

Element identification

Spectral lines reveal chemical composition

Solar radiation definition

Energy emitted by the Sun across electromagnetic spectrum

Visible spectrum importance

Region where most solar energy is emitted