The Sun through the Eyes of soho: New Insight into our Star, and its Impact on the Earth’s Environment The Sun

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The Sun through the Eyes of SOHO: New Insight into our Star, and its Impact on the Earth’s Environment

The Sun

  • The Sun is located in a spiral arm of our Galaxy, in the so-called Orionis arm, some 30,000 light-years from the center.

  • The Sun orbits the center of the Milky Way in about 225 million years. Thus, the solar system has a velocity of 230 km/s (or 830 000 km/h)

  • Our galaxy consists of about 100 billion other stars and there are about 100 billion other galaxies

  • The Sun has inspired mythology in many cultures including the ancient Egyptians, the Aztecs, the Native Americans, and the Chinese.

  • The Sun is 333,400 times more massive than the Earth and contains 99.86% of the mass if the entire solar system

  • It consist of 78% Hydrogen, 20% Helium and 2% of other elements

  • Total energy radiated: 100 billion tons of TNT per second

The Sun’s Structure

  • Core

    • Where the energy is created.
    • Nuclear reactions burn every second about 700 million tons of hydrogen into helium.
  • Radiation Zone

    • Where energy is transported by radiation.
    • Although the photons travel at the speed of light, they bounce so many times through the dense material that they use about a million years to escape the Sun.
  • Convection Zone

    • Energy transported by convection (just like boiling soup) where heat is transported to the photosphere.


  • Dark areas (umbra, penumbra)

  • Strong magnetic fields

    • Inhibit energy transport from solar interior
    • Cooler areas, and therefore darker

The Sun’s Magnetic Field

  • The Sun is strongly affected by magnetic forces.

  • The red arrows show open magnetic field lines emerging from the poles.

  • The gray arrows represent solar wind particles which carry field lines with it.

  • The bright active regions have closed magnetic field lines (orange).

Solar Activity 1992-1999

The Solar Corona

  • The corona is the area just above the surface. While the surface is about 5,000o Celsius, the temperature in the corona reaches about 2 million degrees Celsius. What causes this rapid increase in tempera-ture is still one of the big mysteries in solar physics.

What is the Solar Wind?

  • A constant stream of particles flows from the Sun’s corona, with a temperature of about a million degrees and with a velocity of about 450 km/s. The solar wind reaches out beyond Pluto's orbit (about 5900 million kilometers). The drawing shows how it pushes on and shapes the Earth’s magnetosphere (the dotted line).

The SOHO Mission

  • Joint program between the European Space Agency (ESA) and NASA.

    • An industry team led by Matra Marconi Space built SOHO in Europe. It’s instruments were provided by nine European and three U.S. Principle Investigators
    • ESA: responsible for SOHO’s procurement, integration, and testing
    • NASA: provided launch and mission operations (at Goddard Space Flight Center)

Science Objectives

  • Solar Interior: What are its structure and dynamics?

  • Corona: Why does it exist and how is it heated?

  • Solar Wind: Where is it accelerated and how?

SOHO Operations

  • Unique Operations Mode

    • “Live” display of data on scientists’ workstations
    • Real-time commanding by scientists, directly from their workstations
  • Emphasis on Coordinated Observations

    • Internally - daily planning meetings at EOF
    • Externally - campaigns and collaborations; coordination and data exchange over Internet


  • The entire Sun vibrates from a complex pattern of acoustic waves

  • The Sun's acoustic waves bounce from one side of the Sun to the other, causing the Sun's surface to oscillate up and down

  • The sound waves are influenced by conditions inside the Sun

  • By observing these oscillations on the surface we can learn about the structure of the solar interior

Solar Interior Structure Rotation

Surface Dynamics - Oscillations

Time-Distance Helioseismology

  • New technique which is primarily developing with SOHO/MDI data

  • First ever images of flows in the convection zone of a star

  • First images of the subsurface structure of sunspots

    • Can give us the first insight into how sunspots are formed

SOHO sees through the Sun

The Pulse of the Sun’s Dynamo

The Beauty of the Sun EIT He II 304 Å 27 July 1999

3 Weeks of EIT observations

… loops, loops, loops ...

TRACE: “the new kid on the block”

EUV Spectroscopy with SOHO

Loop Dynamics / Active Region Flows

Heating of the Corona The Magnetic Carpet

The Temperature of the Corona

Acceleration of the Fast Solar Wind

Source Regions of the High Speed Solar Wind

  • SUMER spectroscopic observations in a coronal hole in Ne VIII 770Å (650 000 K)

  • Shows outflows (blue shifts) in coronal hole as compared to red shifts in quiet Sun

  • Largest outflows occur along the boundaries and the intersections of the chromospheric network (superimposed dark lanes)

    • “solar wind breaking through network like grass around the edges of paving stones in a patio”

Elemental and Isotopic Composition of the Solar Wind

Eruptive Prominences

Eruptive Prominences

The many faces of CME’s

Coronal “Moreton” Waves

  • Speeds: 200 - 600 km/s

  • Deflected by AR

  • Stop at CH boundaries

  • Usually associated with CMEs

  • Fast-mode Alfvén shock (cf. Uchida 1968, 1973)

Comets observed with SOHO/LASCO (over 290 comets discovered so far!)

Comet Discoveries

  • As of 5 Feb 2001, SOHO discovered a total of 293 comets (LASCO: 292, SWAN: 1)

  • Almost 25% of all comets dicoveries since 1760 come from SOHO.

  • More than 85% of the comet discoveries during the past two years come from the SOHO and LINEAR programs.

  • Studies on dust-production of sungrazers:

    • tails straight and narrow
    • no evidence for Lorentz force on charged dust
    • tails include a major population of sub-micron-sized dielectric grains (most probably silicates)

UV Spectroscopy of a Sungrazing Comet Comet C/2001 C2 (SOHO-294)

  • Discovered in LASCO real-time images on Internet by two amateur astronomers

    • Sebastian Hoenig, Germany
    • Xing Ming Zhou, China)
  • Outgassing rate  100 kg/s

  • Size of comet nucleus  10 m

  • Densities:

    • 10,000 particles/cm3 at 4.82 R
    • 86,000 particles/cm3 at 3.32 R

Shadow of a Comet

Looking at the Far Side of the Sun

SOHO Captures Planet Gathering

From Solar Min towards Solar Max

The Extended Corona

Solar Irradiance Measurements - The Sun as a Star

  • VIRGO - Total solar irradiance

  • CDS: EUV 307-380 Å and 515-632 Å spectral irradiance and 69 full disk images taken each month

  • SEM (CELIAS): EUV disk integrated flux from 1-500Å and in 260-340 Å (He II 304 Å)

SOHO and CMEs: To the Max?

The 14 July 2000 Event

The 14 July 2000 Event

The 14 July 2000 Event

The 14 July 2000 Event

What is Space Weather?

Aurora Borealis

Effects from Solar Storms

Navigation systems (GPS, LORAN C)

Satellite Failures due to Space Weather Effects

Geomagnetic Induced Currents

Damage to Transformers

High Energy Particles Hazards to Humans

Our society are much more dependant on technology today compared to in 1989

  • Our society are much more dependant on technology today compared to in 1989

  • The most rapidly growing sector of the communication market is satellite based

    • Broadcast TV/Radio,
    • Long-distance telephone service, Cell phones, Pagers
    • Internet, finance transactions
  • Change in technology

    • more sensitive payloads
    • high performance components
    • lightweight and low cost
  • Humans in Space

    • More and longer manned missions
  • Space Weather warning will be very

  • important for our society in the future.

Solar Cycles and Climate Variations

The Sun and Global Warming

Variations in the Solar Magnetic Flux

Cosmic Rays and Clouds

Why does the Sun Vary?

  • Why does the Sun Vary?

    • solar dynamo
    • atmosphere
    • heliosphere
  • How does solar variability affect life and society?

    • magnetosphere response
    • “space weather forecast”
  • How do the planet respond to solar Variations?

    • climate changes

GSFC: June 25 1998 (07:12 UT)

The Drama of the Summer of 1998

We did it!

New features on the SOHO Web-pages

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