 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

 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.

 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.

 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.

 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 (H 2 ) 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%).

 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.

 Three step process:  1 st 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.  2 nd 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 ( 3 He).  3 rd 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 ( 4 He) nucleus results.  Each step of the fusion process releases 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 = mc 2 ▪ 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.

 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 every 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).

 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.

 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.

 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 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.

 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?

 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.

 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.

 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

 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.

 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.

 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.