Earth Science Chapter 24

The functions of a telescope: 

• Telescopes help astronomers in 2 ways: they collect more light, magnify images.

Best ground locations: mountain peaks in dry climates, away from large cities. 

Optical telescopes

• Optical telescopes use lenses or mirrors to gather and focus starlight.

• Light gathering power of a telescope depends on the area of lens or mirror

• Doubling the radius of the lens or mirror increases its light gathering power by four times. 

• Usually kept in buildings with domed roofs. 

• Temperature changes cause the lens to expand or contract. 

• Dome and telescope rotated like earth. 

Refracting telescopes 

• Contain two lenses: objective lenses- located at the front of the tube, gather starlight, very large lens. Eyepiece lens: used to focus and magnify the image. 

• Large refracting telescopes are not built today. The lenses are expensive to make and tend to sag with time. 

Reflecting telescopes: reflecting telescopes use one large objective mirror instead of the lens. 

Other telescopes 

MMT: a multiple mirror telescope, a type of reflector that had multiple mirrors instead of one larger mirror. New telescopes are MMT’s.

Hubble Space Telescope: 1990, mostly visible light

James Webb Telescope: 2021, mostly infrared

Electromagnetic spectrum: 

• The range of wavelengths from radio waves to gamma rays 

• Frequency: the number of wavelengths that pass by a point in one second. 

• Wavelength: distance between crests of a wave. 

• Frequency and wavelength are inversely proportional.

• Higher frequency= shorter wavelength

• All of these travel at the speed of light. 

Radio Astronomy 

• The study of radio waves from space.

• The benefits: can use telescopes during the day, clouds don’t affect it. 

Telescopes for other wavelengths 

• Infrared (IRAS)

• Microwave (COBE)

• X-ray (EXOSAT);(ROSAT)

• Gamma (GRO)

• Problems with infrared earth based telescopes: water vapor absorbs waves, you have to keep the telescope very cold.

• All are non- earth based. 

Spectroscope 

• Separates light into various colors due to the wavelengths refracting at different angles. Long is less. 

• Spectrograph: recording of spectra data.

• Uses: star composition, temperature and pressure; movement of star

Kinds of Spectra

Continuous: unbroken band of colors produced from the following

• Glowing solid

• Glowing liquid

• Compressed gases in stars

Bright line (emission spectra): glowing gas that emits light at a specific wavelength/frequency

Dark Line(absorption spectra): a continuous spectra with dark bands where light is absorbed. Normally exists when gases on a star absorb light from the continuous spectra that they emit. 

Dark line spectra and the solar system

• Dark line spectra from stars of planets show the comparison of the stars outer layers or the planet's atmosphere. 

The Doppler Effect: the compression and expansion of waves caused by the wave moving toward or away from the observer. 

Red shift: when the light gathered from a star has shifted toward the red end of the spectrum due to it moving away from the observer. 

Blue shift: when the light gathered from a star has shifted toward the blue end of the spectrum due to it moving toward the observer.

The Sun:

•  Looking at it improperly, may cause blindness.

• Early Chinese were 1st to notice sunspots.

• Galileo used a telescope to magnify his images.

• Years of looking at the sun caused Galileo to become blind.

• He concluded that the sun rotates based on movements of sunspots.

Solar telescope: projects large images of the sun in a dark underground room to safely view the sun.

Properties of the Sun

• Diameter- 1,380,000 KM

• 110x Earth’s diameter

• Mass- 745x greater than all planets together

• Surface Temp- 5500 degrees C

Source of the Sun’s Energy

• Fusion of Hydrogen into helium in the sun’s core produces massive amounts of energy.

• E = mc2

• Energy = mass x speed of light squared

1. Core: the sun’s nuclear “furnace” where fusion reactions initially combine hydrogen atoms to produce helium, yielding energy in the process. 

2. Radiative Zone: energy moves through a surrounding envelope of gas toward the Sun’s surface.

3. Convection zone: big “bubbles” of hot gas transport energy to the surface

4. Photosphere: the sun’s visible surface. Because of its high temperature, it glows yellow. 

5. Sunspot: a magnetic “storm” of the sun’s surface. 

6. Chromosphere: lower part of the outer atmosphere. Marks layer between photosphere and corona. Red in color. 

7. Corona: The sun’s outer atmosphere, which is heated by the magnetic field to millions of degrees. 

Sun's Atmosphere

3 main regions:

• Photosphere: apparent- bright yellow surface, 400 KM thick, made of millions of individual cells called granules. 

• Chromosphere: lower part of the outer atmosphere, marks layer between photosphere and corona, red in color. 

• Corona: outermost region of the sun, seen during total eclipse as a faint pearly light. 

Solar Prominence- huge arching columns of cooler gas. 

Sunspots: dark spots of cooler regions on the photosphere produced by strong magnetic fields. Occurs in pairs(positive and negative), sunspots move due to the sun's rotation, one rotation for the sun at equator takes 25 days, Near the poles=27 days.

Solar wind: streams of electrically charged particles given off by the corona. Produces auroras.

Solar flares: solar wind bursts, outbursts of light that rise up in areas of sunspot activity. 

C.M.E= Coronal Mass Ejection= massive solar flare.