Merrimack College Astronomy 1101

Copyright 2017 © Ralph P. PassFebruary 23, 2017 1

Merrimack College Astronomy 1101

Spring 2017

Ralph P. Pass

Copyright 2017 © Ralph P. PassFebruary 23, 2017

Solar System• Four groups of objects • Star (object making its own energy using

atomic fusion)

• Rocky or Terrestrial planets

• Giant Planets (Giants, two gaseous, two ice)

• Debris (everything else)

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The Sun

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The Sun• Is a star (nearest star)

• Star means it creates its own energy by fusing matter

• The sun is ten times the diameter of Jupiter (which is ten times the diameter of the Earth)

• Gravity creates intense pressure and temperature at the center

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Seismology• We can see undulations in the Sun’s

surface

• These indicate pressure waves in the Sun

• Can be used to understand internal structure

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Sun’s Power Source• Ancients thought it was wood

• 19th century scientists thought it was coal • And concluded it would burn for 20,000,000

years (assuming you knew where to get the oxygen)

• How is this consistent with the Earth being 4.5 billion years old????

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Sun’s Power Source• High Pressure means High Temperature means High Speeds

for atoms • Initially this was the result of gravitation • High speed and pressure allow for atoms to ‘fuse’ • This is the basis for a Hydrogen Bomb

• Four hydrogen atoms fuse in a three step process to form helium (the next element up)

• There is a small decrease in mass when this happens • And Einstein found that • E = mc

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• Small mass yields large energy (e.g., a paperclip converted to energy is 20,000 tons of TNT, equivalent to the Hiroshima bomb)

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Solar Activity• Obvious features are sunspots • ‘Dark’ (= cooler) regions on the sun

• Caused by the Sun’s Magnetic Field

• The number of sunspots vary in an 11 year cycle

• Sun’s magnetic field flips every 11 years (so real cycle is 22 years for the Solar Cycle)

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Prominences Are Not Static!• animation5solar_promine.mov

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Effects on Earth

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Question to think about• Sunspots are cooler than the surface of the

sun

• So, when would the Earth get more energy (heat)? During sunspot maximum or sunspot minimum?

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Modern Problems• Satellites are sensitive to radiation

• CME’s have caused satellite failures, power grid failures

• Some CME’s are so powerful that had astronauts been outside the protective magnetic field of the Earth (e.g., on the Moon), they would have died

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Mercury

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Mercury in the Fall

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Mercury in the Spring

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Mercury

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Giovanni Schiaparelli

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Mercury

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Mercury Interior (best guess)

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Mercury - Facts• No atmosphere

• Very dense (to be formed only heavy matter had a chance to solidify) • Mercury is 5.4

• Venus is 5.2

• There is water ice in the craters at the poles

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Mercury - Facts• To get to Mercury, Mariner 10 had to first

fly by Venus • We did not have sufficient energy to go directly

• This maneuver is called a gravity assist or sling shot

• Shows the difference between speed and velocity • Speed is distance per time • Velocity is speed in a particular direction

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Sling Shots

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Earth Orbit

Venus Orbit

Mercury Orbit


Messenger Pictures (from orbit)

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Venus

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Venus• Twin in size to the Earth

• Appears virtually featureless in a telescope

• Mimics the phases of the moon

• Brightest object in the sky after the Sun and the Moon

• Magnitude -4.4 (three magnitudes or 15.8 times brighter than Sirius, the brightest star)

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Venus• Observers thought they could see subtle features

and concluded a rotation rate of 6 days • They were seeing cloud variations

• Using blue filters

• Object of the first successful planetary exploration by human sent spacecraft • Mariner 2, 1962

• Determined that the surface temperature was 800 degrees and cloud tops were cold

• First Planet detected by Radar, Arecibo, 1964

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Venus• US has studied the planet with orbiting

satellites • Radar Altimeters

• Radar Imagers

• So we have a ‘picture’ of the surface, mountains, valleys, etc

• The USSR has landed spacecraft on the surface where they survive for about 40 minutes

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Venus• Carbon Dioxide Atmosphere with an abundance

of Sulfuric Acid

• High Pressure, dense atmosphere (about 100 times more ‘air’ than Earth’s atmosphere)

• Greenhouse run amok

• In the 1960s it was thought to have a rotation locked with its orbit about the Sun (224 days to orbit the Sun)

• Later data showed the rotation is retrograde once every 243 days

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Venus – Venera 13

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Venus - Magellan

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Venus - Topography

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Measuring Distances• Specifically, how to measure an AU

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Measuring Distances• Specifically, how to measure an AU

• Use Parallax!

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Advantages of Telescopes

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Advantages of Telescopes• Fainter stars

• Better resolution

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Venus Transit• June 8, 2004 at Sunrise and June 5/6, 2012 • Transits happen in pairs • Two transits 8 years apart

• Pairs of transits are separated by 122 years • So nobody alive had seen a transit by Venus prior to June 8, 2004

• Used to assign a measurable distance to the Sun (e.g., what is an AU in miles) • First done in the 1639 Transit by Jeremiah Horrocks • Kepler had ‘measured’ solar parallax and concluded 1 AU =

10,000,000 miles. • Horrock used a Venus Transit to conclude 1 AU = 59,500,000

miles

• Do not look directly at the Sun without protection66


Venus Transit

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Venus, 6/8/2004 - I

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Venus, 6/8/2004 - II

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Venus, 6/8/2004 - III

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Venus, 6/8/2004 - IV

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June 6, 2012 Sunrise San Gimignano

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June 2012, San Gimignano

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Mercury

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Why Venus and Not Mercury?

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Why Venus and Not Mercury?• Bigger Parallax Shift so better accuracy

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Merrimack College Astronomy 1101

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