Merrimack College Astronomy 1101

Spring 2017

Ralph P. Pass

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)

The Sun

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

Seismology• We can see undulations in the Sun’s

surface

• These indicate pressure waves in the Sun

• Can be used to understand internal structure

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????

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

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

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)

Prominences Are Not Static!• animation5solar_promine.mov

Effects on Earth

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

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

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

Mercury

Mercury in the Fall

Mercury in the Spring

Mercury

Giovanni Schiaparelli

Mercury

Mercury Interior (best guess)

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

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

Sling Shots

Earth Orbit

Venus Orbit

Mercury Orbit

Messenger Pictures (from orbit)

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)

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

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

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

Venus – Venera 13

Venus - Magellan

Venus - Topography

Measuring Distances• Specifically, how to measure an AU

• Use Parallax!

Advantages of Telescopes

Advantages of Telescopes• Fainter stars

• Better resolution

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

• Do not look directly at the Sun without protection66

Venus Transit

Venus, 6/8/2004 - I

Venus, 6/8/2004 - II

Venus, 6/8/2004 - III

Venus, 6/8/2004 - IV

June 6, 2012 Sunrise San Gimignano

June 2012, San Gimignano

Mercury

Why Venus and Not Mercury?

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

Merrimack College Astronomy 1101

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