AstronomyEnvironmental Science

Astronomy is the science that studies the universe.

Astronomy deals with the properties and laws of objects in space.

The universe is made up of galaxies.

There are billions of galaxies in our universe.

Our galaxy is called the Milky Way

Galaxies are made up of Solar Systems centered with stars.

There are eight planets and four smaller bodies (dwarf planets) that orbit the center of our solar system, the sun.

Milky Way Star Map

Moon “Beach” Activities

The Ancient Greeks

Scientists have been researching the sky for almost 3000 years!

Early astronomy was centered in Greece.

The “Golden Age” of Astronomy in Greece: (600 B.C. – 150 A.D.)

Used philosophical arguments and observation.

Greeks developed Geometry and Trigonometry to measure planet size and distances.

Aristotle (384-322 B.C.) believed that the Earth was round because of the curved shadows it formed on the moon. Idea abandoned in Middle Ages.

Early Greeks use philosophy, personal observations and geometry to make astronomical theories.

Famous Greek Astronomers

Aristotle: concluded the earth is round because the shadow the earth casts on the moon is curved.

Aristotle’s Belief (Geo-centric)

Eratosthenes (aka: Big Head): determined the size of the earth

Hipparchus: determined the length of the year & location of many stars

Early Greeks believe in a Geocentric Model

In reality, the solar system is a Heliocentric Model

Aristarchus first proposed the heliocentric model, but no one believed him.

Ptolemy summarized Greek astronomy in a 13-volume work published in 141 A.D.

Ptolemaic System:Ptolemy proposed a motionless earth at the center of our solar system (Geocentric) and people supported this for 13 centuries!

Ptolemy’s Geocentric Model could not explain Retrograde Motion

Retrograde Motion

Retrograde motion is when the planet appears to stop, reverse its direction for a time and then resume the initial, eastward motion.

Retrograde motion cannot be possible, can it? Why? Then HOW does it exist?

Retrograde Motion

“Modern” Astronomy uses natural laws as opposed to philosophical or religious views to determine astronomical theories.

Modern Astronomy!

The Scientists involved in the modern Astronomical theory were from a variety of European countries.

Nicolaus Copernicus (Poland)(1473-1543)

Determined that the earth is a planet, just like other five known planets, and that it rotates.

Also proposed a heliocentric solar system with circular orbits for the planets.

Copernicus’ Conclusions

Tycho Brahe (Denmark) aka Walrus Man(1546-1601)

Became interested in astronomy while viewing astronomer-predicted solar eclipse.

Persuaded King Frederick II to build observatory.

Measured the locations of heavenly bodies for 20 years.

Brahe made observations of Mars and made instruments with which to view the skies.

This angle-measuring device was more precise than any previous methods.

In the last year of his life, Brahe found an able assistant to continue his work: Johannes Kepler. Kepler would outshine his predecessor.

Johannes Kepler (German)

Brahe’ data did not make sense using a geocentric model. But when Kepler placed the sun in the middle of the solar system, and suddenly the data made sense!

Kepler determined the laws of planetary motion.

Kepler’s Laws of Planetary Motion

1. Elliptical Orbits2. Orbits sweep out

equal areas in equal time intervals.

3. Square of period equals cube of distance.

Orbits sweep out equal areas in equal time intervals.

Kepler’s Laws of Planetary Motion

Kepler’s Laws

States that the square of the length of time that it takes a planet to orbit the sun (orbital period) is proportional to the cube of its mean distance to the sun.

Huh?

Kepler’s Third Laws of Motion….

T2 d3

In other words….

€

TATB

⎛ ⎝ ⎜

⎞ ⎠ ⎟2

= dAdB

⎛ ⎝ ⎜

⎞ ⎠ ⎟3

Comparing two planets:

T2 = d3

For the right units….

Distance in astronomical units (1 AU = 150 million km = length of earth’s semi-major axis of its elliptical orbit around the sun)

Period in Earth years.

For example:

Mars has an orbital period of T = 1.88 years. The square of 1.88 is 3.54 (T2). The cube root of 3.54 is 1.52. So the distance from Mars to the sun is 1.52 AU = 228 million km.

The AU stands for astronomical unit is the average distance between the earth and sun is about 150 million km.

Galileo Galilei (Italian) made a telescope and many discoveries.

Jupiter’s four moons; That planets are circular disks; That Venus has phases like our moons; That the surface of our moon is not smooth; The Sun’s sunspots.

Galileo discovered:

Sir Isaac Newton (British) discovered inertia and universal gravitation.

Is a Scientific Law that every body in the universe attracts every other body.

This force of attraction is proportional to their masses and inversely proportional to the square of the distance between their centers of mass.

Universal Gravitation

This force (called gravity) decreases with the square of the distance (inversely proportional).

The larger the mass, the larger the gravitational pull (directly proportional).

The moon has a strong enough pull that it causes tides, but a satellite does not have a large enough pull to have a measurable effect on Earth.

Universal Gravitation

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F =G mAmBd2

Tides are Caused by the Moon