nats 1311 - from the cosmos to earth scientific approach to the study of nature copernicus and...

NATS 1311 - From the Cosmos to Earth

Scientific approach to the study of nature

• Copernicus and Galileo introduced observation and experimentation in the 16th century.

• Science is not a set of facts.

• It is a way of conducting a dialogue about our physical surroundings.

• The scientific method consists of careful observation of nature and an open-minded creative search for general ideas that agree with and predict those observations.

• To be scientific, a statement must be capable of being proven wrong.


Scientific approach to the study of nature.

• Observation and experimentation set science apart from other ways of knowing - ways that are not less important - just different

– Philosophy – Reason – Logic

– Art – Appreciation of form – Beauty

• Pseudoscience statements:

– Hypothesis that cannot be tested with reproducible results;

Cold fusion, ufo's, astrology. . .



• Scientific Law: – Statement of observed regularity in nature - attempts to describe the

observations– has a well documented history of successful replication and

extension to new conditions• Scientific Theory:

– Statement of observed regularity in nature - attempts to explain the observations

– General principle offered to explain a set of phenomena or observed facts.

– Not all scientific predictions can be tested directly• Core of earth• Sun—energy• Expansion of the universe

• Require models—creative thought– No ultimate truths—all Provisional

• Ok as long as they are not contradicted



• Model: – Simplified version of reality used to

describe aspects of nature.

– Not synonymous with reality.

– Based on assumptions that may simplify some aspects of nature, or may be incomplete statements about nature

– Useful to make predictions that can be verified by experimentation or observation.


The Scientific Method


Hallmarks of Science

• Modern science seeks explanations for observed phenomena that rely solely on natural causes.

• Science progresses through the creation and testing of models of nature that explain the observations as simply as possible.

• A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations.


The idea that scientists should prefer the simpler of two models that agree equally well with observations - the second hallmark - after medieval scholar William of Occam (1285 - 1349).

For instance, original model of Copernicus (Sun-centered) did not match the data noticeably better than Ptolemy's model (Earth-centered). Thus, a purely data-driven judgment based on the third hallmark might have led scientists to immediately reject the Sun-centered idea. Instead, many scientists found elements of the Copernican model appealing, such as the simplicity of its explanation for apparent retrograde motion. Was kept alive until Kepler found a way to make it work.

Occam’s Razor


The most exciting words in science arenot “Eureka (I found it)” but “Now that’sfunny”.


MOTIONS OF EARTH

1. ROTATION ON ITS AXIS - Day

2. REVOLUTION ABOUT SUN - Year

3. PRECESSION - Wobble of spin axis


Motion Typical Speed

rotation 1,000 km/hr or more around axis, with one rotation taking 1 day

orbit of Sun 100,000 km/hr around Sun, with one orbit taking 1 year

motion within local solar neighborhood

70,000 km/hr relative to nearby stars

rotation of the Milky Way Galaxy

800,000 km/hr around galactic center, with one galactic rotation taking about 230 million years

motion within Local Group 300,000 km/hr toward Andromeda Galaxy

universal expansion more distant galaxies moving away faster, with the most distant moving at speeds close to the speed of light

Motions of Earth


The Earth rotates about its axis axis once per day - one rotation equals one day. The axis goes through the north and south poles and through the center of the Earth. It rotates counterclockwise when looking down on the north pole which means that the sun rises in the east and sets in the west.

Rotation


The Rotation of the Earth From Space

Earth Rotation Movie


Earth’s rotation causes the stars - the celestial sphere - to appear to rotate around the Earth. Viewed from outside, the stars (and the Sun, Moon, and planets) therefore appear to make simple daily circles around us. The red circles represent the apparent daily paths of a few selected stars.


The Celestial Sphere

Envisioned by the ancients, the celestial sphere had Earth at the

center with the stars emblazoned on the sphere. They thought the

stars rose and set because the celestial sphere (the sky) rotated,

carrying the stars from east to west. All stars appear to move

around two points on the celestial sphere, the north and south

celestial poles—projections of earth’s axis of rotation. Earth's

equator projected on the celestial sphere becomes the celestial

equator.


Our lack of depth perception when we look into space creates the illusion that the Earth is surrounded by a celestial sphere. Thus, stars that appear very close to one another in our sky may actually lie at very different distances from Earth.


Constellations

Constellations - groupings of stars named after mythical heroes, gods, and mystical beasts

- made up over at least the last 6000 years - maybe more

- used to identify seasons:

- farmers know that for most crops, you plant in the spring and harvest in the fall.

- in some regions, not much differentiation between the seasons.

- different constellations visible at different times of the year - can use them to tell what month it is. For example, Scorpius is only visible in the northern hemisphere's evening sky in the summer.

- many of the myths associated with the constellations thought to have been invented to help the farmers remember them - made up stories about them


Picture at right shows a start chart of the region around the constellation Orion. Picture at the left is an ornate star chart printed in 1835 - shows the great hunter Orion. He is holding a lion's head instead of his traditional bow or shield. He is stalking Taurus, the Bull in the upper right hand corner. Behind him, his faithful dog, Canis Major, is chasing Lepus, the Hare.


In modern world - constellations redefined so now every star in the sky is in exactly one constellation.

In 1929, the International Astronomical Union (IAU) adopted official constellation boundaries that defined the 88 official constellations that exist today.

ConstellationsWestern culture constellations originated in Mesopotamia over 5000 years ago - added to by Babylonian, Egyptian, and Greek astronomers - current list based charts of Roman astronomer, Claudius Ptolemy (~140 AD)


Star NamesBrightest stars named thousands of years ago - most come from ancient ArabicAstronomers now use Bayer designations for the brighter stars - introduced by Johann Bayer in his star atlas Uranometria in 1603 - consists of a Greek letter followed by the genitive (in Latin) of the name of the constellation in which the star lies:

Aries → Arietis; Taurus → Tauri; Gemini → Geminorum; Virgo → Virginis; Libra → Librae; Pisces → Piscium; Lepus → Leporis.

- brightest star of the constellation given the designation Alpha, the next brightest Beta, and so on.

Flamsteed designations (introduced by John Flamsteed in 1712) - used when no Bayer designation exists - use numbers instead of Greek letters. Numbers were originally assigned in order of increasing right ascension within each constellation - due to the effects of precession they are now slightly out of order in some places.


A model of the celestial sphere shows the patterns of the stars, the borders of the 88 official constellations, the ecliptic, and the celestial equator and poles.


Latitude - lines of latitude parallel to Earth’s equator - labeled north or south relative to equator - from 90º N to 90º S

Longitude - lines of longitude extend from North Pole to South Pole - by international treaty, longitude 0 (the prime meridian) runs through Greenwich, England

Latitude and Longitude

Dallas:latitude = 32.78º Nlongitude = 96.78º W


A circumpolar constellation never rises or sets - they are always visible.Your latitude determines the portion of the celestial sphere visible in your sky.

(a) A Northern Hemisphere sky. (b) A Southern Hemisphere sky.

At what latitude would you see the entire sky?


The Earth's rotation causes stars to trace daily circles around the sky. The north celestial pole lies at the center of the circles. Over the course of a full day, circumpolar stars trace complete circles, and stars that rise in the east and set in the west trace partial circles. Here, the time exposure lasted about 6 hours - we see only about one-quarter of each portion of the full daily path.

Star Trails

The Northern Hemisphere

The Southern Hemisphere


Finding the Celestial Poles

You can always find north using the North Star. Polaris can be found using the big dipper. Draw a line through the two “pointer” stars at the end of the big dipper and follow it upwards from the dipper about four outstretched hand’s width. The big dipper is circumpolar in the US so is always above the horizon. The south celestial pole can be found

using the Southern Cross. There is no “South Star”


The Big and Little Dippers


Motion of the Night Sky Animation


The height in degrees of the north star above the horizon is the same as your latitude.


The angle between the horizon and Polaris is the latitude of the observer.If Dallas is at 33º latitude, where is Polaris in the sky? Where is it at the Equator?


Angular Size

Distances in the sky measured by angular distance:

Minute of arc = 1/60th of a degree

Second of arc = 1/3600th of a degree

Angular diameter - angular distance from one side of an object to the other


Earth travels around the sun (orbits) once per year in the same direction it rotates. It’s orbit is not quite a perfect circle - it is elliptical. The location in the orbit of the minimum and maximum distances from the Sun are called perihelion and aphelion. The plane of the orbit is called the ecliptic.

Revolution


Ecliptic Plane

The Earth’s axis is currently tilted 23.5º to the ecliptic. It varies over time between 22º and 25º due the the gravitational forces from Jupiter and the other planets.

Earth’s Axial Tilt


The axis remains at the same tilt angle - pointed at Polaris - throughout the orbit because of conservation of angular momentum. The ecliptic plane is the plane of the Earth’s orbit. Looking from the Earth, it is the apparent path of the Sun (and planets) in the sky.


The Relationship of the Celestial Equator and the Ecliptic Plane

NATS 1311 - From the Cosmos to Earth The Zodiac

The Sun appears to move steadily eastward along the ecliptic, through the constellations of the zodiac. As Earth orbits the Sun, we see the Sun against the background of different zodiac constellations at different times of year. For example, on August 21 the Sun appears to be in the constellation Leo. Defines astral calendar.


Sun’s Path Through the Zodiac


Celestial Sphere

The apparent Sphere of the sky

Celestial Poles

The points about which the celestial sphere appears to rotate

Celestial Equator

Projection of the Earth’s equator on the celestial sphere

Ecliptic Apparent annual path of the sun on the celestial sphere

nats 1311 - from the cosmos to earth scientific approach to the study of nature copernicus and...

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