Earth in space Topic 3 in Review Book
I. Celestial observations • All of the objects in our sky appear to be located on a dome (hemisphere) that encircles the earth • This dome is referred to as the • celestial sphere
a. General Terms • The horizon: the imaginary line where the earth appears to meet the celestial sphere
2. The zenith: the point on the celestial sphere directly above an observer… 90º above the horizon
Altitude: a vertical angle… the angular distance above the horizon • Declination: celestial lines of latitude The celestial equator is the reference point + declination = north - declination = south
Azimuth: a horizontal angle: the angular distance measured clockwise from due north. 6. Right Ascension: celestial lines of longitude
Right ascension is labeled in units of time… it is given in hours (h), minutes (m) and seconds (s) and ranges from 0h 0m 0s to 24h 0m 0s
Constellations: groups of stars that appear to form a pattern in the sky • Some stars and constellations are circumpolar… they seem to move in circles around Polaris… when photographed, they create circular star trails
Circumpolar motion occurs because Polaris is directly above our axis of rotation. • The farther north an observer is located, the greater the number of circumpolar stars
Stars/constellations change their position in the sky nightly due to the rotation of the earth and… • seasonally because of the revolution of the earth We’ll talk more about these motions in the next unit…so stay tuned!
d. Some Constellations you should know: i. The Big and Little Dippers: • Seen on the horizon in the fall at the zenith in the spring • The B.D. contains the pointer stars to Polaris
Orion: • We only see it in the winter during “prime time” viewing
Summer Triangle: • We only see it in the summer during “prime time” viewing
B. Origin of the universe • The Big Bang theory: • There is scientific evidence that supports that approximately 14 billion years ago, the universe was a dense concentration of matter that
expanded explosively… At this time: all matter and space was created and moved outward in all directions at the speed of light (300 million m/sec), masses of gas cooled and condensed and…
stellar systems formed. • Evidence of the Big Bang includes: • The uniform age of all of the galaxies
2. Weak electromagnetic radiation from the explosion (cosmic background radiation) has been detected
C. The fate of the universe • In 1929, Edwin Hubble examined the spectra of distant galaxies He compared the spectral lines of far away galaxies to those of nearby stars
Hubble knew that when a light source is moving away from an observer it’s wavelength becomes longer… This results in a shift of its spectrum towards the red end conversely, when a light source moves towards an observer, there is a shift towards the blue end of the spectrum
He found that the nearby stars had spectral lines similar to those expected. But he found that the distant galaxies showed spectral lines shifted to the red end of the spectrum
The shift towards the red end of the spectrum indicated that distant galaxies are moving away from the earth… If the shift had been towards the blue end of the spectrum, the galaxies would be moving towards the earth
Hubble’s law • Galaxies are retreating from us at a speed proportional to their distance from us
Expected spectrum Red shift Blue Shift
The expanding universe theory • proposes that the universe is expanding so that objects (galaxies) move away from one another • The galaxies aren’t expanding…just the spaces between them
D. Classification of stars • Stars are classified based on spectral analysis of their light • This information is organized on a chart called a Hertzsprung-Russell diagram • See ESRT page 15
The H-R diagram is based upon the relationship between the luminosity (brightness) of a star and its temperature • In general…hot stars tend to be blue/white and bright… cool stars tend to be red/yellow and not as bright
When a star varies from this generalization, an inference can be made regarding where it is in its life cycle
E. The Life of A Star • Stars begin as clouds of gas or dust that gets pulled together by a developing force of gravity. As the force of gravity builds, and the star becomes hotter, fusion begins to take place.
Fusion creates an outward force that is in opposition to the inward pull of gravity. These forces, and how balanced they are, determine the life of a star.
Smaller stars last longer than massive stars… Bigger stars are hotter and undergo fusion much faster … therefore, the balance between the forces is upset sooner.
Once fuel begins to diminish, the equilibrium Is disrupted
F. Distances to Stars • The sun is the closest star to earth • It is 150,000,000 km away • This distance is equal to 1 Astronomical Unit (AU)
The next nearest star is Alpha Centauri It is ~ 40 trillion km away This would be ~ 266,666 AU
To make stellar distances more manageable, we convert distances to light years • This is the distance light travels in one year!!!
Light travels 9.5x1012 km/year • Which is 9,500,000,000,000 (9.5 trillion) km/year • Alpha Centauri is 4.35 ly from Earth
It takes the light from the sun 8 minutes and 20 seconds to reach Earth
Another unit of distance is a parsec • Parsec stands for 1 second of parallax Parallax is the apparent shift in the position of one star in relationship to another star This is equal to 3.26 ly