Astronomy 101 Flashcards
Define ecliptic
The celestial sphere representing the sun’s apparent path.
Celestial equator
The projection into space of earth’s equator.
Define celestial poles
The point on the celestial sphere directly above either of the earth’s geographical poles, around which the stars and planets appear to rotate. The north celestial pole is currently within one degree of the star Polaris.
Zenith
The point directly above you.
Meridian
The line that passes through both the zenith and the celestial poles.
Zodiac
An imaginary belt in the heavens that includes the apparent paths of most of the planets and is divided into 12 star signs.
Phases of the moon
New moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, waning crescent.
Summer solstice
June 21
Winter solstice
December 21
Equinoxes
September 21st and March 21st
Altitude
How high up in the sky an object lies. Measured from the horizon at 0 and runs from -90 (nadir) to +90 (zenith).
Azimuth
How far around the sky an object lies. Measured from 0 (due North.)
Declination
The “latitude” on the celestial sphere. 0 at the celestial equator. 90 for the North/South Celestial Poles.
Right Ascension
The “longitude” on the celestial sphere. 0 hours at March equinox. Measured as “Hours-Minutes” eastward.
Why does Earth have seasons?
Earth has seasons because it’s axis is tilted. In the equinoxes the sun shines equally on both hemispheres. On solstices it shines on one hemisphere more than the other, because of the tilt.
Geocentric model
Earth is center of the universe. Planets revolve around the earth. Stars are set into a giant unmoving sphere.
-Ptolemy adds epicycles to explain retrograde motion.
Heliocentric model
Aristarchus places sun at the center of the universe.
Planets including Earth revolve around the Sun.
Two main types of eclipse
Solar eclipse, lunar eclipse.
What is the significance of Ptolemy to astronomy?
Ptolemy adds epicycles to the geocentric model.
Moon’s position in solar eclipse
Between earth and sun, with shadow over the earth.
Moon’s position in lunar eclipse.
Earth is between the sun and the moon, with earth’s shadow over the moon.
Why does retrograde motion happen
Because earth is overtaking planets in their orbit.
What were the beliefs of Copernicus?
Believed increasing complexity was not a sign of a good theory.
Made the shift to the heliocentric model of the universe.
Key concepts of Copernicus’ Heliocentric system
- Earth is just one of the planets.
- The daily motion of the sun and stars is the result of earth turning on its axis.
- The sun lies at the center of the solar system.
- All planets orbit in the same direction.
- The orbits are circles and move at a constant speed.
What was Tycho Brahe known for?
His eyesight and accurate naked eye observations of the stars.
What was Tycho Brahe known for?
His eyesight and accurate naked eye observations of the stars.
What event did Tycho observe that helped him disprove the ancient Greeks?
In 1577 he observed a comet that led him to theorize that it and presumably all comets existed far above the atmosphere and deep into the solar system.
Additionally, he observed a supernova breaking the dogma that the heavens were perfect and immutable.
Kepler’s first law of planetary motion
The orbit of each planet around the sun is an ellipse with the Sun at one focus.
Kepler’s second law
As a planet moves around its orbit, it sweeps out equal areas in equal times.
This means a planet travels faster when it is nearer the Sun and slower when it is farther from the Sun.
Kepler’s third law
The period p of an object’s orbit is linearly related to its average orbital distance R.
p squared is directly related to R cubed.
The closer to the sun the faster the orbit.
What was the evidence Galileo used to disprove the Greeks?
Moons of Jupiter did not orbit the Earth.
Ptolemy’s model could not explain the phases of Venus.
Newton’s first law
An object moves at constant velocity unless a net force acts to change its velocity or direction.
Newton’s second law
If a net force is present on an object, there must be a net acceleration of that object.
Newton’s third law
For every force, there is always an equal and opposite reaction force.
What are the types of spectra?
Emission, absorption, continuous.
What is the relationship between energy and frequency in a wave?
The higher the frequency, the more energy the wave carries.
Properties of Continuous Spectra/ what do hotter objects do?
- Hotter objects emit more light at all frequencies
- Hotter objects emit photons with higher average energy.
Emission line spectra
A thin or low density gas cloud emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
Continuous spectra
A cloud of gas can absorb light of specific wavelengths, leaving dark absorption lines.
Absorption spectra- what does the electron do?
Electron absorbs a photon, resulting in an increase of electron energy and an outward transition.
The electromagnetic spectrum
Long to short wavelength
Radio, microwave, infrared, visible, ultraviolet, x-Ray, gama ray.
What is the relationship between wavelength, frequency, and speed of a wave?
Speed is equal to frequency times wavelength.
What is a blackbody?
A blackbody is an object that re radiates exactly as much energy as it absorbs.
What do black body curves do?
Blackbody curves give wavelengths of maximum radiation.
Wien’s law
For black body sources a higher temperature means a shorter wavelength.
