Quiz 2 Flashcards
What is electromagnetic radiation? What are its types?
form of energy known as light. consists of electric and magnetic fields, oscillating perpendicularly to the direction of propagation. examples include: x-rays, uv, infrared, visible, gamma rays, microwaves, radio waves
What is the electromagnetic spectrum? How do we separate it?
collection of all the types of electromagnetic radiation listed above. We seperate it in “bands” or “types”
How do we determine the energy of a wave? What types have the highest energies? The lowest?
The higher the energy of a wave, the smaller its wavelength.
Highest: gamma rays and x rays
Lowest: radio waves
Where do violet and red fall on the visible light spectrum?
shorter wavelengths on the violet side, higher wavelengths on the red side
What EM radiation can pass through our atmosphere?
visible light, radio waves, and a bit of infrared
How do you study visible light, radio waves, and UV IR Gamma X-rays from astrophysical sources?
Visible: ground optical telescopes
Radio waves: ground radios
UV, IR, Gamma, X-rays: space based telescopes
Why do we want to study astrophysical sources in different bands?
-observations at different bands, tell us about different aspects of astrophysical sources
-studying astrophysical sources in the infrared tells us about where the interstellar dust is located
-hotter objects glow at higher energies (gamma rays, x-rays, UV) so studying astrophysical sources in these types tells us about the location of the hottest regions.
Give the most important features of the telescope?
-light gathering power to see fainter objects. to collect more light, increase exposure time or build a telescope with a bigger aperture (collecting area)
-sharpness (resolving power) to see more detailed. to get more sharpness, you need a larger diameter.
Give three types of telescopes.
Radio: big dishes on the ground
Infrared: for example James Webb. need to be in space to eliminate earth’s atmosphere interference
Optical: for example Hubble in space. ground telescopes need to be high to decrease resistance from atmosphere. turbulence reduces sharpness.
Define astronomy.
the scientific study of celestial objects and of phenomena that originate outside Earth’s atmosphere.
What are the 7 celestial objects seen by the ancients (also called wanderers or planetes)?
1- the Sun
2- the Moon
3- Jupiter
4- Venus
5- Saturn
6- Mercury
7- Mars
What are the 5 greek astronomers?
Aristotle
Aristarchus of Samos
Eratosthenes
Hipparchus
Ptolemy
What did Aristotle contribute?
-Aristotle: claimed that earth is a sphere
-observational evidence:
-1)the shadow of the earth on the moon during a lunar eclipse is curved
-2)new stars are visible as one travels north or south
-but Aristotle he also believed in a geocentric (Earth in the middle) model of the universe
What did Aristarchus of Samos contribute?
-Aristarchus of Samos: tried to compare the [distance earth-sun] to the [distance earth-moon] He also tried to compare the size of the sun to the size of the moon. He is also the first person mentioned by name to publish a discussion of the heliocentric model.
-his results: the sun 19 times further away from us than the moon is, so the diameter of the sun must be 19 times larger than diameter of the moon
-true values: the sun is 400 times further away from us than the moon is, and therefore 400 times bigger across
What did Eratosthenes contribute?
1- Measured the tilt of the earth’s rotation axis (tilt value: 23.5 degrees)
2- Measured the radius of the earth
-method for obtaining circumference + radius of earth:
-at noon of specific day in southern egypt (Syene), the sun passes directly overhead
-at alexandria (800 km due north of Syene), at noon on the same day, the sun is about 7.5 degrees away from overhead
-so 7.5 degrees corresponds to 800 km and 360 degrees corresponds to the circumference in km
-from cross multiplying we get: 38400km, so radius is 6111km
-true radius of earth = 6830km (he wasn’t far off at all)
