Final Astronomy Flashcards
From where on Earth could you observe all of the stars during the course of a year?
Equator line
What were four of Galileo’s discoveries that were important to astronomy?
- Venus phases
- 4 moons around Jupiter
- More stars then the human can see
- Craters and mountains on the moon
How many degrees does the Sun move per day relative to the fixed stars?
The sun moves 1 degree a day
What two factors made it difficult, at first, for astronomers to choose between the Copernican heliocentric model and the Ptolemaic geocentric model?
Lack of observational data and religious beliefs
- Which has more mass: an armful of feathers or an armful of lead?
- Which has more volume: a kilogram of feathers or a kilogram of lead?
- Which has higher density: a kilogram of feathers or a kilogram of lead?
- Lead
- Feathers
- Lead
According to Kepler’s second law, where in a planet’s orbit would it be moving fastest? Where would it be moving slowest?
It would be moving fastest at perhelion and slowest at aphelion
Explain how a rocket can propel itself using Newton’s third law.
When a rocket engine burns fuel and expels hot exhaust gases backwards (the action), the force of those gases pushing against the rocket nozzle creates an equal and opposite force propelling the rocket forward (the reaction).
What is the average distance from the Sun (in astronomical units) of an asteroid with an orbital period of 8 years?
a^3=p^2
a^3=8^2
a= 4AU
Make a list of each main phase of the Moon, describing roughly when the Moon rises and sets for each phase. During which phase can you see the Moon in the middle of the morning? In the middle of the afternoon?
New Moon: rises at sunrise, sets at sunset
1st Quarter: rises at noon, sets at midnight (can see middle of afternoon)
Full Moon: rises at sunset, sets at sunrise
3rd Quarter: rises at midnight, sets at noon (can see middle of morning)
What is the right ascension and declination of the Sun at noon on the winter solstice in the Northern Hemisphere?
d: -23.5 degrees and a: 18 hours
Explain why some solar eclipses are total and some are annular.
Total solar eclipses happen when the full moon is perigee, meaning it can fully block the sun.
Annular solar eclipses happen when the full moon is apogee, meaning it can’t fully block the sun.
If Sirius rises at 8:00 p.m. tonight, at what time will it rise tomorrow night, to the nearest minute? Explain.
7:56pm, the sidereal day is 4 minutes lower then a solar day
Explain why we have to observe stars and other astronomical objects from above Earth’s atmosphere in order to fully learn about their properties.
The atmosphere blocks many waves, meaning we can’t get a full study on stars and other astronomical objects
Explain why astronomers use the term “blue shifted” for objects moving toward us and “redshifted” for objects moving away from us.
When objects are shifting towards you, the waves get smaller and shift to the bluer spectrum
And for objects shifting away, the waves get longer, and shift to the redder side of the spectrum
What is the frequency of a red laser beam, with a wavelength of 670 nm, which your astronomy instructor might use to point to slides during a lecture on galaxies?
c=λf –> f=c/λ
nm = 10^-9
speed of light: 3 x 10^8
3 x 10^8 / 670 x 10^-9
= 4.5 x 10^14 hz
What is the temperature of a star whose maximum light is emitted at a wavelength of 290 nm?
λmax= 2.9 x 10^6 / T
T= 2.9 x 10^6 / λmax
2.9 x 10^6 / 290 = 10,000 K
When astronomers discuss the apertures of their telescopes, they say bigger is better. Explain why.
Aperture can increase resolution and light gathering
What is meant by “reflecting” and “refracting” telescopes?
A “reflecting telescope” uses mirrors to focus light and create an image, while a “refracting telescope” uses lenses to bend light and focus it
Describe the techniques radio astronomers use to obtain a resolution comparable to what astronomers working with visible light can achieve.
They use a technique called interferometry, where 2 or more telescopes are linked together to increase resolution
Venus rotates backward and Uranus and Pluto spin about an axis tipped nearly on its side. Based on what you learned about the motion of small bodies in the solar system and the surfaces of the planets, what might be the cause of these strange rotations?
Something collided or impacted them, changing it’s angle
What is the difference between a meteor and a meteorite?
Meteor: In the sky
Meteorite: On the ground
Meteoroid: In space
Why are there so many craters on the Moon and so few on Earth?
The Earth’s atmosphere burns or breaks up meteors, it’s weather also causes craters overtime to disappear.
A radioactive nucleus has a half-life of 5×10^ 8years. Assuming that a sample of rock (say, in an asteroid) solidified right after the solar system formed, approximately what fraction of the radioactive element should be left in the rock today?
Fraction = (1/2) ^ t/t(half life)
1/2^(4.5 x 10^9/ 5 x 10^8)
= 0.002
Solar system formed: 4.5 x 10^9 years ago
In broad daylight, the size of your pupil is typically 3 mm. In dark situations, it expands to about 7 mm. How much more light can it gather?
pi x r^2
pi(7/2)^2/ pi(3/2)^2
= 7/3^2
= 5.4 times brighter