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
Why do sunspots look dark?
The sunspot’s area of gas has a lower temperature compared to surrounding gas.
Which aspects of the Sun’s activity cycle have a period of about 11 years?
Which vary during intervals of about 22 years?
The sunspot cycle peaks every 11 years.
The solar magnetic cycle is every 22 years and the polarity of the sunspots reverses.
What is the Zeeman effect and what does it tell us about the Sun?
The magnetic field of the Sun causes spectral lines to split, which tells us about the strength of the magnetic field of the Sun.
How can the prominences, which are so big and ‘float’ in the corona, stay gravitationally attached to the Sun while flares can escape?
The flares are going faster then escape velocity and the Sun’s has a lot of gravity.
Explain how we know that the Sun’s energy is not supplied either by chemical burning, as in fires here on Earth, or by gravitational contraction (shrinking).
Chemical burning isn’t possible without oxygen, which the Sun barely has. The sun also is not shrinking so gravitational contraction isn’t a contributor. These would also be too small of sources to sustain the Sun’s energy.
What is the ultimate source of energy that makes the Sun shine?
Nuclear Fusion
Describe in your own words what is meant by the statement that the Sun is in hydrostatic equilibrium.
Fusion expands the Sun and gravity tries to collapse it, making an equilibrium
Describe the two main ways that energy travels through the Sun.
Radiation and Convection
What two factors determine how bright a star appears to be in the sky?
Luminosity of a star and it’s distance
Explain why color is a measure of a star’s temperature.
The spectrum of colors, from red to blue correlate with the stars temperature. The more blue side of spectrum, the hotter, and the more red side of spectrum, the cooler.
The star Antares has an apparent magnitude of 1.0, whereas the star Procyon has an apparent magnitude of 0.4. Which star appears brighter in the sky?
Procyon, because the smaller the magnitude the more bright.
Star A and Star B have different apparent brightness’s but identical luminosities. If Star A is 20 light-years away from Earth and Star B is 40 light-years away from Earth, which star appears brighter and by what factor?
Star A is closer, and will be brighter by a factor of 1/4, so 4x times brighter
2x times away from Star A, inverse square law: 1/d ^2
1/2^2= 1/4
Name and describe the three types of binary systems.
𝑽𝒊𝒔𝒖𝒂𝒍 𝒃𝒊𝒏𝒂𝒓𝒚: two stars can be resolved by a telescope
𝑺𝒑𝒆𝒄𝒕𝒓𝒐𝒑𝒔𝒄𝒐𝒑𝒊𝒄: spectral lines are doppler shifted showing orbital motion
𝑬𝒄𝒍𝒊𝒑𝒕𝒊𝒏𝒈 𝒃𝒊𝒏𝒂𝒓𝒚: we observe a light curve as stars ecliptic one another
Describe how the mass, luminosity, surface temperature, and radius of main-sequence stars change in value going from the “bottom” to the “top” of the main sequence.
Radius, temperature, and luminosity all increase in top main sequence stars.
There are fewer eclipsing binaries than spectroscopic binaries. Explain why.
Our perspective on Earth can change whether or not they are eclipsing based on their angle.
If two stars are in a binary system with a combined mass of 5.5 solar masses and an orbital period of 12 years, what is the average distance between the two stars?
D^3= (m1+ m2) P^2
m1+m2= 5.5 M
p= 12
D= 9.25 AU
Explain how parallax measurements can be used to determine distances to stars.
Why can we not make accurate measurements of parallax beyond a certain distance?
Triangulation is used to measure the distance
The angle becomes so small that it isn’t measurable anymore.
The AU is defined as the average distance between Earth and the Sun, not the distance between Earth and the Sun. Why does this need to be the case?
The distance between Earth and the Sun changes due to Earth’s elliptical orbit.
The star Procyon is 3.5 pc away from the Earth. What is the parallax (in arcsecs) of Procyon as measured from the Earth?
p=1/d
p= 1/ 3.5 = 0.2857 arcsecs
distance modulus
calculation of distance from apparent and absolute magnitude
d= 10 x 10 ((m - M)/ s)
m: apparent mag
M: absolute mag
10 x 10 ( (12-20)/ 5) = 0.251 pc
Describe how the 21-cm line of hydrogen is formed. Why is this line such an important tool for understanding the interstellar medium?
The line happens when neutral hydrogen spin flips, which emits a photon at a 21cm wavelength that radio signals can pass. With neutral hydrogen being everywhere, the line can be used to map out the galaxy.
What causes reddening of starlight? Explain how the reddish color of the Sun’s disk at sunset is caused by the same process.
The dust and gas surrounding the star scatters the shorter wavelengths, which are blue, leaving the longer wavelengths, that are red.
When the Sun sets, it’s near the horizon, so it’s light travels through the thicker Earth atmosphere that has more dust and particles that scatter the blue wavelengths, and leave red wavelengths.
Suppose that, instead of being inside the Local Bubble, the Sun were inside an H II region. What would the night sky look like at various wavelengths?
Other wavelengths would look brighter but at visible, the sky would look like its glowing red.
Why is star formation more likely to occur in cold molecular clouds than in regions where the temperature of the interstellar medium is several hundred thousand degrees?
Cold molecular clouds have colder environments and lower pressure, this can allow stars to gravitationally collapse more easily.
Describe how the T Tauri star stage in the life of a low-mass star can lead to the formation of a Herbig-Haro (H-H) object.
When particles are ejected they collide with surrounding gases and dust, this excited the material and makes it glow/ heat up.
Two protostars, one 10 times the mass of the Sun and one half the mass of the Sun are born at the same time in a molecular cloud. Which one will be first to reach the main sequence stage, where it is stable and getting energy from fusion?
The larger star, 10 times the mass of the Sun will reach main seq phase faster, as larger protostars have more gravitational forces that causes higher core temperatures.
Observations suggest that it takes more than 3 million years for the dust to begin clearing out of the inner regions of the disks surrounding protostars. Suppose this is the minimum time required to form a planet. Would you expect to find a planet around a 10(solar)MSun star?
No, because due to the star’s big size, the star would gravitationally attract more dust and form pretty fast, creating a lower amount of time for a planet to form.
Astronomers find that 90% of the stars observed in the sky are on the main sequence of an H–R diagram; why does this make sense? Why are there far fewer stars in the giant and supergiant region?
Main seq is 90% of stars life vs giant and super giant are 10% of its life.
Why are star clusters so useful for astronomers who want to study the evolution of stars?
In clusters there are a bunch of stars that formed at the same time and that are close together.
Describe the two “recycling” mechanisms that are associated with stars (one during each star’s life and the other connecting generations of stars).
- hydrogen fuses into helium, and then helium fuses into carbon
- Ejected material (planetary nebulas) create star formation
What is a planetary nebula? Will we have one around the Sun?
A star dying and ejecting materials, and we will have one later around the Sun.
How do the two types of supernovae discussed in this chapter differ? What kind of star gives rise to each type?
Type IA: White dwarf is near a large star, such as a red giant, and it pulls material off the other star, causing the white dwarf to go over 1.4 solar mass, and creating a supernova
Type II: a giant mass star runs out of atoms to fuse in core, so it and collapses and “bounces,” creating a giant explosion, leaving a neutron star or black hole
How can the Crab Nebula shine with the energy of something like 100,000 Suns when the star that formed the nebula exploded almost 1000 years ago? Who “pays the bills” for much of the radiation we see coming from the nebula?
The rotation of the pulsar in the center of the nebula.
Arrange the following stars in order of their evolution:
1. A star with no nuclear reactions going on in the core, which is made primarily of carbon and oxygen.
2. A star of uniform composition from center to surface; it contains hydrogen but has no nuclear reactions going on in the core.
3. A star that is fusing hydrogen to form helium in its core.
4. A star that is fusing helium to carbon in the core and hydrogen to helium in a shell around the core.
5. A star that has no nuclear reactions going on in the core but is fusing hydrogen to form helium in a shell around the core.
- White dwarf, last
- Proto star, first
- Main sequence, second
- Big red giant, fourth
- Red giant, third
Say that a particular white dwarf has the mass of the Sun but the radius of Earth. What is the acceleration of gravity at the surface of the white dwarf? How much greater is this than g at the surface of Earth? What would you weigh at the surface of the white dwarf (again granting us the dubious notion that you could survive there)?
Use surface gravity formula,
g= GM/ r^2
Use G = 6.67 × 10^11
Times mass of sun: 2 x 10^30
Divide by the radius of earth,
r= 6.378 × 10^6
And then divide g by 9.8
If general relativity offers the best description of what happens in the presence of gravity, why do physicists still make use of Newton’s equations in describing gravitational forces on Earth (when building a bridge, for example)?
General reality is really only needed for huge objects since smaller objects are barely impacted
The Newton formulas work fine and are also more simple to use.
If a black hole itself emits no radiation, what evidence do astronomers and physicists today have that the theory of black holes is correct?
They look at the effect of the stars orbit and x-rays coming from the accretion disk
What is an event horizon? Does our Sun have an event horizon around it?
An event horizon is a boundary with an escape velocity at the speed of light. The Sun will never have an event horizon because it’s not big enough.
Why would we not expect to detect X-rays from a disk of matter about an ordinary star?
X-rays are very high energy, and an ordinary star’s energy is much lower
Explain where in a spiral galaxy you would expect to find globular clusters, molecular clouds, and atomic hydrogen.
- Globular cluster: Halo
- Molecular clouds: Disk and spiral arms
- Atomic hydrogen: disk and spiral arms
Suppose the Milky Way was a band of light extending only halfway around the sky (that is, in a semicircle). What, then, would you conclude about the Sun’s location in the Galaxy? Give your reasoning.
The Sun would be closer to the edge of the galaxy and therefore not making one side of the Milky Way as luminous.
The dwarf galaxy in Sagittarius is the one closest to the Milky Way, yet it was discovered only in 1994. Can you think of a reason it was not discovered earlier? (Hint: Think about what else is in its constellation.)
The black hole is obscuring our view
The Sun orbits the center of the Galaxy in 225 million years at a distance of 26,000 light-years. Given that a3=(M1+M2)×P2,
where a is the semimajor axis and P is the orbital period, what is the mass of the Galaxy within the Sun’s orbit?
a^3/ p^2 = galaxy solar mass
1 ly= 6.3 x 10^4 AU
26000(6.3 x 10^4)^3/ (2.25 x 10^8)^2
Describe the main distinguishing features of spiral, elliptical, and irregular galaxies.
Spiral: Disk and spiral arms
Elliptical: No spiral arms or disk
Irregular: Randomly shaped and has no familiar structure
What are the two best ways to measure the distance to a nearby spiral galaxy, and how would it be measured?
Cepheid variable and type 1a supernova
What does it mean to say that the universe is expanding? What is expanding? For example, is your astronomy classroom expanding? Is the solar system? Why or why not
It means space is expanding, the classroom and solar system are too small to be considered expanding.
Describe the arguments supporting the idea that quasars are at the distances indicated by their redshifts.
Quasars are moving very fast, at a fraction of the speed of light, and they never blue-shift, meaning they are only moving away.
Why could the concentration of matter at the center of an active galaxy like M87 not be made of stars?
The stars would collide with each other anyways and create a blackhole.
Difference of quasars vs stars
Quasars move very fast and stars don’t have jets, unlike quasars.
Why don’t any of the methods for establishing distances to galaxies, described in Galaxies (other than Hubble’s law itself), work for quasars?
Quasars can’t have supernova or cepheid cuz it’s a single object and not a star
If a quasar has a redshift of 3.3, at what fraction of the speed of light is it moving away from us?
v= (3.3 +1)^2 -1/ (3.3 +1)^2 +1
= 0.9c
What is the evidence that star formation began when the universe was only a few hundred million years old?
There’s spectral lines with elements higher than helium present in stars
Explain what we mean when we call the universe homogeneous and isotropic. Would you say that the distribution of elephants on Earth is homogeneous and isotropic? Why?
Homogenous: Any big volume will be similar to another sample of galaxies
Isotropic: From all directions there’s gonna be a similar structure
No for homo and iso
What is the evidence that a large fraction of the matter in the universe is invisible?
Gravitational lensing, fast moving gas emitting x-rays, and rotation rate of galaxies
Human civilization is about 10,000 years old as measured by the development of agriculture. If your telescope collects starlight tonight that has been traveling for 10,000 years, is that star inside or outside our Milky Way Galaxy? Is it likely that the star has changed much during that time?
It is probably the same and still in our galaxy.
