The disk of the Milky Way galaxy contains roughly 200 billion (1 billion = 109 ) stars. The disk is not solid, but rather is a volume about 100,000 light-years in diameter (1 ly = 9500 billion kilometers) and 1000 light-years in thickness. What is the number density of stars in the Milky Way galaxy disk, in units of stars per cubic light-year? How about in units of stars per cubic km?

The disk of the Milky Way galaxy contains roughly 200 billion (1 billion = 109 ) stars. The disk is not solid, but rather is a volume about 100,000 light-years in diameter (1 ly = 9500 billion kilometers) and 1000 light-years in thickness. What is the number density of stars in the Milky Way galaxy disk, in units of stars per cubic light-year? How about in units of stars per cubic km?

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In the reading, you were told that there were roughly 10,000 galaxies in the image of the Hubble Ultra Deep Field alone. The image is roughly 10 square arcminutes and there are roughly 1.5*10^8 square arcminutes composing the entire sky. With that in mind and assuming that the Hubble Ultra Deep Field represents an average part of the sky, roughly how many galaxies may exist in the observable universe? (Please include commas for every factor of 1,000; for example 2,343,567,890)
Assume that a typical galaxy contains about 200 billion stars and that there are more than 150 billion galaxies in the known universe. Estimate the total number of stars in the universe.
A) A typical dust grain has a radius of about 0.1 micrometers and a mass of 10-14 grams. Roughly how many dust particles are in a cloud containing 1000 Msun of dusty gas if 1% of the cloud's mass is in the form of dust grains? B) What surface area would be covered by these grains if you put them side by side? Assume these grains are spherical. Answer in square light-years. C) Estimate the total surface area covered by the cloud assuming it's matter density is like that of a typical molecular cloud, about 10-21 g/cm3 (Hint: first calculate the clouds volume from it's mass and density, then determine its radius using the formula for volume of a sphere) Answer in square light-years. D) Comparing all above answers, What are the chances (very roughly) that a photon passing through the cloud will hit a dust grain?
If the Sun's mass is about average, how many stars are there in the Milky Way galaxy? The mass of the Sun is of the order of 1030 kg and the mass of the Milky Way galaxy is of the order of 1042 kg.
Another explanation for the Universe is the Steady State Hypothesis. The Steady State Hypothesis says that the Universe has always existed and is infinite in extent. Which of the following supports the Big Bang Theory and which supports the Steady State Model. (Select B-Big Bang Theory, S-Steady State Model, If the first is B and the rest S, enter BSSSSS). A) An observation that some globular clusters show M-type stars that have evolved off the main sequence. B) The measurement of redshifts that show galaxies appear to be moving away from each other and the Universe is expanding. C) A measurement that shows the density of the Universe is close to the critical density. D) The measurement of the microwave background radiation. E) Observing that galaxies at very large distances look identical to those in the nearby universe.
can you please solve number 5 showing step by step on a picture. Show all your work and explain step by step on a PICTURE PLEASE. Please post a picture don't type it, it's hard to understand!
If the speed of light is given as 299,792,458 meters per second and the wavelength is 560 nm. what is the frequency of this light? Give your answer in THz!
T/ F The distance unit best for interstellar distances is the light-year. ___ The distance unit best for intergalactic distances is the mega-parsec. ___
If Jim could drive a Jetson's flying car at a constant speed of 330 km/hr across oceans and space, approximately how long (in millions of years, in 106 years) would he take to drive to a nearby star that is 8.7 light-years away? Use 9.461 × 1012 km/light-year and 8766 hours per year (365.25 days).
The Universe is approximately 13.8 Billion years old. What is the volume of the visible universe in m3?
Figure 2 shows the "rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 -4 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should…