Explain how we estimate that there are about 50-100 billion galaxies in the observable universe
What will be an ideal response?
Obviously it's impossible to count so many galaxies one by one, but by observing a small part in detail, we can extrapolate to get the total number. As an example, the Hubble deep field shows thousands of galaxies in a very small angular area of the sky (about equal to the size of a grain of sand held at arm's length). Multiplying the number of galaxies by the ratio of the angular area of the entire sky to the angular area of the deep field then gives an estimate of the total number of galaxies in the observable universe.
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Radioactive Decay: An air sample is contaminated with 15O, which has a half-life of 2.03 minutes. You can pass it through a long pipe to allow it to decay until it can be safely released into the atmosphere. If the speed of the gas in the pipe is 1.1 m/s, how long must the pipeline be for the sample to decay to 3.0% of its original activity?
A. 680 m B. 8.0 m C. 72 m D. 250 m
Which of the following statements best describes the idea behind the Carbon Assimilation Experiment on board the Viking landers?
A) living organisms in the soil should incorporate carbon from atmospheric gases B) radioactive gases should be produced when radioactive nutrients are added to a soil sample C) soil with living organisms in it should contain organic molecules D) living organisms in the soil should give off gases when they metabolize nutrients
In the upper atmosphere at altitudes where commercial airlines travel, we find extremely cold temperatures. What is the speed of sound (in metric units) for a temperature of -53.0 oC?
At the maximum height of a projectile launched at an angle to the horizontal, the projectile's velocity is in a ______________ direction
Fill in the blank(s) with correct word