Astronomy Exam 2 Part 4

Based on the rotation curves of stars in spiral galaxies and the Milky Way, it is believed that most of the mass in galaxies is in the form of dark matter. This is because the observed rotation curves do not match the expected rotation curves based on the visible matter alone. Dark matter is an invisible substance that does not interact with light, but its gravitational effects can be detected. Therefore, the presence of dark matter is inferred to explain the observed rotation curves and account for the missing mass in galaxies.

Light travels at a finite velocity and takes time to reach us. This means that the light we receive from distant objects has traveled for a certain amount of time before reaching our eyes. Since the speed of light is not infinite, the light from these objects takes a significant amount of time to reach us. Therefore, when we observe distant objects, we are actually seeing them as they appeared in the past, because the light we see has taken time to travel to us.

Dark matter refers to mass that is inferred to exist based on its gravitational effects, but does not emit any visible light or other detectable radiation. This means that dark matter cannot be directly observed or detected using ordinary methods of observation. It is believed to make up a significant portion of the total mass in the universe, and its presence is necessary to explain various astronomical observations and the structure of galaxies. Options A, B, and C do not accurately describe dark matter, making option D the correct answer.

The correct answer is E. density. The open, closed, or flat nature of the universe depends on its overall density. If the density is high enough, the universe is closed and will eventually collapse in on itself. If the density is too low, the universe is open and will continue to expand forever. If the density is just right, the universe is flat and will also continue to expand forever, but at a decreasing rate. Luminosity, temperature, radius, and rotation rate do not determine the overall nature of the universe.

Cepheid variable stars are used by astronomers to measure galaxies' distances because their luminosity can be determined from their period of variation. Cepheids are pulsating stars that vary in brightness over a regular period of time. The period of variation is directly related to the star's intrinsic luminosity, allowing astronomers to calculate their distance based on the observed brightness. This relationship between period and luminosity has been well-established and is used as a standard candle for distance measurements in astronomy.

Hubble's law states that the universe is expanding, which is option A. It also allows us to measure the distances to distant galaxies and quasars, which is option B. Additionally, Hubble's law implies that the universe had a beginning about 15 billion years ago, which is option C. Lastly, the law states that more distant galaxies recede more rapidly than nearby ones, which is option D. Therefore, the correct answer is E, all of the above, as all the statements are supported by Hubble's law.

The correct answer is D. the Big Bang. During the Big Bang, the Universe underwent a rapid expansion and cooling. This allowed for the formation of light elements such as helium, which is believed to have been produced in abundance during this early stage of the Universe. As the Universe continued to evolve, helium was then incorporated into the formation of stars and other celestial bodies. Therefore, the majority of helium in the Universe is thought to have originated from the Big Bang.

Edwin Hubble recognized that the Andromeda nebula was a separate "island universe" rather than a component of our own galaxy because he used Cepheid variables to find it was a tremendous distance away. Cepheid variables are stars that pulsate in a regular pattern, and their brightness is directly related to their period of pulsation. By observing the brightness of Cepheid variables in the Andromeda nebula, Hubble was able to determine their true brightness and calculate their distance. He found that the Andromeda nebula was much farther away than any known stars in our galaxy, indicating that it was a separate entity.

Spiral galaxies are known to rotate by measuring the Doppler shifts of stars on each side of its center. The Doppler shift occurs when an object is moving towards or away from an observer, causing a shift in the wavelength of the light it emits. By measuring the Doppler shifts of stars on each side of its center, astronomers can determine the rotational motion of the galaxy. This method allows them to understand the dynamics and structure of spiral galaxies.

An astronomer living in another galaxy would see the same relation between redshift and distance that we observe. This is because the redshift of light from distant objects is caused by the expansion of the universe, which affects all galaxies regardless of their location. As objects get farther away, their light is stretched to longer wavelengths, resulting in a redshift. This redshift is directly related to the distance of the object, meaning that the farther the object, the greater the redshift. Therefore, an astronomer in another galaxy would observe a similar relationship between redshift and distance as we do.