What is the cosmic distance ladder?

A literal ladder-shaped structure astronomers use to climb to higher altitudes for better observations A set of overlapping techniques, each valid at different distances, that astronomers chain together to measure distances across the universe A mathematical formula that gives the distance to any galaxy from its color alone A ranking of galaxies by distance, from the nearest to the farthest known

What is a Cepheid variable star, and why is it useful for measuring distances?

A star that changes color, and the color indicates how far away it is A star that pulsates regularly; its period of pulsation reveals its true luminosity, allowing distance to be calculated by comparing true and apparent brightness A very old star whose age can be used to estimate how far it has traveled from its birthplace A binary star whose eclipses allow astronomers to measure the size and distance of the system

What did Edwin Hubble prove in 1923-1924 using Cepheid variable stars?

That Andromeda was part of the Milky Way, resolving the island universes debate in favor of one galaxy That the universe was infinite and contained no distinct galaxies That the Andromeda Nebula was a separate galaxy far beyond the Milky Way, settling the Great Debate about island universes That Cepheid stars could only be used to measure distances within the Milky Way

Who discovered the period-luminosity relationship for Cepheid variable stars?

Edwin Hubble, in 1929 Vesto Slipher, in 1912 Henrietta Swan Leavitt, in 1912 Carl Sagan, in 1980

Why are Type Ia supernovae called standard candles?

They emit light of only one specific wavelength, like a laser They are always the same physical size, so their apparent size gives their distance They all reach the same peak luminosity when they explode, so comparing their apparent brightness to their known true brightness gives their distance They produce standard amounts of a radioactive element whose decay rate gives the distance

What is the Tully-Fisher relation?

A formula relating a galaxy's size to its distance A correlation between how fast a spiral galaxy rotates and how intrinsically luminous it is, usable as a distance indicator A relationship between the number of Cepheid stars in a galaxy and that galaxy's distance A formula that connects a galaxy's redshift directly to its physical size

What does the Hubble constant H0 of approximately 70 km/s/Mpc mean?

The universe expands by 70 km in every second For every megaparsec of distance, a galaxy appears to recede from us about 70 km/s faster Every megaparsec of space contains about 70 galaxies The Milky Way moves through space at 70 km/s

What is the Hubble tension?

The difficulty of pointing the Hubble Space Telescope precisely enough to measure galaxy distances A significant discrepancy between different methods of measuring H0 — the CMB gives about 67 km/s/Mpc while Cepheids and supernovae give about 73 km/s/Mpc The fact that no galaxy closer than 1 megaparsec obeys the Hubble Law The argument between Hubble and other astronomers in the 1920s about whether galaxies were inside or outside the Milky Way

Why does redshift become a useful distance indicator for very distant galaxies?

More distant galaxies have older stars that glow redder The interstellar dust between galaxies reddens their light proportional to distance More distant galaxies are receding faster due to the expansion of space, producing larger redshifts that can be related to distance via Hubble's Law Redshift only works for galaxies inside the Local Group

Who first measured the recession velocities of many galaxies before Hubble combined them with distances?

Albert Einstein, using general relativity equations Vesto Slipher, who measured the redshifts of many spiral nebulae between 1912 and 1917 Henrietta Swan Leavitt, using Cepheid light curves George Lemaitre, in his 1927 paper on the expanding universe