Hubble’s Law describes how galaxies move away from each other, with farther galaxies moving faster. This is based on redshift observed through spectroscopy. The Hubble constant reflects the rate of expansion and is used in cosmology, but values vary. Data may be inaccurate due to indirect measurement.
Hubble’s law is a description of an observation made by Edwin Hubble in 1929. Hubble noticed that objects in the universe appeared to be moving away from each other and that the farther away a galaxy was from an observer, the faster it would move . This observation is used as the basis for the Hubble constant, an estimate of the rate of expansion of the galaxy that is an important concept in cosmology, used to support a number of discussions about the nature of the universe. The Hubble constant is actually better referred to as the “Hubble variable,” because it depends on time.
The observations made by Hubble relied on the use of spectroscopy to observe the redshift of the galaxies it was observing. Redshift, the result of the Doppler shift, which causes a wave to change frequency as the object emitting the wave moves relative to the observer, is a shift in the spectrum of light emitted from a galaxy towards the far spectrum red. Redshift occurs when galaxies move away from the observer. Galaxies moving towards an observer undergo a so-called blueshift, with the light moving towards the blue end of the spectrum.
Hubble’s observations led him to understand that the galaxies were moving away from each other and, moreover, that the farther away a galaxy was, the faster it was moving. This is the foundation of Hubble’s Law and a backbone of the expanding universe theory. It’s important to be aware that this phenomenon can be observed from anywhere in the universe. The universe, it turns out, has a lot in common with a poppy seed muffin: As the universe/muffin expands, the galaxies/poppy seeds within recede from each other.
Hubble’s law is sometimes expressed with this equation: V=H0D. The equation reflects the relationship between speeds, determined with the aid of spectroscopy; the Hubble constant, which reflects the rate of expansion occurring in the universe; and distance. Cosmologists have come up with different values for the Hubble constant. It is believed that the most accurate values were determined with the assistance of the famous telescope named after Hubble. The Hubble constant in 2009 is thought to be about 74 kilometers per second for every megaparsec of distance.
Speed and distance cannot be measured directly. This means that data obtained with the assistance of Hubble’s law may be incorrect. Indeed, there have been heated discussions since 1929 about Hubble’s Law and its implications for the nature of the universe.
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