Observational cosmology

People study the whole sky.

They use tools to see far away. These tools help us see stars and far lands. One tool is a big telescope. Scientists use it to see things that are very far. They found out the sky is much bigger than our own home.

They can even see how the sky moves. This helps us learn how the sky began. It is a big, grand place to learn about.

Scientists study the whole universe. They want to know how it began. They also want to know how it changes. This study is called observational cosmology.

To do this, they use tools like telescopes. Long ago, people thought our Milky Way was the whole universe. But Edwin Hubble used a big telescope to find out more. He found special stars called Cepheid variables. These stars help us measure how far away things are. Hubble saw that other galaxies were very far away. This showed that the universe is much bigger than we thought.

Scientists also look for light from the start of time. This is called the cosmic microwave background. It is a faint glow left over from the Big Bang.

Two scientists named Arno Penzias and Robert Wilson found it. They used a special radio tool to detect it.

Today, we use maps to see the sky. These maps show where dark matter is. Dark matter is a type of stuff we cannot see. It helps galaxies form.

New tools like the James Webb Space Telescope help us see even more. We are still learning about our big home.

Observational cosmology is a way of studying the universe. Scientists look at how it began and how it changes. They use tools like telescopes and cosmic ray detectors to see things. This helps them learn about the structure of everything in space.

By watching the sky, they can find out where we fit in the cosmos. It is a way to turn looking into learning.

Measuring distance in space is a hard job. Astronomers use a method called a cosmic distance ladder. One way is using stellar parallax for nearby stars. However, that is too hard for things far away. In 1908, Henrietta Swan Leavitt found Cepheid variables. These are special stars that help measure distance. Edwin Hubble used these stars to find spiral nebulae. He used the 100-inch Hooker Telescope at Mount Wilson Observatory. This proved these objects were outside our Milky Way galaxy.

History shows how our ideas grew over time. Long ago, the philosopher Immanuel Kant wrote about the heavens. Later, the Shapley-Curtis debate helped define the subject. In 1927, Georges Lemaître used measurements to estimate a constant. He linked galaxy distance to how fast they move away. Two years later, Hubble showed a positive correlation. This is known as Hubble's law. It is the base for theories about an expanding universe. David Schramm called the 1990s the "Golden Age of Cosmology."

Scientists also look for clues in light and heat. They use spectroscopy to find chemical elements. For example, helium was first seen in the Sun. In 1965, Arno Penzias and Robert Wilson found something amazing. They used a Dicke radiometer at Bell Telephone Laboratories. They found the cosmic microwave background. This is a faint glow from the Big Bang. They won the Nobel Prize in 1978 for this discovery.

Today, we use many tools to map the sky. Redshift surveys help us see the 3D shape of matter. The Sloan Digital Sky Survey aims to measure 100 million objects. We also use infrared tools like the Spitzer Space Telescope. The James Webb Space Telescope will explore the infrared too. These tools help us study dark matter and dark energy.

We use these maps to understand the large-scale structure of space.

Observational cosmology is the scientific study of the universe's origin, evolution, and structure. Instead of relying only on math, scientists use physical observations to understand the cosmos. They use advanced instruments like telescopes and cosmic ray detectors to gather data. This field helps us understand how the universe began and how it changes over time. By observing distant objects, cosmologists can test different theories about the nature of space.

Measuring distances in space is a difficult process due to high measurement uncertainty. Astronomers use a method called the cosmic distance ladder to reach further into space. For nearby stars, they use stellar parallax, which involves measuring a star's slight shift in position. However, this method fails for objects far beyond our own galaxy. In 1908, Henrietta Swan Leavitt discovered Cepheid variables, which act as standard candles. These are stars with predictable brightness that allow astronomers to calculate distance. Edwin Hubble used the 100-inch Hooker Telescope at Mount Wilson Observatory to find these stars in spiral nebulae. This proved those nebulae were separate galaxies located well outside the Milky Way.

These discoveries helped establish the scale of the universe and settled the Shapley-Curtis debate. In 1927, Georges Lemaître combined various measurements to estimate a constant of proportionality. He linked the distance of galaxies to their recessional velocities, or how fast they move away. Lemaître found a value of about 600 km/s/Mpc. Two years later, Hubble found a positive correlation with a slope of about 500 km/s/Mpc. This relationship is known as Hubble's law. It provides the observational foundation for the theory of an expanding universe.

Scientists also study the universe by looking at the chemical makeup of celestial objects. They use spectroscopy to identify elements by looking at light patterns. These patterns show emission and absorption lines caused by electronic transitions in atoms. For example, the element helium was first identified through its spectroscopic signature in the Sun. This happened before the gas was even isolated on Earth. By comparing these light patterns to the composition of meteorites, scientists can compute the relative abundances of elements in space.

One of the most important discoveries was the cosmic microwave background, or CMB. This is a faint glow of radiation left over from the hot Big Bang. The CMB was predicted in 1948 by George Gamow and Ralph Alpher. In 1965, Arno Penzias and Robert Wilson were using a Dicke radiometer at Bell Telephone Laboratories. They found an unexpected excess antenna temperature of 3.5 K that they could not explain. They eventually realized this was the CMB radiation. This discovery earned them the Nobel Prize in Physics in 1978.

Modern cosmology uses many different types of observations to refine our models. Redshift surveys map the 3D distribution of matter by combining redshift data with angular positions. The Sloan Digital Sky Survey (SDSS) is a major ongoing project aiming to measure 100 million objects. Other surveys, like the 2dF Galaxy Redshift Survey, have measured redshifts for over 220,000 galaxies. These surveys help reveal large-scale structures, such as the Great Wall, which is a supercluster over 500 million light-years wide.

Astronomers also use different wavelengths of light to see the universe. Radio astronomy uses bright radio galaxies to probe extreme distances and early cosmic times. Infrared astronomy is vital because much of the infrared light is blocked by Earth's atmosphere. Scientists use space-based tools like the Spitzer Space Telescope or the James Webb Space Telescope to study these wavelengths. These observations have helped scientists discover dark matter and dark energy. Today, these findings are organized into the Lambda-CDM model, which explains how the universe evolves based on its constituent materials.