1 The Universe and Its Observations Free Online FlashCards

What is the observable universe?

The region of the universe from which signals have had time to reach us since the universe became transparent to light.

Why is the observable universe wider than its age in light-years?

Space expanded while the light traveled, so its distant source regions are now much farther away than the distance the light traveled.

What is the most distant light observed directly?

The cosmic microwave background (CMB), released when the early universe became transparent to light roughly 380,000 years after the Big Bang.

What does looking far into space reveal about time?

Looking at a distant object means seeing the light it emitted in the past. The time its light has traveled to reach us is its lookback time.

What distance does an astronomical unit represent?

An astronomical unit (AU) is approximately the average distance between Earth and the Sun, and is useful for distances within planetary systems.

What does a light-year measure?

A light-year is the distance light travels in one year, about 9.46 trillion kilometres. It measures distance, not time.

How does a parsec compare with a light-year?

A parsec is a distance unit equal to about 3.26 light-years. Kiloparsecs and megaparsecs represent thousands and millions of parsecs.

What can infrared and X-ray observations reveal?

Different wavelengths reveal different conditions: infrared can show objects hidden behind some dust clouds, while X-rays can trace extremely hot gas and energetic events.

What can spectral lines reveal about an object?

Their characteristic patterns can identify chemical elements and reveal physical properties such as temperature and density.

What is cosmological redshift?

Redshift is a shift toward longer wavelengths. For very distant galaxies, cosmological redshift occurs as expanding space stretches light during its journey.

Why do telescopes benefit from a larger collecting area?

A larger collecting area gathers more light, helping astronomers study faint objects.

What does photometry measure, and what is a light curve?

Photometry measures an object's brightness, often through selected wavelength filters. Repeated measurements form a light curve showing brightness changes over time.