21–40 of 50 results
Our expanding universe

Astronomy Questions & Answers

What is dark energy?

Cosmologists have invoked the concept of dark energy to explain the accelerated expansion of the universe, but the nature of dark energy remains one of the most pressing questions facing modern cosmology.

Astronomy Questions & Answers

Is there a center of the universe?

The universe began as a singularity that started expanding in the Big Bang. But the Big Bang was no regular explosion. Rather, space itself expanded, so there is no center of the entire universe. The observable universe, on the other hand, is a different story.

Astronomy Questions & Answers

How Many Galaxies Are There in the Universe?

Astronomers determine the number of galaxies in the universe by counting up the number visible in a tiny portion of the sky, and then accounting for all the regions of the observable universe. A 2013 study estimates that there are 225 billion galaxies in the observable universe.

Planck temperature map of universe

Science-based Q&A

What is the age of the universe?

Determining the age of the universe requires a knowledge of the universe's expansion rate, as well as its density and composition. Cosmologists currently set the age of the universe at about 13.77 billion years.

Science-based Q&A

The End of the Universe: What is our ultimate fate?

During the latter half of the 20th century, cosmologists narrowed the universe’s fate to three possibilities, and they all depend on its density.

Spacecraft and Space Missions

Rosetta's Comet has a Split Personality

The Rosetta spacecraft is closing in on Comet 67P/C-G, providing astronomers with an ever more detailed view of its structure. Judging by the latest photos, it actually has two components and is shaped like… a rubber ducky?

Science-based Q&A

What are constellations?

In 1930, the International Astronomical Union (IAU) divided the sky into 88 constellations. Each constellation is defined by an imaginary boundary on the sky and named after a classical star pattern within those boundaries. So when we say a star is “in” a particular constellation, we mean it lies within the IAU-defined boundaries of that constellation.

Cosmology

The Mystery of the Missing Light

Astronomers recently discovered that there is not nearly enough ultraviolet light from stars and quasars in the local universe to account for observations of intergalactic gas.

Science-based Q&A

How Many Stars are There in the Universe?

By measuring the number and luminosity of observable galaxies, astronomers put current estimates of the total stellar population of the observable universe at roughly 70 billion trillion.

Astronomy Questions & Answers

What is the brightest star in the sky?

The brightest star in the sky is Sirius, also known as the “Dog Star” or, more officially, Alpha Canis Majoris, for its position in the constellation Canis Major.

Astronomy Questions & Answers

How Do Stars Die and How Long Do Stars Live?

Both the life and death of a star depend on its mass. Generally speaking, the more massive a star, the faster it burns its fuel and the shorter its life. The most massive stars meet their end in a supernova explosion after only a few million years of fusion, while the tiniest stars continue to feebly burn for upwards of a trillion years.

Science-based Q&A

What Is a Star?

A star is a luminous ball of gas held together by its own gravity. Nuclear fusion in its core supports the star against gravity and produces photons and heat. The Sun is the closest star to Earth.

Astronomy Questions & Answers

Why Do Stars Twinkle?

Though it wouldn’t work so well in the nursery rhyme, a star’s twinkling actually has a technical term, astronomical scintillation: the effect of our planet’s atmosphere on starlight.

Science-based Q&A

Asteroids: What Are They and Where Do They Come From?

Asteroids are rocky objects leftover from the solar system's formation, found primarily in the asteroid belt, a region of the solar system in between the orbits of Mars and Jupiter.

Comet ISON (C/2012 S1)

Science-based Q&A

Comets: What Are They? Where Do They Come From?

Comets are suspected to be remnants of planet formation in the solar system about 4.6 billion years ago and primarily originate in the Kuiper Belt and the Oort Cloud.

Science-based Q&A

Why do comets have tails?

Comets develop tails as they approach perihelion—the place in their orbits when they are closest to the sun. The sun’s heat causes some of the material in a comet to vaporize, which in turn releases dust particles that were trapped in the ice.

Science-based Q&A

How big is the Sun?

The Sun is more than 330,000 times as massive than the Earth. It has a diameter of nearly 1.4 million kilometers (865,000 miles), and its volume could enclose about 1.3 million Earths.

Space weather

Science-based Q&A

What is the solar wind?

The Sun’s outer atmosphere, the corona, is the source of the solar wind, a steady outflow of charged particles from the Sun.

Eight planets await

Science-based Q&A

What Is the Smallest Planet and Largest Planet in our Solar System?

When it comes to both mass and volume, Jupiter is the largest planet in the solar system, while Mercury is the smallest.

Astronomy Questions & Answers

What is a meteor shower?

Meteor showers occur when Earth passes through a stream of meteoric material. The brief streaks of luminescence we call meteors are caused by meteoroids burning up as they pass through the atmosphere.

Advertisement
Advertisement
Advertisement
Advertisement