Ask Astro | Astronomy.com

A diagram illustrating the outer solar system from an angled top-down perspective. Concentric orbital paths are shown around a central yellow Sun, with Jupiter, Saturn, Uranus, and Neptune labeled at increasing distances. Pluto is shown in yellow text outside Neptune's orbit, and the entire outer region is surrounded by a diffuse haze representing the Kuiper Belt, labeled in white text.

How do planets clear out objects on the other side of their orbit?

A size comparison illustration showing Earth and the Moon side by side against a black background. Earth appears on the left, showing the Americas, swirling cloud cover, and blue oceans, while the gray, crater-marked Moon is shown to the right at roughly one-quarter of Earth's diameter, accurately reflecting their relative sizes.

How is the Moon 1% of Earth’s mass, but its gravity is 17% of Earth’s?

A black and white photograph of a total solar eclipse. The Moon appears as a dark circular disk at center, surrounded by the Sun's glowing white corona extending outward in streaks and rays — most prominently upward and to the lower left. The background is nearly black, emphasizing the dramatic contrast of the corona's light.

Science, Solar System

Why is the Moon exactly the same apparent size from Earth as the Sun?

Side-by-side grayscale comparison of the Moon's two hemispheres. The left image shows the familiar near side of the Moon, featuring large dark volcanic plains called maria that give it a distinctive mottled appearance. The right image shows the far side of the Moon, which lacks significant maria and instead appears more uniformly cratered and bright, with prominent crater ray systems radiating outward from impact sites.

Science, Solar System

Why does one side of the Moon have a lot of craters, while the other does not?

X-ray and optical composite image of IGR J11014-6103, a pulsar wind nebula, from the Chandra X-ray Observatory. A large, diffuse cloud of magenta/pink X-ray emission dominates the upper left, representing a supernova remnant. To the lower right, a smaller bright green and pink structure shows a pulsar with jets and a curved tail of X-ray emission trailing behind it, indicating rapid motion through space. Background stars are visible throughout. Credit: Chandra X-ray Center (chandra.si.edu).

What does the term ‘supersonic’ mean in astronomy?

A close-up photograph of two hands cradling a dark, angular meteorite. The rock is roughly fist-sized with a black, slightly textured fusion crust and irregular flat faces, characteristic of a chondrite meteorite.

How can I get a rock tested to see if it’s a meteorite?

An artist's illustration of two stars against a dense, starry background with red and blue nebula clouds. A large, intensely bright white star dominates the left side of the image, while a smaller, vivid blue star glows to its right, suggesting a binary star system.

How can a young blue giant have a white dwarf companion star that’s billions of years older?

Did time move slower right after the Big Bang?

Why do some stars appear to twinkle while others don’t?

What would Earth be like if there were no Moon?

Abell 1689

When gravitational lensing occurs, can we see the object doing the lensing?

Human Spaceflight

With renewed interest in going to the Moon, how will future trash be dealt with?