Blog topic
Astronomy & Space articles
Black holes, how stars form, what a light year measures, why the Moon has phases, and how a telescope really works. The recurring theme is scale: how astronomers measure distances they can never travel, and why looking far out means looking back in time.
26 explainers, newest first. Each one ends with real questions from the unit that teaches it, so you can read the explanation and then check whether it stuck.
These are the readable companion to the Astronomy & Space track, which holds 18 units and 2,159 practice questions. If you are starting the subject rather than looking something up, the study guide is the better place to begin.
What Is a Pulsar? A Lighthouse Made of a Dead Star
A pulsar is a spinning neutron star that sweeps a beam of radio waves across the Earth with each turn, ticking like a clock. What makes it pulse.
October 29, 20268 min readWhat Is a Meteor Shower? Comet Dust Hitting the Sky on Schedule
A meteor shower is the Earth passing through the dust a comet left along its orbit, so grains burn up by the dozen each hour. Why they recur, and how to watch.
October 18, 20268 min readWhat Are Asteroids? Leftovers of the Solar System and the Odds of a Hit
Asteroids are rocky and metallic bodies, mostly between Mars and Jupiter, left over from the solar system's birth. What they are and the odds of a hit.
October 15, 20267 min readWhy Does the Moon Always Show the Same Face?
The Moon rotates once per orbit, so the same side always faces Earth. How tides locked it in place, what the far side looks like, and why it is not dark.
October 14, 20268 min readWhat Is the Milky Way? Our Home Galaxy Seen From the Inside
The Milky Way is the galaxy the Sun belongs to, a disc of a few hundred billion stars. What it is made of, where we sit in it, and how its shape was mapped.
October 12, 20268 min readWhat Is a Neutron Star? A Sun Squeezed Into a City
A neutron star packs more than the Sun's mass into a ball twenty kilometres across. How it forms, what its matter is like.
October 9, 20267 min readWhat Is a Nebula? The Clouds Where Stars Are Born and Die
A nebula is a cloud of gas and dust in space. Some are nurseries where stars form, some are the shed layers of dying stars, a few are exploded wreckage.
October 7, 20267 min readWhat Are Saturn's Rings Made Of? Ice, Gaps and a System That May Be Young
Saturn's rings are almost pure water ice, from dust grains to house-sized boulders, in a sheet wider than the Earth-Moon gap. What they are and how they formed.
October 5, 20268 min readWhat Are Exoplanets and How Are They Found?
Thousands of planets are now known around other stars. How astronomers detect worlds they cannot see, what kinds have turned up, and where the nearest ones are.
October 3, 20269 min readHow Was the Moon Formed? The Giant Impact and the Evidence for It
The Moon is thought to be the debris of a collision between the young Earth and a Mars-sized body. What the Apollo rocks showed, and what still does not fit.
October 1, 20269 min readHow Do We Measure Distances in Space? Parallax, Cepheids and the Cosmic Ladder
Nobody has a tape measure to the stars. How parallax, Cepheid variables and exploding stars form a ladder of methods, each calibrated on the one below.
September 29, 20268 min readHow the Sun Makes Its Energy: Fusion at the Heart of a Star
The Sun is not burning. Deep in its core, hydrogen nuclei are fused into helium, and the small mass lost in each fusion is what lights the solar system.
September 9, 20268 min readWhy Pluto Is No Longer Called a Planet
In 2006 astronomers finally defined the word planet, and Pluto did not fit. From its 1930 discovery to the rival world found in 2005 and the 2015 flyby.
September 9, 20267 min readWhat Is a Black Hole?
How gravity gets strong enough to trap light, what the event horizon is, and how astronomers found and photographed them.
August 28, 20269 min readHow Do Stars Form?
From cold gas clouds to nuclear fusion, here is the full sequence that turns a drifting cloud into a shining star.
August 28, 20269 min readWhat Is a Light Year?
Why it measures distance and not time, how far it actually is, and why looking at the sky means looking into the past.
August 28, 20269 min readWhy Does the Moon Have Phases?
Why does the moon have phases? It is not Earth's shadow. Here is how the changing angle of sunlight produces the full cycle from new moon to full.
August 28, 20269 min readWhat Is the Big Bang Theory?
What it actually claims, the three main lines of evidence for it, and the common misunderstandings worth clearing up.
August 28, 20269 min readWhat Are the Planets in Order?
What are the planets in order from the Sun? A quick tour of all eight, what makes each distinct, and what happened to Pluto.
August 28, 202610 min readHow Do Telescopes Work?
The difference between lenses and mirrors, why aperture matters more than magnification, and how modern observatories see so far.
August 28, 202610 min readWhat Is a Comet Made Of?
Ice, dust and rock, why comets grow tails near the Sun, and where they come from in the outer solar system.
August 28, 20269 min readWhat Is Gravity?
From Newton's force to Einstein's curved spacetime, why everything falls at the same rate, and what we still do not understand.
August 28, 20269 min readCould There Be Life on Other Planets?
What scientists actually look for, the most promising places in our own solar system, and why we have found nothing yet.
August 28, 20269 min readWhat Is a Supernova?
How stars explode, the two main types, and why every heavy element in your body came from one.
August 28, 20269 min readWhat Is Dark Matter?
Why galaxies spin too fast to hold together, the evidence for invisible mass, and the honest state of the search.
August 28, 202610 min readLook Up: A Beginner's Guide to Astronomy
Astronomy begins with your own eyes and a dark sky. Meet the Moon, the planets, and the stars, and let simple wonder come before the big numbers.
December 27, 20257 min read