OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~347 words · 2 min

Two Families of Star Clusters Stars rarely form alone. A giant cloud of gas and dust can collapse into hundreds, thousands, or even millions of stars at once, all born together and held in place by their combined gravity. Astronomers sort t

Astronomy

Astronomy · L2 · Star Clusters

@openstem

Note~376 words · 2 min

What Is Light Pollution? Light pollution is excessive or misdirected artificial light that brightens the night sky far beyond its natural darkness. It comes from streetlights, buildings, signs, and homes — especially fixtures that send ligh

Astronomy

Astronomy · L2 · Light Pollution and Dark Skies

@openstem

Note~287 words · 1 min

Born From a Cloud of Gas Stars begin their lives inside nebulae — enormous clouds of gas and dust drifting through a galaxy. Gravity slowly pulls together the densest clumps of gas, and as material falls inward, the clump heats up and spins

Astronomy

Astronomy · L2 · The Life Cycle of Stars

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Note~266 words · 1 min

One Cloud, One Family About 4.6 billion years ago, the Sun and every planet in our Solar System formed together out of a single giant cloud of gas and dust, called a solar nebula. This idea — that the Sun and planets share a common origin —

Astronomy

Astronomy · L2 · How the Solar System Formed

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Note~292 words · 1 min

Escaping the Atmosphere Earth's atmosphere is wonderful for breathing, but it makes life difficult for astronomers. It blurs and distorts starlight — the reason stars appear to twinkle — and it completely blocks many kinds of light before t

Astronomy

Astronomy · L2 · Space Telescopes

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Note~296 words · 1 min

Two Kinds of Shadow Any object blocking a light source casts a shadow with two distinct parts: an umbra, the fully dark region where the light source is completely blocked, and a penumbra, the surrounding region where the light source is on

Astronomy

Astronomy · L2 · Eclipse Mechanics: Umbra, Penumbra, and Types

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Note~232 words · 1 min

Leftovers From Planet Formation Not every piece of material in the young Solar System ended up inside a planet. Two great regions still hold enormous numbers of smaller leftover bodies today: the asteroid belt and the Kuiper Belt. The Aster

Astronomy

Astronomy · L2 · The Asteroid Belt and Kuiper Belt

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Note~212 words · 1 min

Interactive Astronomy Plots The Astronomy Visualised collection contains interactive graphs that let you explore fundamental astronomical relationships by adjusting parameters in real time. Hubble's Law The Hubble Law plot shows recession v

Astronomy

Astronomy · L3 · Interactive Astronomy: Exploring the Universe with Graphs

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Note~226 words · 1 min

Three Laws, One Elegant Pattern Before Newton explained why planets orbit the way they do, Johannes Kepler worked out, from decades of observational data, exactly how they move. His three laws, published in the early 1600s, still describe o

Astronomy

Astronomy · L3 · Kepler's Laws & Orbital Mechanics

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Note~280 words · 1 min

One Law, Every Falling Thing Isaac Newton's great insight was that the force pulling an apple to the ground and the force holding the Moon in orbit are the same force, obeying the same rule everywhere in the Universe. The Law of Universal G

Astronomy

Astronomy · L3 · Newtonian Gravitation

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Note~292 words · 1 min

Sorting Stars by Their Light Every star's spectrum — the pattern of colours and dark absorption lines in its light — encodes its surface temperature. Astronomers use that spectrum to sort stars into seven main classes, from hottest to coole

Astronomy

Astronomy · L3 · Stellar Classification

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Note~304 words · 2 min

A Star's Life Is Written by Its Mass Every star begins the same way — a collapsing cloud of gas and dust — but from there, its mass decides almost everything else: how long it lives, how it dies, and what it leaves behind. Birth: From Cloud

Astronomy

Astronomy · L3 · Stellar Evolution

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Note~290 words · 1 min

An Expanding, Cooling Universe The Big Bang model holds that the observable Universe began about 13.8 billion years ago in an extremely hot, dense state and has been expanding and cooling ever since. It is not an explosion of matter into em

Astronomy

Astronomy · L3 · The Big Bang & Cosmology

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Note~304 words · 2 min

Most of the Universe Is Invisible Ordinary matter — atoms, stars, planets, everything we can see and touch — makes up only about 5% of the Universe's total mass-energy. The rest is split between two poorly understood components: dark matter

Astronomy

Astronomy · L3 · Dark Matter & Dark Energy

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Note~250 words · 1 min

Sorting Galaxies by Shape Edwin Hubble classified galaxies by their visual shape into a scheme still used today, sometimes called the 'Hubble tuning fork' for the shape of its diagram. Spirals are rich in gas and dust and actively forming n

Astronomy

Astronomy · L3 · Galaxy Types & the Milky Way

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Note~296 words · 1 min

Finding Planets We Cannot See Directly Exoplanets are enormously faint compared to their host stars, so astronomers have developed several indirect (and a few direct) ways to detect them, each with its own strengths and blind spots. Transit

Astronomy

Astronomy · L3 · Exoplanet Detection

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Note~235 words · 1 min

Light Is More Than What We See Visible light is only a narrow slice of the full electromagnetic spectrum. Every band, from long-wavelength radio waves to extremely short-wavelength gamma rays, carries different information about the Univers

Astronomy

Astronomy · L3 · The EM Spectrum in Astronomy

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Note~230 words · 1 min

Light Carries a Chemical Fingerprint Every element absorbs and emits light only at specific wavelengths, set by the fixed energy levels its electrons can occupy. That gives every element a unique pattern of spectral lines — a fingerprint th

Astronomy

Astronomy · L3 · Spectroscopy & Redshift

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Note~321 words · 2 min

The Densest Objects in the Universe When a massive star's core collapses at the end of its life, what it becomes depends on exactly how much mass is left behind: a neutron star, or a black hole. Neutron Stars and Degenerate Matter A neutron

Astronomy

Astronomy · L3 · Black Holes & Neutron Stars

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Note~327 words · 2 min

Where Could Life Exist? The search for life beyond Earth starts with a simple question: where could liquid water exist on a planet's surface? That range of orbital distances around a star is called the habitable zone. A star's luminosity se

Astronomy

Astronomy · L3 · Habitable Zones & the Search for Life

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Note~292 words · 1 min

Measuring the Unreachable No ruler can be laid across space, so astronomers measure distance with a ladder of methods, each rung calibrated by the one below it and each capable of reaching farther than the last. Rung One: Parallax As Earth

Astronomy

Astronomy · L3 · The Cosmic Distance Ladder

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Note~240 words · 1 min

A Magnetic Shield in a Charged Wind The Sun constantly sheds the solar wind — a stream of protons and electrons moving fast enough to escape its gravity. Earth's magnetic field deflects most of this wind around the planet, carving out a cav

Astronomy

Astronomy · L3 · Aurora & Magnetosphere Physics

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Note~273 words · 1 min

One Violent Afternoon, 4.5 Billion Years Ago Of the several competing ideas once proposed for how the Moon formed, one now dominates: not long after Earth itself formed, a Mars-sized protoplanet nicknamed Theia struck the young Earth at a g

Astronomy

Astronomy · L3 · Moon Formation & the Giant Impact

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Note~238 words · 1 min

A Natural Experiment in the Sky Individual stars are hard to date directly. Star clusters solve this problem: every star in a cluster formed from the same collapsing cloud, at essentially the same moment, with nearly the same starting compo

Astronomy

Astronomy · L3 · Star Clusters & Stellar Populations

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Note~271 words · 1 min

Messengers Bent by Magnetic Fields Cosmic rays are charged particles — overwhelmingly protons — arriving from space at speeds approaching that of light. Unlike photons, their paths are bent by every magnetic field they cross, so, except at

Astronomy

Astronomy · L3 · Cosmic Rays & High-Energy Astrophysics

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Note~235 words · 1 min

Mass Bends Light General relativity describes gravity not as a force acting at a distance but as the curvature of spacetime caused by mass and energy. Light travels along that curved spacetime, so its path visibly bends as it passes a massi

Astronomy

Astronomy · L3 · Gravitational Lensing

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Note~269 words · 1 min

From Impact to Crater When an asteroid strikes a planet's surface at tens of kilometres per second, its enormous kinetic energy, is dumped into the ground almost instantaneously, driving crater formation through three distinct stages. The C

Astronomy

Astronomy · L3 · Asteroid Impacts & Craters

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Note~287 words · 1 min

Five Ideas That Rewrote the Universe The history of astronomy is not a smooth accumulation of facts — it is a sequence of paradigm shifts, each one overturning the model that came before it once the evidence made the old picture untenable.

Astronomy

Astronomy · L3 · History of Astronomy: Paradigm Shifts

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Note~416 words · 2 min

One Data Point Is Not a Trend Until 1995, the only planetary system available to study was our own — eight planets on nearly circular orbits, rocky worlds close to the Sun and gas giants far out, with a wide, empty gap between them. Theorie

Astronomy

Astronomy · L3 · Exosolar System Architecture

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Note~337 words · 2 min

From Cloud Core to Spinning Disk The nebular hypothesis explains the Sun and planets as a single collapsing rotating cloud of gas and dust — a fragment of a larger molecular cloud, disturbed into collapse perhaps by a nearby supernova shock

Astronomy

Astronomy · L3 · Solar System Formation: The Nebular Hypothesis

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