Module 1: Observing the Sky & Solar System
Weeks 1–6 | Building your astronomical toolkit
Why this module matters
Before we can understand stars, galaxies, or the universe itself, we need a shared language. This module builds that language: navigating the sky, understanding how gravity shapes orbits, and learning how light carries information across cosmic distances.
Everything in this course rests on the tools you’ll master here. By the end of this module, you’ll understand how astronomers locate objects, predict motions, and decode the messages hidden in starlight.
Learning objectives
By the end of this module, you will be able to:
- Navigate the celestial sphere and locate objects using coordinates
- Explain the causes of Moon phases and eclipses
- Apply Kepler’s laws to describe orbital motion
- Describe how light and the electromagnetic spectrum reveal information about distant objects
- Explain how telescopes collect and analyze light
Lecture Readings
Spoiler Alerts — The Universe Is Weird
January 20, 2026A trailer for the semester: how astronomers turn photons into physical claims.
Lecture 1 Solutions: Spoiler Alerts
January 20, 2026Solutions to the Lecture 1 practice problems.
Tools of the Trade: Math Survival Kit
January 23, 2026Four problem-solving tools that let you navigate cosmic scales without drowning in zeros.
Lecture 2 Solutions: Math Survival Kit
January 23, 2026Solutions to the Lecture 2 practice problems.
Lecture 3 Solutions: The Sky Is a Map
January 26, 2026Solutions to the Lecture 3 practice problems.
The Sky Is a Map
January 26, 2026Celestial sphere geometry, seasons (tilt not distance), and angular size — how to navigate a sky made of angles.
Moon Geometry
January 28, 2026Moon phases and eclipses as geometry: illumination, viewing angle, nodes, and why eclipses don’t happen monthly.
Lecture 4 Solutions: Moon Geometry
January 28, 2026Solutions to the Lecture 4 practice problems.
From Ancient Skies to Kepler’s Laws
February 2, 2026How 2,000 years of astronomical puzzles led to Kepler’s three laws — patterns that describe planetary motion with unprecedented precision.
Lecture 5 Solutions: Kepler’s Laws
February 2, 2026Solutions to the Lecture 5 practice problems.
Newton’s Revolution — From Patterns to Physics
February 4, 2026Newton unified heaven and Earth: the same gravity that drops apples also guides planets. His laws transform Kepler’s patterns into physics — and give astronomers the power to weigh the universe.
The Cosmic Messenger — Light Carries Information
February 9, 2026You’ve never touched a star, yet you know what it’s made of. Light is how the universe talks to us — its wavelength encodes temperature, composition, motion, and more.
Reading the Glow — Temperature Written in Light
February 11, 2026Everything with temperature glows. Hotter objects glow bluer and brighter. By analyzing the spectrum of light, astronomers can read an object’s temperature from billions of kilometers away.
Decoding Starlight — Spectral Lines and Chemical Fingerprints
February 18, 2026Spectral lines are chemical fingerprints. Each element absorbs and emits light at unique wavelengths. By understanding the quantum origin of these lines, we can determine the composition of any star in the universe — without ever touching it.
Motion Revealed — Doppler Effect and the Astronomer’s Toolkit
February 20, 2026Spectral lines shift when objects move. The Doppler effect reveals velocities — from exoplanets to dark matter. Telescopes collect this light so we can decode it. This completes the astronomer’s toolkit for Module 2.
Our Cosmic Backyard — Solar System Architecture & Formation
February 23, 2026The solar system is where we apply everything we’ve learned. Kepler’s Laws give us distances. Newton’s gravity gives us masses. Blackbody radiation gives us temperatures. Spectroscopy gives us compositions. This lecture tours our cosmic neighborhood and explains how it formed.
Planetary Climates & Finding Other Worlds
February 25, 2026Venus is a hellscape. Mars is a frozen desert. Earth is just right. Why? The greenhouse effect — the same physics that determines planetary habitability is reshaping Earth’s climate today. Then we learn to find planets around other stars, building toward the biggest question: Are we alone?
Module 1 Synthesis — Are We Alone?
February 27, 2026You voted this your favorite NASA science question. Now let’s take it seriously — not as philosophy, but as astronomy. The Drake Equation provides a framework, the numbers are staggering, and stellar evolution explains why life-friendly rocky worlds were unlikely early on until the universe was enriched with heavy elements. This lecture synthesizes Module 1 and previews Module 2.
Solutions
Solutions are posted for Lectures 1–5 practice problems. Homework uses a subset of these, and additional solution sets will be posted as we go.
Lecture Slides
Spoiler Alert: The Universe Is Weird
January 20, 2026A trailer for the semester: how astronomers turn photons into physical claims.
Lecture 2: Tools of the Trade
January 23, 2026ASTR 101 math essentials: scientific notation, SI prefixes, units & conversions, ratio method, and rate problems — framed through cosmic scales.
The Sky Is a Map
January 26, 2026Celestial sphere geometry, seasons (tilt not distance), and angular size — how to navigate a sky made of angles.
Moon Geometry
January 28, 2026Moon phases and eclipses as geometry: illumination, viewing angle, orbital tilt, nodes, and why eclipses don’t happen monthly.
From Ancient Skies to Kepler’s Laws
February 2, 2026How retrograde motion puzzled ancient astronomers, and how Kepler’s three laws finally cracked the code of planetary motion.
Newton’s Revolution
February 4, 2026Newton unified heaven and Earth: the same gravity that drops apples also guides planets. His laws transform Kepler’s patterns into physics — and give astronomers the power to weigh the universe.
The Cosmic Messenger
February 9, 2026You’ve never touched a star, yet you know what it’s made of. Light is how the universe talks to us.
Reading the Glow
February 11, 2026Everything glows. Hotter objects glow bluer and brighter. By analyzing the spectrum, astronomers can read temperature from billions of kilometers away.
Decoding Starlight
February 18, 2026Spectral lines are chemical fingerprints. Each element has unique wavelengths. Quantum mechanics explains why.
Optional Reference (OpenStax Astronomy 2e)
Lecture readings are provided on this website. For additional depth, see the free OpenStax Astronomy 2e:
- Chapters 1–2: Science and the Universe; Observing the Sky
- Chapters 3–4: Orbits and Gravity; Earth, Moon, and Sky
- Chapters 5–6: Light and Matter; Telescopes
- What is dark energy? It makes up ~68% of the universe and drives accelerating expansion, but we don’t know what it actually is.
- Why does gravity exist? We can describe it (Newton, Einstein), but we don’t know why mass curves spacetime.
- Is the speed of light truly constant? Some theories suggest it may have varied in the early universe.