ASTR 101: Principles of Astronomy
Spring 2026
Welcome to ASTR 101
Explore the universe — from planets and stars to galaxies and the Big Bang. ASTR 101 is an introductory astronomy course that satisfies the SDSU General Education requirement in Natural Sciences / Physical Science (Area 5A).
This course goes beyond a “tour of the cosmos.” You’ll learn how astronomers know what they know: how we measure distances across space, decode the messages hidden in starlight, and piece together the life cycles of stars. Along the way, you’ll develop quantitative reasoning skills — working with data, units, and scientific arguments — that apply far beyond astronomy.
No prior physics or astronomy background is required, just curiosity and a willingness to engage with numbers and scientific thinking.
Course Modules
Module 1: Observing the Sky & Solar System
Weeks 1–6
How do we navigate the night sky? Why do the Moon’s phases change? What keeps planets in orbit? This module builds your astronomical toolkit: celestial coordinates, gravity and orbits, and how telescopes and light reveal the universe.
Module 2: Stars & Stellar Evolution
Weeks 7–13
Stars are not eternal — they are born, live, and die. Learn how the Sun generates energy through nuclear fusion, how we measure stellar distances and properties, and how stars evolve from formation to their final fates.
Module 3: Galaxies & Cosmology
Weeks 14–16
Zoom out to the largest scales: our Milky Way, billions of other galaxies, and the universe as a whole. Explore evidence for dark matter, the expanding universe, and the Big Bang — cosmic origins written in light.
How to Succeed
- Stay current. Complete readings before lecture and homework by the deadline.
- Engage in class. Bring your iClicker, participate in Friday activities, and ask questions.
- Use your resources. Office hours, the discussion board, and the Astronomy Help Room are there for you.
- Office hours: Fridays 11:00 am–1:00 pm (and by appointment) in Physics 239
- Canvas discussion: Post questions others might share
- SDSU Astronomy Help Room: Free tutoring (schedule on Canvas)