ASTR 101 — Homework #1 (Lectures 1–3)
Homework builds quantitative fluency and model-based reasoning. Expect multi-step problems and conceptual questions where units, assumptions, and physical interpretation matter as much as the final number. The purpose of homework is exam preparation and skill-building through consistent, high-quality practice — not busy work.
Submission workflow (two-stage)
Homework Solutions — due Monday 11:59 pm PT (Canvas)
- Must be uploaded as one single, readable PDF (not a photo dump).
- Organize clearly. Show your work. Label final answers.
- No late submissions. Instructor solutions will be posted Tuesday morning, so late work cannot be accepted.
- Lowest homework score will be dropped (to cover one off-week or emergency).
Self-Assessment + Reflection (“Grade Memo”) — due Wednesday 11:59 pm PT (Canvas)
- Self-assess (self-grade) your work using the homework rubric (posted on Canvas) and the posted solutions/guidance.
- Submit a brief grade memo that includes:
- what you got right (and why),
- what broke (and where),
- what you learned,
- what you will do differently next time.
- Your grade memo must also include:
- a per-problem self-rating (1–5) with brief justification, and
- AI and collaboration disclosure (even if “none”).
- Vague memos (e.g., “I need to study more”) will not earn full credit unless they include a specific error diagnosis and a concrete next-step habit.
How your homework is graded (Instructor 0–5 score)
I evaluate your combined submission (Monday solutions + Wednesday grade memo) and assign an overall score from 0–5. Homework is graded primarily on completion, professionalism, and learning behaviors, not just final correctness. “Professionalism” here means your work is readable, logically organized, shows steps and units, and reflects honest effort. Your grade memo is graded on the quality of your self-assessment, reflection, and evidence of growth.
Allowed (study support):
- Clarifying your own notes or assigned readings
- Generating practice questions (not answers to assigned problems)
- Explaining concepts at a different level for studying
Not allowed (graded work):
- Generating or rewriting homework solutions, derivations, or explanations you submit
- Submitting AI-generated reasoning you cannot reproduce on your own
Always disclose AI use in your grade memos, even if the use was allowed.
Topics: scientific thinking in astronomy • cosmic scales • units & scientific notation • “the sky is a map” • seasons misconceptions
Estimated time: ~3-4 hours
Why this homework exists (read this)
This is not busy work. Astronomy is a “reasoning from evidence” science, and the exams will ask you to explain and apply ideas — not just recall definitions.
This assignment is designed to:
- make the big ideas from Lectures 1–3 stick,
- give you repeated practice with the math tools you’ll use all semester,
- and help you build the habit of showing your reasoning (how you’ll earn points on exams).
What to do
Complete the assigned Practice Problems from the end of the following lecture readings:
Lecture 1: Spoiler Alerts — Practice Problems
Lecture 2: Foundations / Tools of the Trade — Practice Problems
Lecture 3: The Sky Is a Map — Practice Problems
Use the lecture pages for the full problem statements (located at the end of each lecture).
Problems to complete
Lecture 1
1, 2, 4, 6, 8
Lecture 2
1, 2, 3, 4, 6, 7, 12, 14
Lecture 3
2, 3, 7, 8, 11, 12
How to earn full credit
1) Show your work (always)
For any problem with numbers, your solution must include:
- setup (what you’re solving for)
- knowns/unknowns (what you’re given)
- equations or reasoning path (why you’re doing what you’re doing)
- units at every step (units are not decoration — they’re error-checking)
- a final answer that is clearly labeled (box/circle it)
If you only write a final number, you should expect major point loss even if it’s correct.
2) Explain your reasoning (conceptual problems)
For conceptual questions, write in complete sentences. Aim for:
- Claim: your answer
- Evidence/Reasoning: why (use the lecture ideas)
- Optional sketch: a quick diagram is often worth 10 sentences
3) Use diagrams like a scientist
For geometry/sky problems: draw a labeled sketch (Sun–Earth–observer, horizon/zenith, tilt, angles). You don’t need to be an artist — just be clear.
Collaboration and resources
- You may discuss ideas with classmates, but your write-up must be your own.
- If you worked with someone, add a short line at the top of your solution PDF: “Collaborators: …”
- You may use your notes, the readings, and a calculator.
Pro tips (to save time and pain)
Start with the conceptual questions first, then do the calculations.
When stuck, ask: “What is observable here? What is inferred?”
Use units as your lie detector.
Do a quick sanity check: is the answer the right order of magnitude?
Help
If you get stuck, bring at least one specific attempt (a diagram, your setup, where you got lost) to office hours. Struggle is normal; productive struggle is the point.