The 42nd Period | STEM Education Hub

🎯 Your Galaxy

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Use your galaxy's data only, and the constants in the box above.
Assume nearly all the galaxy's visible matter lies inside the edge of the bright disk.
Show every calculation — formula, numbers substituted, answer with units.
Your report is one to two pages, plus your annotated rotation curve.
No AI-generated writing. The point of this problem is building your own argument.
Due at the end of Day 3.

Redshift, recession velocity, and distance — z, then v, then d in megaparsecs and millions of light-years, with work shown.
An annotated rotation curve — mark the edge of the bright disk, the measured outer speed, and the speed visible matter predicts there.
The expected outer speed at your outermost measurement, from visible matter alone, compared with what was measured.
The missing mass — how many times the visible mass is really there, and what percent of it is dark matter.
Your argument — why dark matter is the best explanation, supported by your numbers and at least two independent lines of evidence from beyond this galaxy.
An alternative you took on — for example hidden ordinary matter, a measurement error, or modified gravity — and why the evidence points away from it.
One assumption you made, and how it could affect your answer.

A starting point — adjust weights to fit your class before assigning.

Category	Weight	Exemplary	Proficient	Developing	Incomplete
Redshift, Velocity & Distance	25 pts	Correct z, recession velocity, and distance (in Mpc and millions of light-years), with every step and formula shown.	Method correct; one arithmetic slip or a missing unit.	A formula misused or a step skipped, leading to a wrong distance.	Calculation missing.
Rotation-Curve Analysis	25 pts	Correctly describes the curve, calculates the expected outer speed from visible matter, and finds the mass ratio and dark-matter share — on an annotated graph.	Analysis mostly correct; graph annotations thin or one value off.	Describes the curve but doesn't quantify the missing mass.	No rotation-curve analysis.
Dark Matter Argument	25 pts	A clear claim backed by the student's own numbers plus at least two independent lines of evidence, explained in their own words.	Solid claim and data; outside evidence mentioned but not explained.	Asserts dark matter without connecting it to the data.	No argument.
Alternatives & Assumptions	15 pts	Takes on a real alternative (e.g. hidden ordinary matter, measurement error, modified gravity) and explains why the evidence favors dark matter; states at least one assumption made.	Names an alternative with thin reasoning.	No real alternative or assumption discussed.	Missing.
Communication	10 pts	Organized like a real analysis report: clear sections, labeled graph, correct units.	Mostly clear with minor gaps.	Hard to follow.	Not submitted.

🔭 Problem 5.3.1 · Unit 5 of 6 · Single Semester