Cosmic Evidence Investigator

Question the universe

Investigation path

Learning support

Guided mode Recommended for a first astronomy investigation

Progress

Begin by measuring the spectrum of the first galaxy.

NGSS focus

HS-ESS1-2

Construct an explanation of the Big Bang theory using astronomical evidence from light spectra, galaxy motion, matter composition, and cosmic background radiation.

What to notice: Each galaxy shows the same pattern of hydrogen lines, but the entire pattern may be shifted. Match the movable reference lines to the observed dark lines.

Virtual spectroscope

Hydrogen absorption spectrum

Target

Redshift estimate, z 0.0000

Move the cyan reference lines until they overlap the observed dark lines.

Pattern in the data

Distance and recession velocity

Measured0 / 6

TrendCollect at least 3 points

Estimated slope—

Model the pattern

Expansion from different observers

Observer

Scale of space1.00×

Important distinction

The galaxies are not shown growing larger. The grid spacing grows, representing increasing distance between galaxies. Switching observers shows that Earth is not a special center.

What to notice: The signal is nearly the same temperature in every direction. Tiny differences are shown with exaggerated colors so the pattern is visible.

Microwave receiver

Scan the sky

Average signal—

Telescope direction0°

Scan at least eight different directions.

Recorded evidence

Sky-direction measurements

Directions0 / 12

Direction	Temperature	Difference from mean
No measurements recorded.

Which pattern best describes the completed scan?

Complete enough scans, then describe the pattern.

What to notice: These are simplified mass measurements from widely separated, low-metallicity stars and interstellar gas. Compare whether the samples share a similar hydrogen-helium ratio.

Composition analyzer

Analyze low-metallicity gas

Analyzed0 / 4

Select a cloud to analyze its composition.

Compare samples

Composition records

Sample	Hydrogen	Helium	Trace
Analyze a cloud to begin.

What is the strongest pattern?

Analyze all four samples, then identify the shared pattern.

Competing explanations

Which model accounts for the evidence?

Use independent evidence

Select supporting observations

Galaxy redshift patternMore distant galaxies generally recede faster. Microwave backgroundA nearly uniform 2.7 K signal appears across the sky. Hydrogen-helium abundanceWidely separated samples share a similar primordial ratio. No special observerExpansion appears from multiple galaxy viewpoints.

Construct an explanation

Evidence-based reasoning

Explain how at least three observations support your selected model.

Complete the evidence sections before submitting your explanation.

Critique the model

What this simulation simplifies

Galaxy data: Classroom values follow a clean trend with modest noise. Real surveys contain many more objects, uncertainties, and local motions.

CMB map: Temperature differences are greatly exaggerated in color. The real variations are tiny compared with the approximately 2.7 K background.

Composition: The model uses rounded mass percentages from simplified low-metallicity samples. It does not directly sample the early universe or simulate nuclear reactions during the first minutes of cosmic history.

Expansion: A two-dimensional grid represents a three-dimensional universe and does not show gravity, dark matter, or dark energy.

Automatic record

Evidence notebook

1. Galaxy motion

Galaxies measured0

Farthest velocity—

No redshift measurements yet.

2. Microwave sky

Directions scanned0

Mean temperature—

No sky pattern recorded yet.

3. Composition

Clouds analyzed0

Mean H / He—

No composition pattern recorded yet.

Vocabulary in context

Spectrum: Light separated by wavelength.
Redshift: A shift toward longer wavelengths.
Recession velocity: How quickly distance is increasing in this model.
CMB: Ancient microwave light from the early universe.
Abundance: The proportion of matter in each element.