← Back to the archive★ Support my pages
DD-546SpaceFiled Last updated

Universal Sizing

Short answer: The observable universe spans about 93 billion light-years. Its oldest light has traveled about 13.8 billion years, but expansion has carried those regions much farther away since.

The Milky Way is about 100,000 light-years wide with an estimated 100 to 400 billion stars, and the observable universe holds hundreds of billions to perhaps 2 trillion galaxies. The footage, credited to explainingtheuniverse, shows a zoom out through space.

VideoWrite-up1 sources
More like this★ Support my pagesCite this file

What should you know about Universal Sizing?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. About 93 billion ly.

    DD-546-F01 · Write-up · Exhibit A (Diameter)

  2. 13.8 billion years.

    DD-546-F02 · Write-up · Exhibit B (Age of light)

Video transcript: Universal Sizing: The Observable Universe Is About 93 Billion Light-Years Across

Did you know, the universe is incomprehensibly vast, with the observable portion stretching about 93 billion light years across, meaning light from the farthest regions has taken over 13.8 billion years to reach us, but due to the universe's expansion, those regions are now much farther away. Our galaxy, the Milky Way, is about 100,000 light years wide, and contains an estimated 100 to 400 billion stars, while the observable universe contains over 2 trillion galaxies, each with billions of stars and potentially even more planets. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 28.6s Reel ·

Video coming soonUniversal Sizing · Instagram Reel
Universal Sizing: The Observable Universe Is About 93 Billion Light-Years Across Instagram Reel · · 28.6s

The write-up

The observable universe is about 93 billion light-years across. Light from its edge left 13.8 billion years ago.

  1. Exhibit A

    Diameter

    About 93 billion ly.

  2. Exhibit B

    Age of light

    13.8 billion years.

  3. Exhibit C

    Milky Way

    About 100,000 ly.

  4. Exhibit D

    Stars

    100-400 billion.

  5. Exhibit E

    Galaxies

    Hundreds of billions to ~2 trillion.

Questions people ask about Universal Sizing

Diameter?

Expansion.

Source: Write-up · Exhibit A (Diameter) · Wikipedia: Observable universe

Milky Way width?

Disk.

Source: Write-up · Exhibit B (Age of light) · Wikipedia: Observable universe

Stars in Milky Way?

Estimate.

Source: Write-up · Exhibit C (Milky Way) · Wikipedia: Observable universe

Age of oldest light?

Big Bang.

Source: Write-up · Exhibit D (Stars) · Wikipedia: Observable universe

Why bigger than 13.8 billion ly?

Space stretches.

Source: Write-up · Exhibit E (Galaxies) · Wikipedia: Observable universe

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Diameter?

    1. About 93 billion ly
    2. 13.8 billion ly
    3. 1 million ly
    4. 100,000 ly
    Show the answer

    Answer: A. About 93 billion ly Expansion. Source: Write-up · Exhibit A (Diameter) · Wikipedia: Observable universe

  2. Milky Way width?

    1. About 100,000 ly
    2. 1 ly
    3. 1 billion ly
    4. 10 ly
    Show the answer

    Answer: A. About 100,000 ly Disk. Source: Write-up · Exhibit B (Age of light) · Wikipedia: Observable universe

  3. Stars in Milky Way?

    1. 100-400 billion
    2. 1 million
    3. 10
    4. 1 trillion trillion
    Show the answer

    Answer: A. 100-400 billion Estimate. Source: Write-up · Exhibit C (Milky Way) · Wikipedia: Observable universe

  4. Age of oldest light?

    1. 13.8 billion years
    2. 4.5 billion
    3. 1 million
    4. 100 years
    Show the answer

    Answer: A. 13.8 billion years Big Bang. Source: Write-up · Exhibit D (Stars) · Wikipedia: Observable universe

  5. Why bigger than 13.8 billion ly?

    1. Expansion
    2. Error
    3. Mirrors
    4. Black holes
    Show the answer

    Answer: A. Expansion Space stretches. Source: Write-up · Exhibit E (Galaxies) · Wikipedia: Observable universe

Cite this case file

Easterling, Marcus. "Universal Sizing." The Detail Department (DetailEnjoyer), case file DD-546, last updated Apr 17, 2025. https://detailenjoyer.com/case/universal-sizing/

Permalink: https://detailenjoyer.com/case/universal-sizing/ · Last updated

Markdown version

Cite a single fact by its ID, for example DD-546-F01 → https://detailenjoyer.com/case/universal-sizing/#DD-546-F01