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How Many Stars are in the Sky?

2020-01-31 · explainer · Hank · 3:56 · watch on YouTube

Topic: Science & nature · mode: Explainer · tags: timely hook

Marking the end of the Spitzer Space Telescope's mission, Hank answers his childhood question of how many stars are in the sky: counting the Milky Way's stars is impossible, so astronomers estimate 100 to 400 billion, and in 2020 we still don't know, though Spitzer's infrared map shows what hundreds of billions of stars look like.

What is said

The parts of the video and what is said in each (★ — how much it matters to the video).

00:00:00 — Hank's 'very bad image' and his childhood question: how many stars are in the sky, and why it depends on conditions and equipment

  • ★★ Hank says the seemingly very bad image he shows is objectively one of the best images ever taken in human history. (playful) — 00:00:00
  • ★★ Hank says as a kid he was frustrated that, though we knew the galaxy's size and our place in it, no one could tell him how many stars are in the sky. — 00:00:00
  • ★★ Hank says the number of visible stars depends on conditions and on equipment, and once equipment counts the question becomes how many stars are in the Milky Way. — 00:00:23

00:00:52 — Why the Milky Way's stars can't be counted: gas clouds, Spitzer's infrared map, star soup, and the 100 to 400 billion estimate

  • ★★★ Hank says the Milky Way's stars can't be counted: giant gas clouds hide huge sections of the galaxy, and more importantly there are just too many stars. — 00:00:52
  • ★★★ Hank says the image is two million photos taken over ten years by the Spitzer Space Telescope, which ended its mission this week (week of 27 January 2020). — 00:00:52
  • ★★ Hank says Spitzer is an infrared telescope that sees the heat of stars through the gas clouds, giving a less occluded view of the galactic core. — 00:01:20
  • ★★ Hank says even so not all stars are visible, because other stars are in the way: the view from the Sun's place at the Milky Way's edge looks through almost the whole galaxy. — 00:01:41
  • ★★ Hank says looking outward through the galaxy's thin band toward the intergalactic void gives a thinner soup of stars, but still a soup. — 00:02:10
  • ★★★ Hank says astronomers today estimate the Milky Way has between 100 and 400 billion stars, a range he finds huge. — 00:02:10
  • ★★★ Hank says since we can't count, the number is estimated from the galaxy's mass and the average star mass, both of which have significant wiggle room. — 00:02:39
  • ★★★ Hank tells his 1980s child self that in 2020 we still don't know how many stars are in the Milky Way. — 00:02:39

00:03:02 — We still don't know; thanks to the Spitzer team; Edwin Hubble and Lyman Spitzer

  • ★★ Hank says the image, decades of work, gives an idea of what hundreds of billions of stars look like, which is pretty cool. — 00:03:02
  • ★ Hank thanks everyone who worked on the Spitzer Space Telescope project; the galactic map was only one of its achievements. — 00:03:02
  • ★★ Hank says only a hundred years ago people argued whether the Milky Way was the entire universe; Edwin Hubble proved other galaxies exist. — 00:03:02
  • ★★ Hank says Lyman Spitzer first conceived of putting telescopes in space and was a huge champion of the Hubble Space Telescope. — 00:03:48

In the description and comments

  • ★★ The description says Spitzer carried liquid helium keeping it two degrees warmer than interstellar space; when it ran out its imaging degraded and the mission has now ended. — video description
  • ★★ The description says the image maps candidates for other telescopes, especially the infrared James Webb Space Telescope, which will launch, fingers crossed, in March 2021. (hedged) — video description
  • ★★ The description points viewers to a website where they can spend time with the image, one of the best pictures humanity has taken. — video description

Threads in this video

Where the stories that moved here went next

Mentioned

Central: Milky Way · Spitzer Space Telescope · star

Also: Edwin Hubble · Hubble Space Telescope · infrared astronomy · Sun (star)

Only in the description or credits: James Webb Space Telescope · Lyman Spitzer

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