Empirical Earth · The Sky — Sun, Moon & Stars

Timing the Sun — coronal mass ejections and the real Earth–Sun distance

The claim

“The Sun is small and local; the '150 million km' is just an assumption.”

What is true

The Sun does look small enough to cover with a thumbnail, and nothing about looking at it tells you how far away it is.

What is measured

Solar storms take ~1–3 days to cross from the Sun at known speeds, placing it ~150 million km away, not a few thousand.

What would show this is wrong

a coronal-mass-ejection transit time inconsistent with a Sun ~150 million km away.

Sources

  1. Parker Solar Probe. Launched 2018; on 24 Dec 2024 it flew 3.8 million miles (6.1 million km) from the Sun's surface at ~430,000 mph — the fastest human-made object — relaying telemetry to AP link
  2. Coronal mass ejections & space weather. CMEs are imaged leaving the Sun (e.g. SOHO/LASCO at L1) at 300–3,000 km/s; forecasters time their arrival at Earth (typically 1–3 days; the 1859 Carri link
  3. Light-travel time across one astronomical unit. One AU is defined as 149,597,870,700 m = 499 light-seconds (~8 min 20 s), and is known to about one part in a billion from radar ranging of th link
  4. Tracking CMEs in three dimensions with STEREO. The twin STEREO spacecraft image coronal mass ejections from two viewpoints along Earth’s orbit and triangulate their progress across interplan link
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