The speed of light and astronomical distances

It makes the conversion between space and time as these are but measurements of lengths in different directions in the same 4-dimensional geometrical space called "space-time".
As we observe astronomic objects by their light, we see them as they were when their light was emitted, thus with a delay that we commonly use to express their distances: 1 light-second = the distance crossed by light in 1 second ; 1 light-year = the distance crossed in 1 year, and so on. This can have importance : Ole Rømer first demonstrated in 1676 that light travelled at a finite speed by studying the apparent motion of Jupiter's moon Io.

Length of the Earth's equator
40,075 km 0.134 s
Geostationary orbit radius
35 786 km 0.119 s
Jupiter's mean radius
69,911 km
0.233 s
Proxima Centauri's radius (the nearest star, a red dwarf invisible to the naked eye)
98,000 km 0.327 s
Moon's semi-major axis (mean distance to Earth's center) 384 400 km 1.3 s
Io's semi-major axis (nearest Jupiter's big satellite)
421,700 km
1.41 s
Sun's radius 696 342 km 2.32 s
Sirius's radius
1,191,000 km
3.97 s
Callisto's semi-major axis (furthest Jupiter's big satellite)
1,882,700 km 6.28 s
Radius of the galactic black hole
27,000,000 km
90 s
149,598,261 km 8min 19s
Antares's radius
615,000,000 km
34.2 min
778,547,200 km 43 min
4,503,443,661 km 4h 10min
Average distance between neighboring stars in the center of the Omega Centauri globular cluster

1 month
Distance between Proxima Centauri and Alpha Centauri

4 months
Closest approach of Gliese 710 to the Sun after 1.4 million years from now (but now at 63.8 light-years)
1 year
Distance to Alpha Centauri (nearest visible star)

4.37 yr
Distance to Sirius (brightest star in appearance and second nearest visible star)

8.6 yr
Size of Omega Centauri (the biggest globular cluster of our galaxy)
86 yr
Width of the galactic disk

≈1500 yr
Distance to Omega Centauri

16,000 yr
Distance to the galactic center

28,000 yr
Diameter of our galaxy

100 k yr
Distance to the Large Magellanic Cloud (the main satellite of the Milky Way)

160 k yr
Distance between Andromeda and Triangulum (M33) galaxies

750 k yr
Distance to the Andromeda Galaxy (the main member of our Local group of galaxies, followed by our Milky Way and Triangulum)

2 M yr
Distance to NGC 55, the next significant galaxy outside the Local Group

7 M yr
Distance to the Virgo Galaxy Cluster (the biggest nearby galaxy cluster, at the heart of the Virgo supercluster we belong to)

50 M yr

The speed of light has physical effects in the following contexts:

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The energy of nuclear reactions + The radius of nuclei

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