When we look at a body in the sky, we receive light that left it some time ago. That time depends on the distance.
The question
When you look at the Sun, do you see it as it is right now?
What you do Send out the Sun’s light and watch it reach the planets one by one: the clock counts the journey time. Then choose a body, as far as Earendel: the further away it is, the older what you see.
Without JavaScript, here are the animation’s data.
| Quantity | Value | Source |
|---|---|---|
| Speed of light | 299,792,458 m/s | 1 |
| Astronomical unit (mean Earth–Sun distance) | 149,597,870,700 m | 2 |
| Planet | Mean distance from the Sun | Light travel time | Source |
|---|---|---|---|
| Mercury | 57.9 million km | 3 min 13 s (calculated) | 3 |
| Venus | 108.2 million km | 6 min 1 s (calculated) | 3 |
| The Earth | 149.6 million km | 8 min 19 s (calculated) | 3 |
| Mars | 228.0 million km | 12 min 41 s (calculated) | 3 |
| Jupiter | 778.5 million km | 43 min 17 s (calculated) | 3 |
| Saturn | 1,432.0 million km | 1 h 20 min (calculated) | 3 |
| Uranus | 2,867.0 million km | 2 h 39 min (calculated) | 3 |
| Neptune | 4,515.0 million km | 4 h 11 min (calculated) | 3 |
| Body | Distance | Light travel time | Source |
|---|---|---|---|
| The Sun | 1 astronomical unit | 8 min 19 s (calculated) | 2 |
| Neptune | 4,515 million km on average | 4 h 11 min (calculated) | 3 |
| Earendel | — | 12.9 billion years | 4 |
The travel times to the planets, and those for the Sun and Neptune, are calculated: distance divided by the speed of light. Earendel’s is given by the source. In the animation, the distances to the planets are on a logarithmic scale.
The takeaway Light takes time to travel. We see the Sun as it was eight minutes ago, and Earendel as it was 12.9 billion years ago.
Photo credits 10
- The Sun in visible light, photographed by NASA’s SDO satellite on 10 August 2024. NASA/SDO, AIA, EVE and HMI science teams, Public domain, source
- Neptune, from the last whole-planet images taken by Voyager 2 through green and orange filters (1989); the Great Dark Spot is visible. NASA, Public domain, source
- The star nicknamed Earendel (indicated by an arrow), in its host galaxy, which appears as a red smear; the whole scene is seen through the gravitational lens of a galaxy cluster lying between it and us (Hubble Space Telescope). NASA, ESA, B. Welch (JHU), D. Coe (STScI), A. Pagan (STScI), CC BY 4.0, source
- Mercury, a mosaic of images from NASA’s MESSENGER probe (2011). NASA/JHUAPL, Public domain, source
- Venus, wrapped in clouds, photographed by NASA’s Mariner 10 probe in February 1974. NASA/JPL-Caltech, Public domain, source
- The Earth photographed on 7 December 1972 by the Apollo 17 crew on their way to the Moon: Africa, Antarctica and the Arabian Peninsula are visible. NASA, Apollo 17 crew, Public domain, source
- Mars, a mosaic of 102 images from the Viking 1 orbiter (1980); in the centre, the Valles Marineris canyon. NASA / USGS (PIA04304), Public domain, source
- Jupiter photographed in full by the Hubble Space Telescope on 21 April 2014. NASA, ESA and A. Simon (Goddard), Public domain, source
- Saturn in natural colour, from images taken by the Cassini probe (2008). NASA / JPL / Space Science Institute, Public domain, source
- Uranus photographed by the Voyager 2 probe in 1986. NASA/JPL-Caltech, Public domain, source
.jpg){kind=link}
_ESA24011076.jpg){kind=link}
.jpg){kind=link}
Sources 4
Bureau international des poids et mesures, Le Système international d’unités (SI), 9ᵉ éd., 2019, section 2.3.1, p. 19.
Le mètre, symbole m, est l’unité de longueur du SI. Il est défini en prenant la valeur numérique fixée de la vitesse de la lumière dans le vide, c, égale à 299 792 458 lorsqu’elle est exprimée en m s−1, la seconde étant définie en fonction de ∆νCs. Cette définition implique la relation exacte c = 299 792 458 m s−1.
Editors’ translation The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum, c, to be 299 792 458 when expressed in the unit m s−1, where the second is defined in terms of ∆νCs. This definition implies the exact relation c = 299 792 458 m s−1.
Open access open the source · checked on 9 September 2026
Bureau international des poids et mesures, Le Système international d’unités, chapter 4, table 8 (non-SI units accepted for use with the SI), p. 33, and note (j), p. 34.
unité astronomique […] au […] 1 au = 149 597 870 700 m […] L’unité astronomique a été définie lors de la XXVIIIe Assemblée générale de l’Union astronomique internationale (Résolution B2, 2012).
Editors’ translation astronomical unit […] au […] 1 au = 149 597 870 700 m […] The astronomical unit was defined at the XXVIII General Assembly of the International Astronomical Union (Resolution B2, 2012).
Open access · checked on 24 October 2026
Williams, David R., “Planetary Fact Sheet – Metric”, NASA Goddard Space Flight Center (NSSDCA), updated 18 March 2025, rows “Diameter (km)” and “Distance from Sun (10^6 km)”, columns Mercury to Neptune.
Diameter (km) 4879 12,104 12,756 6792 142,984 120,536 51,118 49,528 […] Distance from Sun (10^6 km) 57.9 108.2 149.6 228.0 778.5 1432.0 2867.0 4515.0
Open access open the source · checked on 27 October 2026
ESA / Hubble, communiqué heic2203, “A Record Broken: Hubble Finds the Most Distant Star Ever Seen”, 30 March 2022, press release of 30 March 2022.
its light has taken 12.9 billion years to reach Earth, appearing to us as it did when the universe was only 7 percent of its current age, at redshift 6.2
Open access open the source · checked on 9 September 2026