Everything we see is a glimpse into the past.

From atop a high mountain, a distant high mountain several dozens of kilometers, even up to 100 kilometers distant, can be glimpsed on a clear day. At a distance of 100 kilometers, light takes about 33 microseconds to complete a one-way trip.

A distant mountaintop 100 kilometers away appears as it did 33 microseconds ago.

Although the Earth might be large and massive compared to the Moon, both bodies are very small compared to the distance between them. It takes about 1.25 seconds for light to travel one-way from the Earth to the Moon, and the Earth-Moon separation is about 30 times the Earth’s diameter. The Earth is also 80 times more massive than the Moon, but its surface gravity is only ~6 times as great.

The Moon’s more distant light arrives from ~1.25 seconds in the past.

Although the light from the Sun might appear to be a “right now” phenomenon, like the silhouettes of the shadows in the foreground, because of its great distance away, its now-arriving light was emitted about 8 minutes and 20 seconds ago.

We see the Sun, 150 million kilometers away, as it was ~8.3 minutes ago.

Pluto is the most distant world visited by a spacecraft created on Earth and is presently more than 5 billion kilometers distant. From Earth, light from Pluto arrives after a typical journey of just over 5 hours at present.

Pluto, at a distance of 5.5 billion kilometers, appears as it did just over 5 hours ago.

In the early 21st-century, we’ve successfully mapped out practically all the stars in our neighborhood in three-dimensional space. The closest stars to us don’t always align with the stars we can see, as what’s visible is determined by a combination of distance and intrinsic brightness, but all stars beyond the Sun are at a much, much greater distance than anything within our Solar System.

However, interstellar distances are far greater than interplanetary ones.

This photo showcases Proxima Centauri: the closest star to our own Sun at present. Although it’s only 4.24 light-years away, Proxima Centauri is not even close to visible to the naked eye, as it’s intrinsically nearly 1000 times fainter than the Sun.

Light from the nearest star, Proxima Centauri, arrives after journeying for 4.2 years.

This image shows Sirius A and B, a bluer and brighter star than our Sun and a white dwarf star, respectively, as imaged by the Hubble space telescope. Sirius A, the main star, is an A class star (as opposed to our Sun being a G class star): twice as massive as the Sun, some ~4000 K hotter than the Sun at its photosphere, and about 25 times as intrinsically luminous as our Sun. Sirius B once had about five times the Sun’s mass, but is now less massive, as a white dwarf, than its surviving stellar companion.

Sirius, the brightest star, appears as it did 8.6 years ago.

The constellation of Cassiopeia is familiar to casual skywatchers as a big “W” in the sky, but in truth the constellation contains many thousands of stars that are fainter and impossible to resolve without astronomical equipment. Although V762 Cas is often touted as the most distant naked-eye star, it’s only ~2500 light-years away: much less distant than visible hypergiant stars like V509 Cas.

The most distant naked-eye stars are hypergiants, like V509 Cassiopeiae: appearing as they did ~10,000 years ago.

This 1888 image of the Andromeda Galaxy, by Isaac Roberts, is the first astronomical photograph ever taken of another galaxy. It was taken without any photometric filters, and hence all the light of different wavelengths is summed together. Every star that’s part of the Andromeda galaxy has not moved by a perceptible amount since 1888, a remarkable demonstration of how far away other galaxies truly are. Although Andromeda is a naked-eye object under even modestly dark skies, it was not recorded until the year 964, and was not shown to be extragalactic until 1923.

But extragalactic objects are even farther away, with nearby Andromeda’s appearance reflecting its properties 2.5 million years ago.

Markarian’s chain, shown here, represents an alignment of large, massive galaxies found within the Virgo cluster. There are approximately 1,000 large galaxies in the Virgo cluster, a large fraction of which were discovered way back in the 18th century. The Virgo cluster is located some 50–60 million light-years away from our Milky Way and is the largest concentration of galaxies in the extremely nearby Universe, containing many giant ellipticals.

The Virgo cluster galaxies we see are 55-60 million years in the past.

This side-by-side view of galaxy cluster SMACS 0723 shows the MIRI (left) and NIRCam (right) views of this region from JWST. Note that although there’s a bright galaxy cluster at the center of the image, the most interesting objects are gravitationally lensed, distorted, and magnified by the cluster itself, and are located far more distant than the cluster itself.

JWST’s first science target, cluster SMACS 0723, appears as it was 4.6 billion years ago: when the Sun was first forming.

Shown within the context of the JWST JADES field, galaxy JADEs-GS-z14-0 is completely unremarkable, but nevertheless has just broken the cosmic distance record again, becoming the first galaxy ever found when the Universe was under 300 million years old: just 2.1% of its current age. From its vantage point within the expanding Universe, it would see our proto-Milky Way as it was some 13.52 billion years ago: when we were just 2.1% of our current age.

The light from our most distant observed galaxy, JADES-GS-z14-0, is 13.5 billion years old: ~98% of the Universe’s age.

COBE, the first CMB satellite, measured fluctuations to scales of 7º only. WMAP was able to measure resolutions down to 0.3° in five different frequency bands, with Planck measuring all the way down to just 5 arcminutes (0.07°) in nine different frequency bands in total. All of these space-based observatories detected the Cosmic Microwave Background, confirming it was not an atmospheric phenomenon, and that it had a cosmic origin.

Only the Big Bang’s leftover glow, from 13.8 billion years ago, appears older.

The extent of the visible Universe now goes on for 46.1 billion light-years: the distance that light emitted at the instant of the Big Bang would be located from us today, after a 13.8 billion year journey. As time marches on, light that’s even farther away, that is still on its way to us, will eventually arrive: from slightly greater distances and with slightly greater redshifts. We see into the past when we look out to great distances because the light emitted from distant objects must traverse those great intergalactic distances at a finite speed: the speed of light.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.