Quick take:

• Here on Earth, our entire planet is a little under 13,000 kilometers in diameter, or about seven orders of magnitude greater than the size of a single human being.
   

• But as we go up, to larger and larger scales, we find that stars, stellar systems, star clusters, galaxies, clusters of galaxies, and more show us how insignificant human, and even planetary, scales truly are.
   

• Even with all we know, the vast abyss of the unobservable Universe is larger than the cumulative suite of all we can see. These images show how big our Universe is on truly cosmic scales.

This image, taken from the International Space Station by astronaut Karen Nyberg in 2013, shows the two largest islands on the southern part of the Mascarene Plateau:

Réunion, in the foreground, and Mauritius, partially covered by clouds.

To see a human on Earth from the altitude of the ISS, a telescope the size of Hubble would be needed.

The scale of a human is less than 1/5,000,000 the scale of Earth, but Earth is just a proverbial drop in the cosmic ocean, with a diameter of only a little over 10,000 kilometers.

(Credit: NASA/Karen Nyberg)

This view of the Earth comes to us courtesy of NASA's MESSENGER spacecraft, which had to perform flybys of Earth and Venus in order to lose enough energy to reach its ultimate destination:

Mercury...

Several hundred images, taken with the wide-angle camera in MESSENGER's Mercury Dual Imaging System (MDIS), were sequenced into a movie documenting the view from MESSENGER as it departed Earth.

Earth, an oblate spheroid, rotates roughly once every 24 hours on its axis and moves through space in an elliptical orbit around our Sun.

(Credit: NASA/MESSENGER)

Of the eight planets in our Solar System, the four gas giant worlds are the least dense, with less than half the density of the least dense rocky planet (Mars), and with Saturn being even less dense than water.

(Credit: NASA/Lunar and Planetary Institute)

Brown dwarfs, between about 0.013–0.080 solar masses, will fuse protons+deuterons or deuterons+deuterons into helium-3 or tritium, remaining at the same approximate size as Jupiter but achieving much greater masses.

Red dwarfs are only slightly larger but do initiate proton-proton fusion, but even the Sun-like star shown here is not shown to scale here; it would have about 7 times the diameter of a low-mass star.

Stars can be up to nearly 2000 times the diameter of our Sun within this Universe.

(Credit: NASA/JPL-Caltech/UCB)

This illustration shows some of the largest stars in the Universe, along with the orbits of Saturn (brown ellipse) and Neptune (blue ellipse) for comparison.

The stars, from left to right, are the largest blue hypergiant, yellow hypergiant, orange hypergiant, and then the largest two stars of all: the red hypergiants UY Scuti and Stephenson 2–18.

The largest stars are approximately 2,000 times the diameter of our Sun, but the temperatures at the surfaces of these stars range from only a few thousand K all the way up to Wolf-Rayet stars, with temperatures of ~200,000 K.

(Credit: SkyFlubbler/Wikimedia Commons)

This diagram shows the relative sizes of the event horizons of the two supermassive black holes orbiting one another in the OJ 287 system.

The larger one, of ~18 billion solar masses, is 12 times the size of Neptune's orbit; the smaller, of 150 million solar masses, is about the size of the asteroid Ceres's orbit around the Sun.

The heaviest known black hole is only a few times more massive (and hence, a few times larger in radius) than OJ 287's primary.

(Credit: NASA/JPL-Caltech/R. Hurt (IPAC))

A logarithmic chart of distances, showing the planets, the Voyager spacecraft, the Oort Cloud, and our nearest star:

Proxima Centauri.

If we imagine building larger and larger particle accelerators, every factor of 10 in radius gets us another factor of 10 in energy, but typically at the expense of another factor of 100 in cost.

On planetary and stellar scales, this can get prohibitively large very quickly.

(Credit: NASA/JPL-Caltech)

An illustration of the inner and outer Oort cloud surrounding our Sun.

While the inner Oort cloud is torus-shaped, the outer Oort cloud is spherical.

The true extent of the outer Oort cloud may be under 1 light-year, or greater than 3 light-years; there is a tremendous uncertainty here.

Any massive object that passes through the Oort cloud has a significant chance of perturbing the objects within its vicinity.

(Credit: Pablo Carlos Budassi/Wikimedia Commons)

Within this dense star field, at left, a few candidate members of an individual structure, either a globular cluster remnant or a very low-mass dwarf galaxy, can be pulled out by sorting the stellar properties of the objects inside of it.

(Credit: CFHT / S. Gwyn / S. Smith)

The giant galaxy cluster, Abell 2029, houses galaxy IC 1101 at its core.

At 5.5-to-6.0 million light-years across, over 100 trillion stars and the mass of nearly a quadrillion suns, it's the largest known galaxy of all by many metrics.

A survey of the brightest galaxy within all of the Abell clusters reveals a cosmic motion that's inconsistent with the CMB dipole.

(Credit: Digitized Sky Survey 2; NASA)

Composite of galaxies from the smallest to the largest, shown (approximately) actual size.

The giant elliptical galaxy at the heart of cluster Abell 2029, IC 1101, is the largest known galaxy in the Universe, at least in terms of stellar extent.

It is much, much larger than the Milky Way or Andromeda (or any spiral galaxy), but also towers over even other typical giant ellipticals.

(Credit: E. Siegel)

This animation showcases Porphyrion, its extent, and many of the features observed in radio wavelengths with LOFAR and GMRT.

This is the largest black hole jet system, at present, ever discovered.

(Credit: Susanne Landis & Konrad Rappaport (Science Communication Lab))

The impressively huge galaxy cluster MACS J1149.5+223, whose light took over 5 billion years to reach us, is among the largest bound structures in all the Universe.

On larger scales, nearby galaxies, groups, and clusters may appear to be associated with it, but are being driven apart from this cluster due to dark energy.

Superclusters are only apparent structures, but the largest galaxy clusters that are bound can still reach hundreds of millions, and perhaps even a billion, light-years in extent.

(Credit: NASA, ESA, and S. Rodney (JHU) and the FrontierSN team; T. Treu (UCLA), P. Kelly (UC Berkeley), and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI))

The Sloan Great Wall is one of the largest apparent, though likely transient, structures in the Universe, at some 1.37 billion light-years across.

It may just be a chance alignment of multiple superclusters, but observations definitively indicate that it isn't a single, gravitationally bound structure, as dark energy is in the process of driving it apart.

The galaxies of the Sloan Great Wall are depicted at right.

(Credit: Willem Schaap (L); Pablo Carlos Budassi (R)/Wikimedia Commons)

The size of our visible Universe (yellow), along with the amount we can reach (magenta) if we left, today, on a journey at the speed of light.

The limit of the visible Universe is 46.1 billion light-years, as that's the limit of how far away an object that emitted light that would just be reaching us today would be after expanding away from us for 13.8 billion years.

Anything that occurs, right now, within a radius of 18 billion light-years of us, will eventually reach and affect us; anything beyond that point will not.

Each year, another ~20 million stars cross the threshold from being reachable to being unreachable.

(Credit: Andrew Z. Colvin and Frederic Michel, Wikimedia Commons; Annotations: E. Siegel)

This simulation (click above image) shows the large-scale structure of the Universe on the scales of the actual cosmic horizon: approximately 93 billion light-years across.

At this level, even the largest cosmic structures are reduced to mere blips, showcasing just how uniform, smooth, and equal the Universe is on the largest of cosmic scales.

(Credit: The Millennium Simulation, V. Springel et al.; Modifications: E. Siegel)

We can imagine a very large number of possible outcomes that could have resulted from the conditions our Universe was born with.

The fact that all 10⁹⁰ particles contained within our Universe unfolded with the interactions they experienced and the outcomes that they arrived at over the past 13.8 billion years led to all the intricacies of our experiences, including our very existence.

It is possible, if there were enough chances, that this could occur many times, leading to a scenario that we think of as "infinite parallel Universes" that contain all possible outcomes, including the roads our Universe didn't travel.

(Credit: MUSTAFABULENT / Adobe Stock)

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