Artist’s logarithmic scale conception of the observable universe. The Solar System gives way to the Milky Way, which gives way to nearby galaxies which then give way to the large-scale structure and the hot, dense plasma of the Big Bang at the outskirts. Each line-of-sight that we can observe contains all of these epochs, but the quest for the most distant observed object will not be complete until we’ve mapped out the entire Universe. (Credit: Pablo Carlos Budassi)
Our tiny home world, seemingly massive, is merely 12,742 km (7,917 miles) across.
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)
We typically think linearly: where the Sun is ~10,000 times farther away than Earth’s diameter.
The orbits of the planets in the inner Solar System aren’t exactly circular, but they are quite close, with Mercury and Mars having the biggest departures and the greatest ellipticities. If you were to draw an imaginary line connecting Earth-to-Mercury, you’d see Mercury’s apparent position migrate from west-to-east during most times, but during retrograde motion, when it overtakes the Earth, its position would instead migrate from east-to-west: a phenomenon that only an inner planet can experience. (Credit: NASA/JPL)
But cosmically, logarithmic scales — where each multiplicative factor of “10” defines another mark on our cosmic ruler — serve us far better.
The Earth, at nearly 13,000 kilometers (8,000 miles) in diameter, is tiny compared to the cosmic distances between the Earth-and-Moon or, more spectacularly, the Earth-and-Sun. But a logarithmic scale gives us a vastly different perspective, enabling us to reckon with disparate distance scales in a single visual image. (Credit: Pablo Carlos Budassi)
On a logarithmic scale, the Sun, Mercury, and Mars are practically equidistant.
The inner Solar System, including the planets, asteroids, gas giants, Kuiper belt, and more, is minuscule in scale when compared to the extent of the Oort Cloud. Sedna, the only large object with a very distant aphelion, may be part of the innermost portion of the inner Oort Cloud, but even that is disputed. On a linear scale, depicting the entire Solar System in a single image is incredibly limiting. (Credit: NASA/JPL-Caltech/R. Hurt)
Another factor of ~10,000 in distance takes us to the Oort cloud.
In the Solar System, we typically measure distances in Astronomical Units (AU), where the Earth-Sun distance is 1 AU. Mercury and Mars are also about ~1 AU from Earth, with Saturn at ~10 AU, the Kuiper belt ending before ~100 AU, and the Oort cloud largely existing at ~10,000 AU. It’s an enormous distance on a linear scale, but only a small set of “factors of 10” away on a logarithmic one. (Credit: Pablo Carlos Budassi)
A short logarithmic jump takes us from the Solar System to the stars.
This long-exposure image captures a number of bright stars, star-forming regions, and the plane of the Milky Way above the southern hemisphere’s ALMA observatory. The nearest stars are only a few light-years away: less than a factor of 10 from the edge of the Oort cloud. But more distant stars and features, still visible with the naked human eye, can be tens of thousands of light-years away instead. (Credit: ESO/B. Tafreshi (twanight.org))
Many of the brightest stars in Earth’s skies are under 1,000 light-years away.
Many of the brightest nearby stars to Earth are members of the Orion arm, which itself is a minor spur of the larger, grander Perseus arm of the Milky Way. From the nearest stars, a few light-years away, to these arms, a few thousands of light-years away, represents only three factors of “10” on a logarithmic scale. (Credit: Pablo Carlos Budassi)
Another small logarithmic jump brings us to our nearest spiral arms.
Gaia’s all-sky view of our Milky Way Galaxy and neighboring galaxies. The maps show the total brightness and color of stars (top), the total density of stars (middle), and the interstellar dust that fills the Galaxy (bottom). Note how, on average, there are approximately ~10 million stars in each square degree, but that some regions, like the galactic plane or the galactic center, have stellar densities well above the overall average. (Credit: ESA/Gaia/DPAC)
Beyond that lies the full Local Galactic Group.
The Perseus spiral arm leads into the full-scale Milky Way, with other galaxies in the Local Group lying only a single factor of “10” beyond the full-scale Milky Way. Another factor of 10 beyond that takes us to large galactic groups and even approaches the closest galaxy cluster. (Credit: Pablo Carlos Budassi)
Rapidly, neighboring galaxies become ubiquitous.
Our local supercluster, Laniakea, contains the Milky Way, our local group, the Virgo cluster, and many smaller groups and clusters on the outskirts, including the M81 Group. However, each group and cluster is bound only to itself and will be driven apart from the others due to dark energy and our expanding Universe. After 100 billion years, even the nearest galaxy beyond our own local group will be approximately a billion light-years away, making it many thousands, and potentially millions of times fainter than the nearest galaxies appear today. (Credit: Andrew Z. Colvin/Wikimedia Commons)
There are only a few factors of “10” in logarithmic distance that separate the nearest galaxies, located a few hundred thousand to a few million light-years away, to large-scale clustering features on the scales of hundreds of millions or possibly one billion light-years. At these scales, the Universe’s largest bound features begin to come into view. (Credit: Pablo Carlos Budassi)
Eventually the largest structures of all are revealed: the great cosmic web.
The growth of the cosmic web and the large-scale structure in the Universe, shown here with the expansion itself scaled out, results in the Universe becoming more clustered and clumpier as time goes on. Initially small density fluctuations will grow to form a cosmic web with great voids separating them, but what appear to be the largest wall-like and supercluster-like structures may not be true, bound structures after all, as late-time dark energy drives them apart. (Credit: Volker Springel/MPE)
Many of these features are only apparent: dark energy will tear these pseudostructures apart.
The largest features seen here, like “great walls” and “large quasar groups” may not be cosmologically bound structures, but rather apparent pseudostructures, where gravitation due to their cumulative masses will be insufficient to keep them bound. Dark energy, on the largest cosmic scales, will drive all things apart. (Credit: Pablo Carlos Budassi)
At the cosmic limits, the edges of time are revealed: the earliest moments after the hot Big Bang.
Our deepest galaxy surveys can reveal objects tens of billions of light years away, but even with ideal technology, there will be a large distance gap between the farthest galaxy and the Big Bang. At some point, our instrumentation simply cannot reveal them all, and the gap between the emission of the cosmic microwave background and the formation of the very first stars will finally be definitively revealed to us. (Credit: Sloan Digital Sky Survey)
This vertically oriented logarithmic map of the Universe spans nearly 20 orders of magnitude, taking us from planet Earth to the edge of the visible Universe. Each large “mark” on the right side’s scale bar corresponds to an increase in distance scales by a factor of 10. (Credit: Pablo Carlos Budassi)
