Remember why we look up

The night sky, familiar to all of us, holds a sense of wonder unlike anything else.

The Milky Way, as seen at La Silla observatory, is a stunning, awe-inspiring sight to anyone, and offers a spectacular view of a great many stars in our galaxy. Although there are definitely regions, like towards our galactic center, that are denser in stars than others, the average “square degree” on the sky contains million 10 million stars from the Milky Way.

(Credit: ESO / Håkon Dahle)

For countless generations, we’ve gazed upon the heavenly abyss with awe.

The effects of light pollution on what a naked-eye observer can see in the night sky. The artificial light produced by objects on the ground can wash out the naturally occurring objects in the night sky, rendering many objects unable to be seen. Light pollution can wash out all but the brightest meteors during a meteor shower.

(Credit: Stellarium Labs)

Today, light pollution and satellite contamination have stolen those pristine views from many of us.

new satellites

This image of Venus and the Pleiades shows the tracks of Starlink satellites. The reflective surfaces of the satellites, coupled with the fact that they are orbiting around the Earth, mean that astronomical observations that require very long exposures capture “tracks” of the satellites in their images.

(Credit: T. Hansen / IAU OAE / Creative Commons Attribution)

Even so, each glimpse of what lies beyond Earth compels us to look farther.

Milky Way center

This spectacular composite image, which combines X-ray, infrared, and optical light from NASA’s great observatories, was our best view of what’s going on in the galactic center as of 2009. Over the past ~ 13 years, however, we’ve taken data that has revealed novel features that, at present, have yet to be fully explained.

(Credit: NASA / JPL-Caltech / ESA / CXC / STScI)

Out there, among the stars, galaxies, and beyond, lies the answers to the greatest mysteries of all.

m81 group

This multiwavelength view of the two largest, brightest galaxies in the M81 group shows stars, plasmas, and neutral hydrogen gas. The gas bridge connecting these two galaxies infalls onto both members, triggering the formation of new stars. Both galaxies are smaller and lower in mass than the Milky Way, but both house much more massive supermassive black holes than we do.

(Credit: R. Gendler, R. Croman, R. Colombari; Acknowledgment: R. Jay GaBany; VLA Data: E. de Block (ASTRON))

Each glittering point of light is its own stellar system, containing planets, moons, and possibly even life.

51 Eri b was discovered in 2014 by the Gemini Planet Imager. At 2 Jupiter masses, it is the coolest and lowest mass imaged exoplanet to date, and orbits only 12 Astronomical Units from its parent star. To image beings on the surface of this world would require a telescope with billions of times our present best resolution.

(Credit: Jason Wang (Caltech) / Gemini Planet Imager Exoplanet Survey)

We’ve seen individual planets forming, and may soon discover extrasolar biological activity.

A sample of 20 protoplanetary disks around young, infant stars, as measured by the Disk Substructures at High Angular Resolution Project: DSHARP. Observations such as these taught us that protoplanetary disks form primarily in a single plane, and tend to support the core accretion scenario of planet formation. The disk structures are seen in both infrared and millimeter / sub-millimeter wavelengths.

(Credit: SM Andrews et al., ApJL, 2018)

Within the Milky Way galaxy, alone, there are billions of potentially inhabited worlds.

5000 exoplanets

This diagram shows the discovery of the first 5000+ exoplanets we know of, and where they’re located on the sky. Circles show location and size of orbit, while their color indicates the detection method. Note that the clustering features are dependent on where we’ve been looking, not necessarily on where planets are preferentially found. Extrapolated over the stars in our galaxy, we expect the number of potentially inhabited worlds numbers in the billions.

(Credit: NASA / JPL-Caltech)

Even beyond that, there are anywhere from 6 to 20 trillion galaxies within the observable Universe.

how many galaxies

Various long-exposure campaigns, like the Hubble eXtreme Deep Field (XDF) shown here, have revealed thousands of galaxies in a volume of the Universe that represents a fraction of a millionth of the sky. This image contains 5,500 galaxies, but takes up just 1-32,000,000th of the total sky. But even with all the power of Hubble, and all the magnification of gravitational lensing, there are still galaxies out there beyond what we are capable of seeing.

(Credit: NASA / ESA / H. Teplitz and M. Rafelski (IPAC / Caltech), A. Koekemoer (STScI), R. Windhorst (ASU), and Z. Levay (STScI))

We can’t see farther because the Universe is only a finite age: it’s been a mere 13.8 billion years since the hot Big Bang.


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. There are an estimated 2 trillion galaxies contained within the yellow sphere drawn here, but that estimate is likely low, perhaps by as much as a factor of 3-to-10.

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

Beyond those limits, the story of our ultimate origin remains obscure.

The quantum fluctuations that occur during inflation get stretched across the Universe, and when inflation ends, they become density fluctuations. This leads, over time, to the large-scale structure in the Universe today, as well as the fluctuations in temperature observed in the CMB. New predictions like these are essential for demonstrating the validity of a proposed fine-tuning mechanism, and to test (and potentially rule out) alternatives.

(Credit: E. Siegel; ESA / Planck and the DOE / NASA / NSF Interagency Task Force on CMB research)

The Universe provides hints, but the necessary information to draw definitive conclusions eludes us.

From a pre-existing state, inflation predicts that a series of universes will be spawned as inflation continues, with each one being completely disconnected from every other one, separated by more inflating space. One of these “bubbles,” where inflation ended, gave birth to our Universe some 13.8 billion years ago, where our entire visible Universe is just a tiny portion of that bubble’s volume. Each individual bubble is disconnected from all of the others.

(Credit: Nicolle Rager Fuller)

Each glimpse into the great cosmic abyss continues our neverending pursuit of knowledge.

jwst change science

This image, of a dusty region of the Large Magellanic Cloud, was taken with JWST’s MIRI instrument at a wavelength of 7.7 microns. By measuring the Universe at unprecedented wavelengths, depths, sensitivities and resolutions, JWST can reveal details that have never been revealed before. From dust to stars to black holes and even to potential biosignatures, its capabilities could show us a Universe we never even expected to find.

(Credit: NASA / ESA / CSA / STScI)

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

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