Pondering the infinitely large and small, … there’s the neutrino. Grok this:
“The sun is emitting neutrinos like mad, so that about a hundred trillion of them pass through your body every second , …” — Carroll, Sean (2016-05-10). The Big Picture: On the Origins of Life, Meaning, and the Universe Itself (p. 177). Penguin Publishing Group. Kindle Edition.
[Wikipedia] “About 65 billion (6.5×10^10) solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth.”
So, I got out a ruler and drew a square on a piece of paper, each side 1 centimeter long. Which looked like less surface area than the nail on my little finger. Imagine seeing 65 billion things passing through that space. Like crazy invisible “hail ” everywhere. All the time.
And an amazing property: currently the neutrino’s speed is effectively the speed of light (within measurement error) and likely has non-zero mass! — maybe one millionth that of the electron . And it comes in flavors. And maybe neutrinos do not interact with each other, just like photons.
As far as size, that’s spooky: “… , it does not have a size in the same sense as everyday objects.”
The saga continues with the Big Bang model and research on the cosmic microwave background; also the Standard Model of particle physics. Chasing the ghost particle.
 Neutrino mass inferred from “the experimentally established phenomenon of neutrino oscillation.”
Update March 7, 2017
Supernova 1987A: “This was the first time neutrinos known to be emitted from a supernova had been observed directly, which marked the beginning of neutrino astronomy. The observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in the form of neutrinos.”
Update May 19, 2020
Regarding supernovas, observational astronomy has really advanced since 1987.
Symmetry Magazine > “The supernova that keeps on giving” by Shannon Hall (04/28/20).
Although astronomers now spot thousands of supernovae every year, an explosion close enough to be seen with the unaided eye is still a rare event. In fact, the cosmic explosion—dubbed SN1987A or just 87A for short—remains the closest supernova that has been seen in nearly four centuries.
Before 1987, however, much of our understanding of supernovae was based solely on theory.
[When] a type II supernova erupts … the bulk of the star comes crashing down toward its core, forcing it to collapse into one of the densest astrophysical objects known, a neutron star.
At least that was the theory. If true, the action would release a huge stream of particles called neutrinos. And because they would pass through the bulk of the star unimpeded, they would arrive at Earth even before the explosion could be seen as a blast of light. (In fact scientists now think that it’s not the bounce that blows up the star, but the neutrinos.)
[Launched in 1990, Hubble Space Telescope’s] early images revealed what other telescopes had only hinted at: a thin ring of glowing gas that encircled the dying ember that 87A left behind, with two fainter rings above and below. These were clues that the star had dumped a lot of gas into space tens of thousands of years before it exploded. A previous outburst, likely from a red supergiant, could have whittled the star down to expose its hotter, bluer innards. Or perhaps two stars had collided together; this would have shed a lot of gas and left behind a hot mess.