The short answer
Under an electron microscope, a coronavirus looks like a tiny, roughly round particle with a fringe of club-shaped spikes sticking out from its surface. In cross-section the fringe can look like a crown or a solar corona, and that’s where the name comes from: corona is Latin for “crown”. The particles are often seen in clusters on the surface of infected cells, or packed inside small sacs within them.
Under an ordinary light microscope, including any home, school or hobby microscope, a coronavirus can’t be seen at all. It’s far too small.
How big is the coronavirus?
SARS-CoV-2, the virus that causes COVID-19, has been described in early electron microscopy studies as roughly 60 to 140 nanometres across, not counting the spikes. A nanometre is a millionth of a millimetre. For comparison:
| Object | Approximate size |
|---|---|
| SARS-CoV-2 particle | ~0.06–0.14 micrometres (60–140 nm) |
| Typical bacterium | ~0.5–5 micrometres |
| Human red blood cell | ~7–8 micrometres across |
| Human hair | Often ~50–100 micrometres wide |
Hundreds of coronavirus particles could line up across the width of a single red blood cell.
Why you can’t see it with a light microscope
The limit isn’t magnification, it’s resolution. Because of the wave nature of light, an ordinary light microscope can’t separate details much smaller than roughly 0.2 micrometres (200 nanometres), even with the best lenses. A coronavirus is smaller than that limit. More magnification would only enlarge a blur.
Specialised fluorescence methods can detect tagged virus particles as glowing dots, and some “super-resolution” techniques go below the classic limit. But these are research instruments, and even they don’t show the particle’s shape the way electron microscopes do.
How scientists image it
Electron microscopes use beams of electrons, which have a much shorter wavelength than light. That lets them resolve far finer detail:
- Transmission electron microscopy (TEM) sends electrons through a very thin slice of infected cells or a prepared sample. Virus particles appear in cross-section as dark-edged circles with a fringe of spikes, sometimes with dots inside, which are the internal protein-and-RNA core.
- Scanning electron microscopy (SEM) scans the surface of a sample. It shows virus particles as small bumps or balls studding the surface of a cell, with a three-dimensional look.
- Cryo-electron microscopy (cryo-EM) images rapidly frozen samples without staining. Combining many images lets researchers work out the detailed 3D structure of the spike protein itself, which helped with vaccine and drug design.
Electron microscopy of infectious viruses is done in specialised, contained laboratories, often on chemically fixed (inactivated) samples.
What the images show
- The spikes. Spike proteins, studding the surface, are what give coronaviruses their crown-like appearance. The spike is the part the virus uses to attach to and enter cells.
- The envelope. A fatty membrane surrounds the particle. That’s one reason soap and alcohol-based sanitisers can damage coronaviruses.
- Particles with cells. Many published images show virus particles budding from, attached to, or packed inside the cells they infect.
Other coronaviruses, such as the original SARS virus and MERS, look broadly similar in EM images. The family resemblance is strong enough that you generally can’t tell them apart by shape alone.
Are the colours real?
No. Electron microscopes don’t record colour: the raw images are greyscale. The vivid gold, red, blue or purple coronavirus pictures you see in the news are digitally colourised by image specialists to make the virus stand out from the cells around it. The colours are a choice, not a property of the virus.
Lookalikes and misidentification
Spotting coronavirus in electron micrographs of tissue is harder than it sounds. Some normal cell structures, such as coated vesicles and parts of the cell’s own transport machinery, can look like round particles with a fringe. Some researchers have pointed out that structures reported as coronavirus in tissue samples may actually have been these lookalikes. Confirmation usually relies on other methods too, such as detecting viral RNA or proteins.
This is a good example of why microscopists are cautious about artifacts and lookalikes. Looking like something isn’t always the same as being it.
What you can see at home instead
You can’t see viruses with a home microscope, and you shouldn’t try to sample or culture anything from a sick person. But you can see a lot of other microscopic life:
- Bacteria at 1000x in a stained smear of yoghurt or dental plaque, as described in our guide to viewing microorganisms under a microscope.
- Your own cheek cells and their nuclei, stained with methylene blue. See methylene blue staining for microscope slides.
- Pond protozoa, algae and tiny animals.
For a wider tour of what is and isn’t visible, see our guide to what everyday things look like under a microscope.