There are many phenomena that light up our night skies; from the astronomical (stars, planets, galaxies) to the human-made (satellites, rockets, and ever-increasing light pollution).
These different sources contribute to whether we can see faint objects and fundamentally limit the performance of our telescopes, so we build bigger ones to collect even more light.
For example, light pollution in the heart of Sydney makes the sky about 30 times brighter than that at Australia's Siding Spring Observatory, and a full moon contributes about five times more background light than a night with a new moon.
But what if we removed these effects?
pace telescopes such as the James Webb Space Telescope are at an orbital position known as L2; far away from city lights, Earth's atmosphere and even the moon.
So surely they can see even the faintest galaxies?
While it is certainly true that space telescopes can see much fainter astronomical objects than ground-based telescopes, that doesn't mean that they have fully escaped background light - they have their own form of light pollution to deal with.
Where does this light come from?
Known as "zodiacal light", this background glow comes from sunlight that is reflected off of tiny particles of dust inside our solar system (about the width of a human hair).
We can actually see this glow if we go to a very dark sky site such as Siding Spring Observatory. It appears as a roughly triangular shape on the horizon along the position of the zodiac.
The zodiac, related to but not to be confused with "star signs", is a belt-light region of the sky that surrounds the ecliptic (otherwise known as the plane of the solar system).
Could this dust be from the early solar system, when the planets were still forming?
Well, light from the sun causes the tiny grains of dust in their orbits to experience drag, which reduces their angular momentum.
This leads the dust to spiral in towards the sun and essentially be destroyed.
In order to account for the amount of dust we see, new dust needs to be created all the time. Therefore, astronomers believe that this dust is created from comets entering and leaving the inner solar system, as well as collisions in the asteroid belt, rather than being relics of the early solar system.
Other planetary systems also contain a large amount of dust close to their stars, known as exozodiacal dust.
These dust clouds, while interesting in their own right, are very problematic for planet hunters wanting to find Earth-like planets.
This is for two reasons: the first is that the light from these dusty clouds can outshine their planets by a lot, making it very hard to detect and characterise their already faint signals. Even more problematically, these clouds may be clumpy, and so could produce a signal that looks like a planet itself.
Nevertheless, despite the zodiacal and exozodiacal light being a nuisance for space telescopes, seeing our dusty solar neighbourhood on a remote, clear, dark night is still one of the best parts of backyard astronomy.
- Jonah Hansen is a PhD student specialising in space interferometry at Mount Stromlo Observatory, at the Australian National University.
