I recently saw a post regarding the discovery of a new nebula by a hobbyist. I would like someone to explain how this is possible given the thousands of satellites we have.
Somewhere around 95% is undiscovered. Pretty much all of our satellites are for something other than observing space, and our telescopes are getting more powerful, making more things observable within observable space. Plus, looking at things very far away takes a lot of time, because there’s not a lot of light headed from that thing directly to us, so we have to wait for enough light to come to make a lm image.
The volume of the Earth is about 1.1E21 m^3. There are great swaths of the Earth’s surface that haven’t been explored (think of much of the abysmal ocean plains). That is literally just barely scratching the surface of the Earth. We have ideas of what’s on the inside, but anyone who tells you we know everything about it are lying.
The volume of the observable universe is about 4E^80 m^3. This is a volume about 4E59 m^3 times larger than the volume of the Earth. 4E59 is a large number–if you think you understand how large this number is, then you do not understand how large this number is.
The fastest space probe not in orbit is Voyager 1. If it was heading for Proxima Centauri (our nearest neighbor) it’d take over 70,000 years to reach it. It’d take about 100,000 years to cross the Milky Way traveling at the speed of light (light is fast).
We suspect there are over 125 billion galaxies in the observable universe. Start counting. If it takes you 1 second for each number it’d take you almost 4000 years to finish (no eating, sleeping, or bathroom breaks!). Each galaxy has on average around 100 million stars. So counting stars instead will only take you a few trillion years.
TL/DR — Space is big.
This isn’t really an answerable question because what do you even count as “discovered”? That’s a subjective measurement.
Also, almost no satellites look at space. The overwhelming majority of satellites are used for Earth-based applications like communications or Earth observation. At any given time, there are only a dozen or so space telescopes in operation, and there have been maybe 100 or so *ever* since the spaceflight era started in 1957.
The discovery of a new nebula by a hobbyist is possible because of the advances in technology that allow us to access more detailed images of the night sky. With the help of powerful telescopes, binoculars, and digital cameras, amateur astronomers are able to capture and observe the night sky in greater detail than ever before. With the help of powerful software, they are able to identify and classify different objects in the night sky, including nebulae. This is made possible by the thousands of satellites that are constantly monitoring the night sky and providing detailed images of the night sky.
The vast majority of satellites don’t look at space. That’s just space telescopes like Hubble, JWST, etc. And telescopes work pretty well right on the ground. Really just no connection between “discovering nebula” and “having thousands of satellites”.
Faint objects require a very long exposure time in the right wavelength. In the case of the nebula you’re talking about, O III emissions. The person who discovered it was specifically scanning the night sky with long O III narrowband exposures looking for unknown, faint sources of O III emission.
The combination of having to look in every direction, in every wavelength, with exposures of potentially unknown lengths, at many different scales means that it’s still possible to find things like this in the milky way that are undiscovered.