Given the scope of the universe and how long it takes light to reach our Sol system, I wonder if there is any documentation of stars appearing (their light finally reaching us) or disappearing (the light-producing process coming to an end) in the historical record.
I did see a previous post on the Crab Nebula's appearance, but really curious about the opposite; what about stars going out?
One thing I want to clear up before diving in: the distances to the stars is essentially irrelevant on the timescale of their lifetimes. Every star you can make out individually with the naked eye is no further than ten thousand or so light years, meaning that even for the fastest lived stars, you're seeing them essentially as they are now.
The Crab Nebula IS an example of a star "going out." It is the remnant of a star that exploded (went "nova", more on that in a second) at the end of it's life. While a pulsar was created at the center, we cannot see that with the naked eye.
That word, "nova", literally means new and comes from the fact that a star going nova at the end of its life can often appear to be a new star. Often, the progenitor star wasn't even visible to the naked eye, but even if it was, the nova will be far far brighter for the week or so that it's happening, giving the appearance of a brand new star in the sky.
Humans have witnessed plenty of these over the years, and written them down. Many, we were later able to associate with remnants once telescopes were invented. Sadly, unlike with eclipses, we can't use these records to help fix the historical chronology, because unlike with eclipses, we can't "run the clock backwards" to know exactly when a certain supernova happened. With eclipses we can do that - we are told, for example, that there was an eclipse in the ninth year of the reign of Assyrian king Ashur-dan III. Since the only total solar eclipse in that part of the world anywhere near that period was June 15, 763 BC, we can figure out the exact dating of Ashur-dan III's reign - and by extension the monarchs around him.
Your question though, was have we seen any ACTUAL new stars "switch on" - not short lived nova but actual real stars. And the answer is no, for a few reasons.
One, it's not that common. Three new stars form a year on average jn the Milky Way, and the vast vast majority of the Milky Way is too far and too dim to be seen. Remember, almost all stars you can see are within a few thousand light years.
Two, stars form in dense regions of gas called molecular clouds (aka "stellar nurseries") which will partially obscure the forming stars. The most famous of these is probably the "Pillars of Creation", a part of the Eagle Nebula made famous as one of the first clear pictures taken by Hubble after its optics were fixed. These dark clouds dim the light from the forming stars until they are bright and hot enough to push the enveloping dust away with their stellar wind.
Which plays a part in point three - stellar formation is a slower and less violent process than stellar death, and acts on a longer scale than a human lifetime. A collapsing cloud of gas heats up as the gas falls in, and the protostar will start to glow from that heat. This heating up takes time. Once fusion temperatures are reached it will quickly spread throughout the core, but the outer layers of the protostar that will become the photosphere (the bright outer part that you see) will still take more than a century to reach full heat. In fact, depending on the size of the star, possibly orders of magnitudes more. So no human lifetime is likely to recognize as new a point of light that gradually comes into being.
So what's the youngest star you can see? One of the most famous young star clusters is the Pleiades, which to the naked eye appear as 7 stars jn a tight group. They are sometimes called the Seven Sisters and appear in many cultures mythology. The youngest is about 75 million years old. A few years back, Cal astronomers found a dust disk around a star called AU Mic that appears to be only 12 million years old. But there are newer stars still - within the Pillars of Creation, mentioned above, we can see with Hubble there are stars that are forming or have formed which are already in the process of blowing away the molecular cloud, revealing themselves.
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