Jarbabyj’s thread about why people with poor vision can see stars led me to a question I’ve been curious about.
Suppose for the purposes of this thread that I have perfect vision – but no access to optical instruments of any sort (binoculars, telescope, etc.). So I walk outdoors on a clear night and look up, and do this repeatedly at various seasons and places on the globe.
Besides the roughly 6,000 naked eye stars, what objects might I be able to see?
Insofar as I can tell, I’m going to be able to see:
[ul][li] six planets – Mercury, Venus (near sunset or sunrise as appropriate), Mars, Jupiter, Saturn, and Uranus[/li][li]one asteroid – Vesta[/li][li]the Moon[/li][li]three or four galaxies – M-31 (Andromeda), the two Magellanic clouds, and maybe M-33 (Triangulum)[/li][li]a few nebulae, but I’m not sure how many or which ones[/li][li]from time to time, a comet[/li][/ul]
Not an “object” as such (but then neither are the Magellanic Clouds or the Andromeda Galaxy), but in addition to the 6,000 or so naked eye stars you could see our own galaxy in the form of all the stars making up the Milky Way.
You didn’t specify whether they had to be above the atmosphere, so I’ll add planes, the northern or southern lights… maybe a cloud, though they’re hard to make out at night.
Also meteors and meteor showers. (ditto-ing Otto, discovered on preview.)
Are there any artificial satellites that can ever be made out with the unaided eye?? I’m not sure about that one.
If the sky is really dark, you can see interplanetary dust as a band of light. It’s known as zodiacal light.
There are some dark nebulae that can be “seen” against the Milky Way. The most prominent one is the Coalsack.
And obviously, lots of terrestrial flying creatures, manmade objects (balloons, aircraft, satellites, rockets), the Earth’s atmosphere (the blue stuff) and various atmospheric phenomena (lightning, clouds).
[QUOTE=Polycarp]
[b[li]a few nebulae, but I’m not sure how many or which ones[/li][/QUOTE]
The Great Nebula in Orion is plainly visible to the naked eye, even with some light pollution, though it looks most amazing under a dark sky. Southern Hemisphere observers can see the Coal Sack, and the Pipe Nebula is visible in a dark sky.
Under favorable circumstances, someone with excellent vision can see three or four moons of Jupiter. The rest of us can easily see them with binoculars.
47 Tucanae is another globular cluster visible to the naked eye. There are a few others that are also naked eye objects as well as a number of other open clusters.
The four Galilean satellites of Jupiter are visible with the naked eye. They all have apparent magnitude less than 6.
There are hundreds or thousands of small asteroids whose orbits cross the earth’s. The recent close passage of Toutatis was not visible to the naked eye, but in 2028, the Asteroid 1997 XF11 may come just close enough to be visible.
Aurorae.
Noctilucent clouds.
If you’re near a certain type of erupting volcano, you might see a fire fountain, a gush of incandescent lava that has been known to reach as high a mile above ground.
