Visually, I mean. And, of course, I’m aware that, barring a truly spectacular comet, the naked-eye answer is the Sun or the Moon, 30 minutes of arc each, accept no substitutes. And of course the objectively largest “object” is some cluster of galaxies a couple of billion parsecs away visible only with the 3 or 4 largest telescopes and not familiar to anyone but professional astronomers and collectors of astro-trivia.
But as I understand it, and connected to the recent question about the Andromeda Galaxy, there are a number of objects too dim to be seen “in their full glory” with the naked eye, but subtending a greater arc in the sky than the Sun or Moon. I was surprised to find out how big the Gum Nebula in the southern skies actually is, when viewed through a telescope.
So, given that, if we could see far more faint objects than we presently can, what would be the things that would appear the biggest to us?
Side question: given that we’re on a convergence course with Andromeda, what would be the visual effect as it gets closer? And what is likely to happen when the two galaxies actually converge? Will there (probably) be any significant effects to Earth/the Solar System?
The answer of coulrse hinges very strngly on your definintion of “object”, but if Andromeda qualifies, I’d suggest the Milky Way ought to also. Even using the naked eye as a sensor that formation subtends a vast arc of sky, ~180 degrees x (wag) ~10-15 degrees.
I’ve had a celestial globe for a long time and it has the wonderful feature of being able to be oriented to any latitude so you can see what the sky looks like from that place (those places) on earth. There is an orientation where the Milky Way is completely visible – it’s on the horizon in every direction. Except for the obvious difficulties with “town glow” and trees and mountains and structures near the horizon to block your view, such a view of the Milky Way would be hard to top.
I don’t know about large, dim objects in our sky, but I can tell you about the impending collision. When the Milky Way Galaxy collides with the Andromeda Galaxy, there will be … a whole lot of nothing. Galaxies are mostly empty space. Actual collisions between stars (or their planetary systems) will be about as common as two gnats in the Grand Canyon running into each other. Oh, and the interstellar dust clouds will swirl together.
Visually, it would be fairly boring, since these things happen on immense timescales. Our descendants nearly three billion years from now will see Andromeda as a very large, bright patch in the sky much like the Milky Way, only brighter. But, it won’t look to them like it’s moving any more than it does to us today. Vastly speeded up, it will look something like this when viewed from afar.
As to whether it will affect us; perhaps. Although the actual likelihood of two stars colliding is extremely small, a passing star could certainly seriously disrupt the orbits of the outer planets and other objects which, in turn, could impact the inner planets. Earth could suddenly find itself bombarded by massive comets. Wheee!
I haven’t read it, but I assume Finnegans Wake must have some puns that work on more than three levels, especially if you include puns across multiple languages.
There are gasseous nebulae several times the apparent size of the Sun and Moon in the sky, like perhaps the size of your outstretched hand and fingers at arm’s length. You can get nice photos of these with an ordinary camera on a tripod or, better, a sidereostat (sp?), and a normal lens, with an extended exposure.
And here’s where I have to point out that there’s no evidence that the Milky Way and M31 are going to collide, and in fact some evidence that they won’t. It’s an absolute fact that they’re currently getting closer together, as shown by the Doppler shift, but that only tells you one component of the motion. To know whether it’ll hit us, or just swing past us, we’d need to measure its apparent motion in the sky, and we don’t have measurements that are precise enough or over a long enough timescale to determine that. Plus, the two galaxies should have a sufficiently short orbital period, compared to their ages, that if they were going to collide, they should have already done so, long ago. It makes for a nice soundbite to say that they’re going to collide, but the evidence doesn’t back it up.
While I grant that the Milky Way (visual entity, not the Galaxy) is a “thing” in the sense I meant here (i.e., the disk of our galaxy as seen from within it), I was actually looking more for the sorts of things Napier refers to here, with ideally some specific examples and their sizes.
I’m not talking constellations or asterisms, or other coincidental not-physically-united patterns, but also not necessarily “single objects” in the sense that a star is and a galaxy is not – Andromeda, a globular cluster, the Magellanic Clouds would be examples of gravitationally-bound collections of things that would be “an object” visually.
It’s as much a matter of time of day and season as it is latitude.
If you will look at this article dealing with the North Galactic Pole (assuming you’re in the Northern Hemisphere) you’ll see that the NGP is in the constellation Coma Berenices. For the Milky Way to be on the horizon, Coma Berenices (and the NGP) must be as close to overhead as possible. All you have to do is get a star map and see at what hour(s) and in which month(s) that happens near your location.
Since the NGP has a Declination of 27 Degrees and change, you’ll need to be at 27 Degrees North (on the latitude of Lake Okeechobee in Florida) for the NGP to get to zenith point (directly overhead) and the further away you are from 27 Degrees (Tennessee is in the 35-36 1/2 latitiude range and thus nearly 10 degrees north of that point) the lower the NGP will be from zenith. So most of the USA is far enough north of the optimum latitude that the full effect of Milky Way on the horizon can’t be had.
But the NGP getting to zenith happens at a different hour every day. So you’ll need a star map or some other reference like that to find when it happens for you.
For those in the Southern Hemisphere the South Galactic Pole (in the constellation Sculptor) being at zenith should cause a similar phenomenon.
It’s been a good deal of time since I last went through all this exercise of translating points in the sky to places on earth so I could be way off, and I hope somebody more current with their astronomy can correct my mistakes.
