If they were all travelling at vastly different speeds, wouldn’t that affect how we see the constellations? I thought we’d all have to be travelling at a similar enough speed, otherwise they wouldn’t remain so constant? They only alter fractionally over 1,000’s of years, so their relative speeds around the galaxy can’t be significantly different, can they?
Why though? If you throw something out of a car window, it isn’t gravity that sucks it back in, it’s the air pressure outside. In space, you don’t have to worry about that, so if you can “throw” something beyond earth’s gravitational pull, why doesn’t it just get left behind?
Space travel is counter-intuitive to me and trying to comprehend a quasar gives me an headache..
The speeds are fairly high, but the distances are friggin’ huge, so it still takes a very long time for significant changes.
Because in space, you don’t have any air. If you toss something out the “back window” of the Solar System, there’s nothing to “stop” it: It’ll just keep on going the same speed it was. So if it starts off going at a small speed (in any direction) relative to the rest of the system, it’ll keep on going at that same speed relative to the rest of the system.
Looking at a graph on that page, Voyager 2 also got a big speedup from Saturn and a smaller speedup from Uranus. The flyby of Neptune led to a net slowdown, though changing the probe’s direction to leave the ecliptic.
I’ve been curious about what limits the planning of such trajectories. Do the probes have thrusters to correct for inaccuracies in flyby predictions? Was it difficult to schedule flybys of all four of the large planets?
One way of answering the question is to find out how far you have to go before the Sun looks like a point of light to the naked eye (like all other stars do from Earth).
The angular resolution of the eye is about 1 arc-minute, or 2.91e-4 radians. The diameter of the sun is 1.38e6 km, so using the small-angle formula gives us a distance of 4.74e9 km.
Pluto’s orbit varies from 4.44e9 to 7.31e9 km, so it’s in the right ballpark–from that distance, the sun would still be the brightest star in the sky, but still look like a point.
Another way of looking at it: how far away do we have to get before the Sun is no brighter than the brightest (non-Sun) star on Earth? Well, the Sun has a magnitude of -26.74, while the next brightest star Sirius has magnitude -1.47. If my calcs are right, that corresponds to a distance of 113240 AU. That’s 1.79 light-years–a good distance but still less than halfway to the next star.
If you were stood on the last object orbiting our sun(I know it used to be Pluto, but isn’t there supposed to be something else now?), bearing in mind there’ll be no twinkling unless you’re viewing it through an earth-like atmosphere, how different would it appear than all the other points of light?
Would it appear to be significantly brighter than the North Star is compared to most other stars?
How about another one?
How bright would another star have to become to be visible during the day? Would a supernova be spotted by the naked eye on a clear sunnny day?
I was simplifying a bit, sometimes it’s best to use multiple gravity assists. For example, the Cassini probe was swung by Venus twice and Earth once before heading out to Jupiter and on to it’s final destination Saturn.
Fun fact, it take more energy to send a probe into orbit around Mercury than to escape the solar system.
The Voyagers made use of a rare alignment of the outer planets which won’t occur again for another 175 years, the grand tour.
As I said above, 150 to 450 times as bright as a full moon. It would hurt your eyes to look at it directly.
Venus, Jupiter and occasionally Mars can be seen during the day. The brightest star, Sirius, isn’t bright enough.
That depends how close the supernova is. When Betelgeuse supernovas, it is expected to outshine the moon, so would be easily visible. The last supernova visible to the naked eye during the day was in 1604. The first was recorded in 185, and there have been a handful since then.
According to the chart on this Wikipedia article, the Sun would be brighter than the full moon on Earth if you were on Eris at the farthest point of its orbit, and a little dimmer than the full moon on Earth if you were on Sedna. It’d probably still be bright enough to cast shadows.
By the way, just to be crystal-clear on this: it’s a common misconception that the North Star is the brightest star in the sky. It’s somewhere around 45th brightest. Even if you knew that already, I figured I’d throw that in to combat ignorance of other people who might read this thread.
According to the above link, an object would have to have an apparent magnitude below -4 (lower numbers mean brighter) to be visible on a clear sunny day. Some historical supernovas have indeed gotten brighter than that, most notably the one in 1006 AD.
In some ways, it’s more an art than a science. The particular pattern of flybys that the Voyagers used only comes up every couple of centuries, but it’s not too uncommon that clever mission planners can come up with some interesting pattern of flybys or another. What’s interesting is that computers are fairly poor at this: Give a computer a rough trajectory plan, and it can smooth it out quite nicely, but it’s much harder to make the computer give you the rough plan.
Oh, and the probes do all have onboard thrusters to do course corrections. Ideally, you shouldn’t strictly speaking need them, but ideal cases never actually happen. There are always some errors and imprecisions that you need to correct for on the fly. In practice, though, if you plan properly, you can get away with using very small thrusters and fuel reserves.
To expand, based on Dr. Strangelove’s calculation above, the Sun would be at just about the limit of resolving, so for any one rod or cone in your eye, the Sun will be just as bright as if you were looking at it in Low Earth Orbit. In LEO, the Sun will form an image over more of your retina, but will have the same intensity.
So if you look at the Sun without protection from Pluto, you’ll be blinding yourself, one rod or cone at a time.
Another interesting question is “at what distance from both of them do Sirius AND the sun both fail to be the brightest stars in the sky?”
Sirius is the brightest star in our sky because it’s a decently bright star that is pretty damn close to us (albeit not as close as alpha centauri). At some distance, it would start to fade in the background and be outshone by one of the no-kidding BRIGHT stars like Rigel, which might in fact be the one to first outshine Sirius. I guess Canopus and Betelgeuse would be good candidates too.
There are some nasa photos that show the sun from that vicinity.
There were not terribly different than the artist rendering posted here, but lower resolution looking.
Sun is still a really really big thing to be seeing from pluto distance
It does not look like another star, but not like the sun either.
It more resembles like looking at a planet that is very bright, stars in the sky have no appreciable size to our eyes because they are so far away.
I can not remember what they were from, one of the voyagers perhaps?
Maybe someone remembers and can link one or something, i cant seem to find them.
The answer depends on which direction you head. If you’re headed in the general direction of Sirius, you’ll have to go well past it (as in further beyond it than it is from Earth) before it stops being brightest. And there are other nearby stars that have similar absolute magnitude as Sirius. If you head in their general direction, they may become the brightest before more distant very bright stars.
Altair (distance 16.6 ly, abs mag 2.2), Vega (distance 25 ly, abs mag 0.58), Fomalhaut (dist 25 ly, abs mag 1.72), and Procyon (dist 11 ly, abs mag 2.66) are candidates (compare with Sirius (dist 8.6 ly, abs mag 1.4). In the case of Procyon, you would also be headed not too far off the direction of Sirius, so you’d have to get fairly close before the little dog outshines the big dog.
I did a little data mining with the HYG star database, and our intuitions were mostly correct, with some minor surprises.
Sirius is indeed the next brightest star, almost no matter which direction you head. The best I found was in the direction of Barnard’s Star, 2.24 ly out. It’s almost opposite the direction of Sirius, but as said, Sirius is so much brighter than Sol that it outshines it as soon as you get a little distance.
As best I can tell, there’s no direction where Sol is the brightest star and not also the closest. You just can’t get far enough away with Sirius dominating the neighborhood.
As Chronos said, you want to head in the direction of Alpha Centauri. But you don’t get all the way there–as said above, Sol remains the closest star. Rigil Kentaurus is brighter than Sol, so you have to go less than halfway (2 ly).
Yes. In almost any direction,
[1] Sol (white main-seq) will be the brightest star for a while, then
[2] Sirius (Alpha CanisMajor, white main seq.); but eventually, no matter which direction you head,
[3] Canopus (Alpha Carinae, a bright white giant) will be brightest. Then long after Canopus has dwindled into obscurity,
[4] Alnilam (Epsilon Orionis, the large blue supergiant star which is in the center of Orion’s belt) will be the brightest star. Maybe.
Rigel (Beta Orionis, the blue-white supergiant that is the Hunter’s left foot) is interesting. In most directions, but not all, it will become the brightest at some point. For example, if you head for Canopus, Rigel will become the brightest after 660 light-years when you’ve left Canopus far behind. And if you head from Earth in the opposite direction, directly away from Canopus, Rigel will become brightest briefly, after 225 light-years.
There seems to be some controversy about the distance to Deneb, the blue-white supergiant in Cygnus. It is probably similar to Rigel in becoming the largest star at some point for most directions of travel from Earth.
Questions:
(1) Is it true that Alnilam (in the center of Orion’s belt) will eventually be the brightest star no matter in which direction you head?
(2) What stars will eventually become the brightest if you head in some certain direction AND also become the brightest if you head in the OPPOSITE of that certain direction? I’ve implied that Sol, Sirius, Canopus, Alnilam, Rigel and probably Deneb all satisfy this. Are there any others?
Using Wikipedia’s values, Deneb is 800 parsecs away and has a whopping -8.38 absolute magnitude. This is very different from the HYG data.
With Wikipedia’s numbers, it is Deneb rather than Alnilam that dominates the sky at some point (once you get far enough away from Canopus) almost no matter which direction you travel.
