How big does Hubble apear in the sky? We can see satellites sailing by at 23K miles, so at 350 miles, Hubble ought to be huge, but we’ve never seen anything unusual in size.
At that altitude, how bright does it appear?
How fast does it have to travel to stay airborne?
Since it’s not geosynchronous, it’s constantly in motion relative to the earth. How can it get clear images if it’s always moving?
Why wasn’t it launched into a much higher geosyn orbit? Wouldn’t it have a much better view from thousands of miles than it does from hundreds?
The reason you’ve never seen it is probably that you’re at too high a latitude. The cheapest orbit to launch into is one where the inclination is the same as the latitude of the launch site, and you won’t see a satellite at latitudes much higher than that, so if you’re further north than Cape Canaveral, you won’t see the Hubble or most other satellites. The only ones you will see from most of the US are those at higher inclinations (like the ISS, at the latitude of the Russian launch site to make it easier for them to send missions), or those in polar orbits (many communication satellites, for instance).
How big it appears is kind of irrelevant, since at that distance, any satellite is going to look like just a point of light, to the naked eye. In those circumstances, bigger objects will just look like brighter points of light. The Hubble is a fairly large satellite, so it’s probably impressive for those in a location to see it, but I can’t speak from personal experience there.
And there’s nothing in geosynchronous orbit (23k miles up) that’s visible to the naked eye. And geosynchronous, being higher, is more expensive, so it’s only used for things for which being geosynchronous would be valuable, which will be limited to things primarily intended to interact with the Earth (providing a television feed to a particular part of the globe, spying on a particular country, etc.). Since the Hubble is looking at distant objects, not the Earth, it doesn’t matter, so they put it in a cheaper low-Earth orbit.
I thought this picture (from Astronomy Picture of the Day on 05/23/2010) was great - it shows the space shuttle and ISS on the last mission, silhouetted against the sun. It shows the size of the ISS vs. the sun, which gives you an idea how big it is.
I see lots of satellites in New England - at least half a dozen Friday night (very clear night) between full dark and midnight. Most of them go roughly south-east to north-west.
Note that there are none between now and then. Also, the max altitude is 13 degrees and the magnitude is close to 3. Polaris is around magnitude 2, so in reality, your chances of seeing HST from Chicago with the naked eye are very slim.
Based on the orbit displayed at the link above, it doesn’t look like the HST passes over any of the US, except for Hawaii, but the orbital height of 559 km is more than enough to make it visible anywhere on earth.
It’s about 20 meters long, so when it’s directly overhead, its apparent size would be about 7 arcseconds. That’s about half the size of Mars at its closest approach. But it’s still big enough that if you manage to point a good-sized amateur telescope at it, you can see a vague shape.
Depends on many factors. There are web sites that calculate when satellites will be visible from your location, and those would include the brightness estimate. Very roughly speaking, a satellite that size can be as bright as the brightest stars in the sky, but usually not as bright as Venus.
Roughly 7 km/s.
It has guidance systems to keep it pointed at the target. The continuous motion isn’t a huge problem though, since there is no force on the satellite. (It’s not like you are fixed to a carousel - it’s more like a “teacup” ride, except the teacups are not connected to anything and are free to rotate (or not rotate).
It’s in a low orbit so it can be serviced by the Shuttle. Any higher and the Shuttle can’t get to it.
The view is better higher up, but only in the sense that the earth doesn’t block so much of the view. But of the objects that are visible, the image quality doesn’t get any better.
Also the further away you get from the earth, the easier the thermal design. If I remember correctly, the Hubble originally had issues with thermal stress on the solar panels. Basically as the satellite emerged from the earth’s shadow, the solar panels warmed up, and warped, which caused a disturbance that could interfere with observations.
Forgot to take the square root. The HST should be visible for 2670 km to each side of it’s orbit. That appears to make it visible in most of the lower 48 during some of it’s orbits, but it would be pretty low in the sky in the northern states.
This page from heavensabove.com shows Hubble’s orbital data, with an apogee height of 566 km and an inclination (to the equator) of ~28.5 degrees.
This page shows Hubble’s physical characteristics. It is just over 13 meters long and at 566 kilometers it subtends an angle of just under 5 arcseconds (human eye resolution is about 30 seconds of arc), so it is too small to resolve as anything more than a bright dot.
Like all satellites it shines by reflective sunlight so you need a dark sky to see it, but once it drops into the Earth’s shadow it disappears from sight. According to the page Hubble has a magnitude of -0.3 at its brightest, equivalent to some of the brightest stars in the sky, though it usually will appear much dimmer. You can plug your viewing position into this site and it will return the precise dates, times and locations you can see Hubble, the ISS, or just about any man-made satellite or astronomical object.
The “Heavens Above” website (also linked by jrepka) has a wealth of information on all sorts of natural and man-made objects in space. Check out the info on Iridium Flares. When one of these [66] satellites passes overhead (or nearly so) they can appear as bright as -8 (much brighter than the planet Venus at its brightest.)
Also, since satellites in geosynchronous orbits are relatively stationary with respect to the surface of the Earth (that’s the definition of “geosynchronous,”) you would hardly see one “sailing by.” If you trained a decent telescope on one for a night, you might notice it making a small “figure eight” against the background stars.
It is also somewhat confusing to describe satellites as “airborne,” which implies flying through the atmosphere. The HST is “in orbit” at about 17,500 mph (8 kilometers/second) 353 miles (569 km) above the surface of Earth.
While true that “it’s constantly in motion relative to the earth,” since orbit is actually “free-fall” that doesn’t matter. Its on-board gyroscopes keep the instrument pointed, rock-solid, at its target for hours at a time, and the on-board computers can aim the scope to the same exact target time after time, even years later.
“Wouldn’t it have a much better view from thousands of miles than it does from hundreds?” Actually, once you are above the Earth’s atmosphere, you can get as clear a view as it is possible to achieve. There would be no practical advantage to orbiting at a higher altitude. As well, there are frequencies of light to which our atmosphere is opaque, and orbiting a telescope like the HST allows us to explore these frequencies in detail.
Or to put it another way, Hubble is in the highest orbit the shuttle could reach with it as payload. Remember, it was launched by the shuttle.
Even at that altitude (which is about twice as high as the shuttle usually goes), it still loses altitude due to atmospheric drag. So one of the things the shuttle did on the servicing missions was to give it a boost back to the original altitude. Now that the servicing missions are over, its orbit will gradually decay until it reenters the atmosphere.
The Earth rotates beneath the orbit, with the result that that wavy shape doesn’t pass over the same land on every orbit. If you draw a wide band on the Earth, with the top and bottom of the band at the northernmost latitude and southernmost latitude on that wavy shape, it can pass over any point within the band. The northern edge of the band is right at Cape Canaveral, so it’ll pass directly over the southern parts of Florida and Texas at times, as well as Hawaii.
Thank you all so much for your responses - we are “gee whiz” “astronomers” - awed and fascinated by what we see but quite ignorant of the science and technology. But on any clear night from about 9:15 to 11:00 in the summer, we can sit on our deck in No. Cal. and count the satellites flying by, often more than half a dozen. Some are so dim we can only see them by averted vision. Most of them seem to be going from west to east on the east side of our house, occasionally one from east to west, and as a special treat, the occasional one from the west side of the house.
We saw the ISS a few years ago on July 4, just after the fireworks started. It was so bright it was clearly visible right through the fireworks.
I’ve bookmarked the links you all kindly provided and will use them to check on future sightings.