Apollo craft visible in LEO

[fireballxl5]

While talking to a guy who believes Apollo missions stayed in LEO while pretending to go to the Moon i explained that the craft would have been visible from Earth and people would have seen them like they do the ISS.

Surly we can see the ISS etc at night due to sun light reflecting off them. Is this correct?

[Data Cable]

Yes. Objects in orbit are typically naked-eye visible in the morning or evening, when the sun is below the horizon for the observer, but the orbiting object is still lit. They're not visible when the sun is above the horizon for the same reason stars are obscured by the blue sky, and not in the middle of the night because the orbiting object would be in the earth's shadow.

[tedward]

Also if I may add.

When the ISS is up our neck of the woods or just trying to get the hang one the scope I often see other sats around. Envisat is one. Also iridium among the easiest. You can see these yourself and a handy web site called "heavens above" (register and enter your location) will give you info on the good ones to spot.

Oops. ETA you would have to check sizes for comparison if that is a valid method?

[Kiwi]

Aug 14, 2008 7:31:18 GMT -4 Data Cable said:

Yes. Objects in orbit are typically naked-eye visible in the morning or evening, when the sun is below the horizon for the observer, but the orbiting object is still lit. They're not visible... in the middle of the night because the orbiting object would be in the earth's shadow.

The last sentence is sometimes true, but not always. As a general rule the greatest number of satellites can be seen around two hours after sunset (or before sunrise), but for how much longer something is visible depends on a number of factors:
1. The observer's geographical latitude.
2. The height of the object above Earth.
3. The angle its orbit forms to the equator.
4. The season.

For those who live between roughly 40 and 50 degrees north or south of the equator, the largest number of satellites can be viewed in one night for a period of up to a month or six weeks either side of the summer solstice. At this time the sun never gets far below the southern horizon at astronomical midnight for us southerners (or the northern horizon for northern hemisphere folk in their summer), so it lights up a large area of sky and therefore the greatest number of satellites above the viewer's location. In summer many satellites can be viewed all night because the earth's shadow is low in the sky.

On one occasion I saw the ISS five times on subsequent orbits in the same night, which I think is the maximum number possible. If its orbits and your location are favourable, it is possible to do this for a few weeks around the summer solstice. I'm just over 40 degrees south (near Palmerston North) so anyone further south in New Zealand will see the ISS higher in their sky if it is passing south of the country. It is also possible for me to see the ISS when it is above or south of Invercargill, but residents there can't see it because their sky is still lit up while mine is sufficiently dark.

I wonder how it can be seen if its not in sunlight. Do the crew shine a light down onto the Earth? If so then all they'd need to do is "rig for black" as they say about Navy ships and nobody would be able to see it.

Someone who knows so little about how we see satellites has no real business stating whether or not a particular object should be visible. A statement like this is so typical of HB ignorance.

[JayUtah]

At any given instant, the favorable Earth positions for viewing orbiters are the night-side edge of the terminator. Positions at ground level are obviously in darkness. However, positions hundreds of miles above ground level (i.e., at right angles to the illumination angle) are still in sunlight. Hence persons on the ground can see sunlit objects high in the sky.

We see this every morning and evening in our valley, whose principal axis is aligned roughly north-south. It is possible to see a faint shadow edge creeping down the western mountains in the morning, as seen from the east side; and a faint shadow creeping up the eastern mountains from the west side of the valley. At those times, someone on the ground could theoretically have just seen the sun set while also seeing something on the top of the mountain that is still in sunlight.

I agree, hoax believers have little knowledge of celestial observation.

[scooter]

When the new ESA cargo carrier was enroute the ISS, I decided to have a look see to determine if I could make it out. It was easily naked eye visible, though not as bright as the ISS. I would suspect the CSM, and certainly the non-TLI'd SIVB would have been easily visible to folks at the lower latitudes that Apollo orbited.
Between that, and the whole continuous big dish communications issue seals it for me...no way they could have done it while in LEO. Plus, their initial orbit before TLi was around 90-100 miles, not sure how long they would have stayed up at those low altitudes.

[Count Zero]

Aug 14, 2008 10:23:04 GMT -4 Kiwi said:

In summer many satellites can be viewed all night because the earth's shadow is low in the sky.

Excellent post, Doug! I had always held to the "2 hours after sunset..." rule. Imagine my surprise when, two years ago last month, I was crossing Puget Sound* on a ferry at around midnight and my wife & I observed more than a dozen satellites!

*Edited to correct: We were in the Georgia Strait, between Vancouver and Vancouver Island.

[gillianren]

In years when faire was not canceled, one of the highlights of the three weekends was the second Saturday, which most years roughly coincides with the height of the Perseids. A group of us lie out on the hay bales in front of the magic stage and watch the sky. We inevitably see satellites as we do--often more frequently than we see, um, meteors.

[LunarOrbit]

Didn't people see Sputnik? It was only about the size of a beach ball.

[Bob B.]

Aug 14, 2008 12:47:28 GMT -4 LunarOrbit said:

Didn't people see Sputnik? It was only about the size of a beach ball.

Most of the people who claim to have seen Sputnik were likely actually observing the upper stage of the launch vehicle, which was in a similar orbit. Sputnik itself was probably very difficult to see.

[Count Zero]

I just checked the math on my previous post: We were at ~latitude 49.1 at ~8:00UT on July 21, 2006. Any satellite more than 245 miles high, directly over our position, would have been in full sunlight.

[JayUtah]

Spent upper stages are responsible for a fair number of UFO reports. Upper stages are typically tumbled after payload separation to prevent residual thrust from integrating in a single direction and risking recontact with the separated payload. Thus spent stages tumble in unstable orbits for some time before eventually re-entering. A tumbling stage lit by the sun and seen under satellite viewing conditions near the terminator will appear to pulsate.

[Grand Lunar]

That reminds me Jay.

On the Star Trek forums, one guy there tries to push the UFO=alien spacecraft idea by citing who he calls scientists.
Much of what he provides is beyond my expertise, and I have no idea what source to look up.

Is there a good place that offers a comprehensive debunking of UFO claims (including sitings on radar or radiation burns)?
Or may I pick your brain in a different thread? I doubt the guy will visit here.
He's not a CT, far as I can tell.

[JayUtah]

I don't follow too many UFO discussions. At BAUT, Astrophotographer is the guy you want to talk to. He's done for UFOs what I've done for the Moon hoax.

[Grand Lunar]

Many thanks, Jay!