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Thread: sky lights

  1. #1
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    sky lights

    Two questions:

    Question 1:

    While observing Saturn in my 'scope, a faint point of light streaked across the field. I looked in the sky, but it wasn't visible.
    Has anyone else see such an occurance in their 'scopes?
    I hypothesize it to have been one of three things:
    -A high flying aircraft (but not too likely, since I saw no running lights)
    -A small satillite
    -A tiny meteor (though there was no trail from it)
    What do you, the people, think?

    Question 2:

    It seems that Jupiter appears brighter in the sky.
    I observed it when it was in the early morning sky in Febuary and early March. Then, I left my home town, and didn't really observe it again until I came back early May. It seems brighter now than it was during the earlier months.
    Could it be that since we had our closest approach to the giant planet that it appears brighter? Or are my eyes just playing tricks on me?

  2. #2
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    Jupiter was closest to us on May 5, 2006. So it should be brighter now.
    Everything I need to know I learned through Googling.

  3. #3
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    Quote Originally Posted by Grand_Lunar
    While observing Saturn in my 'scope, a faint point of light streaked across the field. I looked in the sky, but it wasn't visible.
    Has anyone else see such an occurance in their 'scopes?
    I hypothesize it to have been one of three things:
    -A high flying aircraft (but not too likely, since I saw no running lights)
    -A small satillite
    -A tiny meteor (though there was no trail from it)
    What do you, the people, think?
    This happens often. It was probably a piece of "space junk" orbiting the earth. Many of my long-exposure images of deep-sky objects are contaminated with streaks. The ones with regularly-varying luminosities are probably booster stages, etc, rotating end for end; the ones that start and/or end in the frame might more likely be meteors. It happens.

  4. #4
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    Quote Originally Posted by Grand_Lunar
    Two questions:

    Question 1:

    While observing Saturn in my 'scope, a faint point of light streaked across the field. I looked in the sky, but it wasn't visible.
    Has anyone else see such an occurance in their 'scopes?
    I hypothesize it to have been one of three things:
    -A high flying aircraft (but not too likely, since I saw no running lights)
    -A small satillite
    -A tiny meteor (though there was no trail from it)
    What do you, the people, think?
    Probably a tiny meteor. I’ve seen them in the distance along the horizon when I look at airplanes through my binoculars. I think there are quite a lot of little biddy dim ones that we can’t see unless we just happen to be looking through binoculars or a telescope.

  5. #5
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    It could have been either a satellite or a meteor, depending on how fast it was "streaking". If it took a small fraction of a second, I would bet on "meteor". If it was visible long enough for you to focus on it, I would say "satellite". If it was a satellite and you remember the time, Heavens Above might be able to tell which satellite it was.

  6. #6
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    The object took just over a second to cross the field of view. So, I would venture that it was too slow to be a meteor, too fast to be a plane.

    Space junk now sounds most probable, given how faint it appeared. Or does the brightness depend on other things too, like size and distance from the Earth?

    Oh, and thanks for the input ToSeek. I didn't think that Jupiter really does appear to change brightness depending on our distance. But, it makes sense that it would.

  7. #7
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    Well, that depends upon the angle of your field of view. Satellites aren't exactly slow! If you're looking through a 200x telescope, one can streak across in about half a second.

    Meteors are very difficult to see as they're rather dark. When one hits the atmosphere, and heats up to the point where it's bright, it always leaves a trail. It may be short or fleeting, but it's there, and small meteorites appear as streaks. You described a point souce, which to me means satellite.

  8. #8
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    Quote Originally Posted by mugaliens
    Meteors are very difficult to see as they're rather dark. When one hits the atmosphere, and heats up to the point where it's bright, it always leaves a trail.
    Meteors are the trail, it's meteoroids that are dark. If Grand_Lunar's object was faint even in the scope, it probably was too dim to see naked-eye.
    Space junk now sounds most probable, given how faint it appeared. Or does the brightness depend on other things too, like size and distance from the Earth?
    And orientation. There are the (in)famous Iridium satellites that suddenly flair to even daytime-viewing brilliance if their mirror-like antennas catch the sun right.

  9. #9
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    Quote Originally Posted by Grand_Lunar
    Oh, and thanks for the input ToSeek. I didn't think that Jupiter really does appear to change brightness depending on our distance. But, it makes sense that it would.
    I think it has more to do with how much of Jupiter's sunlight side is facing us than anything else. At opposition, it's full on to us.
    Everything I need to know I learned through Googling.

  10. #10
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    Most satellites cross the visible sky in about 10 minutes. Let's take a look at one example from Heavens Above happening soon: Resurs 1-4 Rocket 3.3 23:06:03 18° SSE 23:10:08 89° NW 23:15:28 10° NNW

    That's 62 degrees in 9 minutes and 25 seconds, or 9.41 minutes, which comes to an angular velocity of 6.58 degrees per minute, or .10976 degrees per second.

    An 8" Celestron SCT has a focal length of 2,032 mm. When a 30 mm eyepiece is used, the magnification is 68x (2032 ÷ 30 = 67.73). If I then use an 8 mm eyepiece, the power becomes 254x (2032 ÷ 8 = 254). Using our Celestron 8" SCT example we can determine that the focal length is 2,032 mm. This is calculated by multiplying the aperture (8" or 203.2 mm) by the focal ratio (f/10). So, 203.2 x 10 = 2,032.

    Using our 8" SCT example with a 25 mm Antares plossl eyepiece, the eyepiece yields 81x, and its AFOV is 52° (as specified by the manufacturer). The TFOV is then 0.64° or about two-thirds of a degree.
    Magnification: 2032 ÷ 25 = 81.28 or 81x
    AFOV is provided by the manufacturer, or can be calculated in the field using star drift techniques.
    TFOV: 52 ÷ 81.28 = 0.639763779 or 0.64°

    Given the angular velocity of .10976 degrees per second and the total field of view of .64 degrees, this satellite will take 5.8 seconds to cross the field of view.

    However, this is with a magnification of 254X. If you double the magnification it would take around 3 seconds to cross the field of view.

    What's the magnification of your telescope?

  11. #11
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    Quote Originally Posted by ToSeek
    I think it has more to do with how much of Jupiter's sunlight side is facing us than anything else. At opposition, it's full on to us.
    I don't think we get much of phase-effect, it's so far away. My sky atlas showed it at -2.5 May 5, 660Mkm away, and three months later at -2.0 808Mkm away. That's pretty much what you'd expect from the difference in the distance alone.
    Quote Originally Posted by mugaliens
    Most satellites cross the visible sky in about 10 minutes. Let's take a look at one example from Heavens Above happening soon: Resurs 1-4 Rocket 3.3 23:06:03 18° SSE 23:10:08 89° NW 23:15:28 10° NNW

    That's 62 degrees in 9 minutes and 25 seconds, or 9.41 minutes, which comes to an angular velocity of 6.58 degrees per minute, or .10976 degrees per second.
    Why 62 degrees? It's almost the entire sky (18 to almost 90 is about 72, then down to 10 is about another 80 degrees, so 150--maybe about 2 1/2 times as much as 62). So, on average, it'd be going quite a bit faster--and even faster yet nearer the zenith.

  12. #12
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    Mugaliens- I do not remember what the magnification I had at the time was. And I lost the manual to it that has a table for the magnifications.
    Is there a way to figure it out, based on size of the eyepiece and the mirror's diameter (it's a reflector)?

    ToSeek: I thought Jupiter (and other planets beyond Earth's orbit) always displayed a full sun lit face to us?

  13. #13
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    Quote Originally Posted by ToSeek
    I think it has more to do with how much of Jupiter's sunlight side is facing us than anything else. At opposition, it's full on to us.
    All the planets outside of the earth's orbit always present a full disk. The difference in brightness is due to distance, the outer planets being brightest at opposition to the sun, i.e., when the planet rises as the sun sets.

    One other factor affects the brightness of outer planets. When the outer planet is at perihelion - it's closest approach to the sun - while the earth is at aphelion - it's farthest distance away from the sun - both effects due to the fact that all the planets have elliptical orbits - the planet will shine the brightest. This occurance does not happen at every opposition, but when it does the planet will appear the brightest.

    Hope that helps....

  14. #14
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    Quote Originally Posted by Grand_Lunar
    Is there a way to figure it out, based on size of the eyepiece and
    And the focal length of the telescope. Do you know it? With a reflector, it's approx. the length.

  15. #15
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    I generally see at least one satellite through the eyepiece every evening that I use the telescope. There is a LOT of stuff up there, as the field of view is pretty small.

  16. #16
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    Quote Originally Posted by Flying Deuces
    All the planets outside of the earth's orbit always present a full disk.
    Not quite. Mars shows a very significant phase effect when seen near quadrature, appearing a shade less than 90" illuminated. Jupiter's phase efect is correspondingly smaller, but the shading on the lower-sun limb is quite apparent in many images (and in some occultation views of its moons).

  17. #17
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    Quote Originally Posted by ngc3314
    Not quite. Mars shows a very significant phase effect when seen near quadrature, appearing a shade less than 90" illuminated.
    Why a shade less?

    Wait, is that inches?!

  18. #18
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    I do not remember what the magnification I had at the time was. And I lost the manual to it that has a table for the magnifications.
    Is there a way to figure it out, based on size of the eyepiece and the mirror's diameter (it's a reflector)?
    Magnification = Focal Length of Primary (mirror in your case)/ FL of eyepiece
    FL of primary = Diameter of primary x F/ratio

  19. #19
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    Quote Originally Posted by Grand_Lunar
    The object took just over a second to cross the field of view. So, I would venture that it was too slow to be a meteor, too fast to be a plane.

    Space junk now sounds most probable, given how faint it appeared. Or does the brightness depend on other things too, like size and distance from the Earth?.
    But a plane should have a faster angular speed than an object in LEO, shouldn't it?

    Perhaps it depends on the altitude though.

  20. #20
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    Quote Originally Posted by Grand_Lunar
    Two questions:

    Question 1:

    While observing Saturn in my 'scope, a faint point of light streaked across the field. I looked in the sky, but it wasn't visible.
    Has anyone else see such an occurance in their 'scopes?
    I hypothesize it to have been one of three things:
    -A high flying aircraft (but not too likely, since I saw no running lights)
    -A small satillite
    -A tiny meteor (though there was no trail from it)
    What do you, the people, think?
    I have seen all three when looking at Saturn and at other things. With aircraft, I generally either see the body faintly, or a red and/or green light, or a definite rhythmical flashing.

    With a satelite (these are very common) it is usually a steady light, though not always--there are "Irridium flares" when the antenna is positioned just right to get a really bright flash, and some satelites tumble, exposing brighter and dimmer sides to us.

    A meteor is usually faster than either the aircraft or satellite. Sometimes it leaves a trail, but not always. Sometimes it flares pretty bright as it passes.

  21. #21
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    Quote Originally Posted by Grand_Lunar
    ToSeek: I thought Jupiter (and other planets beyond Earth's orbit) always displayed a full sun lit face to us?
    You're right (or very nearly - see someone's comment about Mars). My visualization of the situation was seriously faulty.
    Everything I need to know I learned through Googling.

  22. #22
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    I'll need more data, Kaptain K. I got a number I know to be wrong.
    How do you figure out F/ratio and FL of the eyepiece?

    Maybe someone here might figure it out before I do:

    The primary diameter is 114mm. Something labled "F" is 500mm.

    I used two eyepiece, but forgot which I had on, so I'll state both: one was 20mm diameter. The other is 4mm.

  23. #23
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    Quote Originally Posted by Grand_Lunar
    How do you figure out F/ratio and FL of the eyepiece?

    Maybe someone here might figure it out before I do:

    The primary diameter is 114mm. Something labled "F" is 500mm.

    I used two eyepiece, but forgot which I had on, so I'll state both: one was 20mm diameter. The other is 4mm.
    F/ratio of the telescope is 114/500, or F/4.4, and magnification is 500/20 (25x) and 500/4 (125x). 20mm and 4mm are the FL of the eyepieces, 500mm is the FL of the telescope.

  24. #24
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    I think you got it, hhEb09'1!

    Now that I've seen the numbers, I now recall the manual gave the same. Kudos to you!

    So, I either had 25x or 125x mag. when I saw the culprit. I think it was 25x I had in, because there were several stars in the field when the light went by. It looked too faint to be visible to the unaided eye.

  25. #25
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    Quote Originally Posted by Kaptain K
    Magnification = Focal Length of Primary (mirror in your case)/ FL of eyepiece
    FL of primary = Diameter of primary x F/ratio
    You're absolutely correct, yet it's probably more ... helpful maybe, to think: FL of primary/diameter of primary=the f ratio. Six of one....

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