Planets in daylight

[sevenperforce]

Sunset is fairly late here at this time of year. I was walking around outside at around 8:20 PM local time and it was still quite bright out; the sun had sunk just below the treeline to the west but the sky hadn't yet started to go gray at all...still pale blue.

To my surprise, I was able to see Jupiter just southeast of the zenith, quite clear. It could have been imagination, but it seemed to have both angular size and a faint golden tinge. I have seen planets just after sunset, but never so high or when the sky is still so bright. 

What's the highest magnitude a planet can get, and is Jupiter's angular size ever visible with the naked eye? Was the gold tint just my eyes playing tricks on me, or was it perhaps Rayleigh scattering?

[Superfluous J]

I've seen both Jupiter and Venus in the middle of the day. Wait until they're near the Moon and go outside, find the Moon, and look around.

I don't think Jupiter's disc would ever be discernible to the naked eye, but I'm not willing to do the math to be sure

[SuperFastJellyfish]

39 minutes ago, sevenperforce said:

Sunset is fairly late here at this time of year. I was walking around outside at around 8:20 PM local time and it was still quite bright out; the sun had sunk just below the treeline to the west but the sky hadn't yet started to go gray at all...still pale blue.

To my surprise, I was able to see Jupiter just southeast of the zenith, quite clear. It could have been imagination, but it seemed to have both angular size and a faint golden tinge. I have seen planets just after sunset, but never so high or when the sky is still so bright. 

What's the highest magnitude a planet can get, and is Jupiter's angular size ever visible with the naked eye? Was the gold tint just my eyes playing tricks on me, or was it perhaps Rayleigh scattering?

I doubt you'd be able to make out Jupiter as more than a point of light, but you can definitely see a hint of the 4 Galilean moons on clear nights with your naked eye.

Edited April 29, 2016 by SuperFastJellyfish

[cubinator]

 

Here's a good reference. Jupiter is a little smaller than the ISS, which is just barely too small to see it's shape. Sometimes when the ISS passes directly overhead you can almost tell it has a definite shape, but can't quite discern it. If you have really good vision, you might have a hint that Jupiter or Venus is a little more than a point, but you couldn't quite be able to make out it's shape, I don't think.

[Findthepin1]

1 hour ago, cubinator said:

 

Here's a good reference. Jupiter is a little smaller than the ISS, which is just barely too small to see it's shape. Sometimes when the ISS passes directly overhead you can almost tell it has a definite shape, but can't quite discern it. If you have really good vision, you might have a hint that Jupiter or Venus is a little more than a point, but you couldn't quite be able to make out it's shape, I don't think.

I have seen Venus as a narrow crescent once, IIRC.

[lajoswinkler]

5 hours ago, 5thHorseman said:

I've seen both Jupiter and Venus in the middle of the day. Wait until they're near the Moon and go outside, find the Moon, and look around.

I don't think Jupiter's disc would ever be discernible to the naked eye, but I'm not willing to do the math to be sure

Disc of Venus is discernible, but visible to a handful of people because most of us have at least some obvious degree of astigmatism and/or myopia that makes tiny sources of light (and point ones) look like little stars so it's not possible to see it. Apparent perfect vision is extremely rare.

Jupiter's disc is a bit smaller so I'm not sure but I'd say probably yes. I don't have apparent perfect vision and I still see it's not a simple apparent point of light like stars are.

[Shpaget]

What if we include the atmospheric effects?

It's a rare sight but I have personally seen the Moon rising absolutely huge (larger than my fully spread fingers at arms length, and I don't have tiny hands). It was very pale, but huge nevertheless.

It was out of ordinary, the very next evening and many later evenings around the same time, from the same location the effect was not present, so I'm not attributing it to an illusion.

[cubinator]

5 hours ago, Shpaget said:

What if we include the atmospheric effects?

It's a rare sight but I have personally seen the Moon rising absolutely huge (larger than my fully spread fingers at arms length, and I don't have tiny hands). It was very pale, but huge nevertheless.

It was out of ordinary, the very next evening and many later evenings around the same time, from the same location the effect was not present, so I'm not attributing it to an illusion.

You were probably seeing a halo around the moon, caused by refraction in ice particles in the upper atmosphere. They're about the size you described, but they don't actually form the image of the moon. The moon can be seen in the center of the halo, but maybe there was a cloud obscuring it and you could only see the ring of the halo, causing you to think that the halo was actually the moon itself. I've never heard of the atmosphere turning into a giant telescope, and I'm sure if it ever did that astronomy would benefit from it.

Edited April 29, 2016 by cubinator

[Shpaget]

It may have been 20 years, but I remember it quite well. It was a perfectly clear sky, winter evening, around 9 pm. The image definitely had craters. It was not halo.

[sevenperforce]

12 hours ago, SuperFastJellyfish said:

I doubt you'd be able to make out Jupiter as more than a point of light, but you can definitely see a hint of the 4 Galilean moons on clear nights with your naked eye.

Really? That would be difficult, I think. Once the sky fully darkened, Jupiter's brightness against the black sky caused a strong diffraction pattern that washed out everything within 3 or 4 radii; I can't imagine that I would have ever been able to spot its moons.

The only reason I thought I could see a disc was because the sky was still bright blue and so it prevented image washout.

7 hours ago, Shpaget said:

What if we include the atmospheric effects?

It's a rare sight but I have personally seen the Moon rising absolutely huge (larger than my fully spread fingers at arms length, and I don't have tiny hands). It was very pale, but huge nevertheless.

It was out of ordinary, the very next evening and many later evenings around the same time, from the same location the effect was not present, so I'm not attributing it to an illusion.

Sorry if the question seems rude, but did you actually extend your hand, or is this just based on your recollection?

The effect of the horizon on perspective causes the image you see to be distorted at your focal point, so your brain sees a much larger image (almost like a fisheye effect) than when the moon is directly overhead, even though the image actually entering your eye is the same size. It is not possible for the moon to occupy that much angular distance at the horizon.

[tater]

As I recall, best seeing is a little under half an arcsecond. Usually it's going to be higher, probably approaching an arcsecond. While you might not resolve it naked eye, the usual impression is that there is much less (or even no) twinkle because they are extended objects.

[sevenperforce]

2 hours ago, tater said:

As I recall, best seeing is a little under half an arcsecond. Usually it's going to be higher, probably approaching an arcsecond. While you might not resolve it naked eye, the usual impression is that there is much less (or even no) twinkle because they are extended objects.

Yeah, lack of central twinkle is the most immediate indicator that you're looking at a planet rather than a star.

Still get a shimmering diffraction pattern, though, due to the suture lines in your eyes.

[Shpaget]

4 hours ago, sevenperforce said:

Sorry if the question seems rude, but did you actually extend your hand, or is this just based on your recollection?

Like I said, it was 20-ish years ago, but I think I did exactly that.

[SuperFastJellyfish]

6 hours ago, sevenperforce said:

Really? That would be difficult, I think. Once the sky fully darkened, Jupiter's brightness against the black sky caused a strong diffraction pattern that washed out everything within 3 or 4 radii; I can't imagine that I would have ever been able to spot its moons.

The only reason I thought I could see a disc was because the sky was still bright blue and so it prevented image washout.

Callisto and Ganymede orbit well outside of 3 or 4 radii of Jupiter at their apparent furthest when viewing from Earth.  Maybe that's when I've seen it.

Jupiter's radius:  ~70,000km

Ganymede's periapse:  ~1,070,000km

Callisto's periapse:  ~1,850,000km

Many times have I looked at Jupiter over the years, and have been able to see a pronounced 'line' of light through Jupiter with my naked eye.  Using Stellarium or my telescope/binoculars, I've confirmed that the pronounced line is in the direction of the plane of the moons.  Maybe I'm seeing what I want to see, but there it is.  

Edited April 29, 2016 by SuperFastJellyfish

[sevenperforce]

6 minutes ago, SuperFastJellyfish said:

Callisto and Ganymede orbit well outside of 3 or 4 radii of Jupiter at their apparent furthest when viewing from Earth.  Maybe that's when I've seen it.

Jupiter's radii:  ~70,000km

Ganymede's periapse:  ~1,070,000km

Callisto's periapse:  ~1,850,000km

Many times have I looked at Jupiter over the years, and have been able to see a pronounced 'line' of light through Jupiter with my naked eye.  Using Stellarium or my telescope/binoculars, I've confirmed that the pronounced line is in the direction of the plane of the moons.  Maybe I'm seeing what I want to see, but there it is.  

Wow, I had assumed all this time that the moons were a great deal closer to Jupiter, but apparently I was wrong.

[SuperFastJellyfish]

Recently, I've come across an android app called 'Where is Io'.  It shows the current apparent positions of the moons and projects where they will be all the way out to about 72 hours from the current time using what they call the 'Jovian Spiral'.  It's quick and easy to use for seeing transits and just plain old identification of which moon is which.  I recommend checking it out.

Edited April 29, 2016 by SuperFastJellyfish

[sevenperforce]

Here's that last image, flipped and superimposed:

 

[Wjolcz]

Don't know about the jovian moons, but the last time is saw the ISS I could swear I saw more than one source of light by it. Thought that it might've been the Dragon capsule on it's approach, but then went back home and learnt that the launch was scrubbed. Was probably the solar arrays on the both sides of the station that gave the impression of two dots flying in a formation.

[lajoswinkler]

Galilean satellites would be visible in best conditions if you used something like a distant power pole line to obscure Jupiter itself. The planet is just too bright so it washes them out from sight. 

[YNM]

On 4/29/2016 at 1:55 PM, Shpaget said:

What if we include the atmospheric effects?

It's a rare sight but I have personally seen the Moon rising absolutely huge (larger than my fully spread fingers at arms length, and I don't have tiny hands). It was very pale, but huge nevertheless.

It was out of ordinary, the very next evening and many later evenings around the same time, from the same location the effect was not present, so I'm not attributing it to an illusion.

Huh ? That's not possible. I do see the same effect even when spreading my hands somewhere not to the Moon, but get your pinkie right on it at arms distance and you'll realize that it's tiny.

BTW, the degree reference (pinkie ~1 deg, thumb ~2 deg, three finger 5 deg, fist 10 deg, full span 20 deg) is size-neutral - if you have tiny hands you'll have short arms, if you have large hands you'll have long arms.

On Topic : I've only saw the Moon at the day, never planets. Once through a telescope, quite nice actually.

Edited May 1, 2016 by YNM

[sevenperforce]

On 4/30/2016 at 5:08 PM, Veeltch said:

Don't know about the jovian moons, but the last time is saw the ISS I could swear I saw more than one source of light by it. Thought that it might've been the Dragon capsule on it's approach, but then went back home and learnt that the launch was scrubbed. Was probably the solar arrays on the both sides of the station that gave the impression of two dots flying in a formation.

I forgot to do this for CRS-8, but it would be really cool for someone to figure out when the Dragon and the ISS will both be separately visible to the naked eye. Typically the ISS is only visible once per day at any given point if it is at all, so there would only be a few places where the two dots of light would be clearly visible and separate.

That Dragon is supposed to be departing soon...on the 8th I think?...so maybe we will get lucky.

[sevenperforce]

22 hours ago, YNM said:

On Topic : I've only saw the Moon at the day, never planets. Once through a telescope, quite nice actually.

If you have a clear sky tonight and live anywhere near the Eastern Time Zone, try looking a bit west of the zenith for a faint spot of light around 8 pm. Jupiter should be visible.

[YNM]

1 hour ago, sevenperforce said:

I forgot to do this for CRS-8, but it would be really cool for someone to figure out when the Dragon and the ISS will both be separately visible to the naked eye. Typically the ISS is only visible once per day at any given point if it is at all, so there would only be a few places where the two dots of light would be clearly visible and separate.

That Dragon is supposed to be departing soon...on the 8th I think?...so maybe we will get lucky.

Hmm... I don't think it's possible - assuming a cross section ratio of 1 : 100 for Dragon : ISS then it's easily 5 magnitude fainter. ISS is already over 0, getting someone to see right to mag 6 is very rare in this modern world.

1 hour ago, sevenperforce said:

If you have a clear sky tonight and live anywhere near the Eastern Time Zone, try looking a bit west of the zenith for a faint spot of light around 8 pm. Jupiter should be visible.

Mind you, my location description is pretty accurate

[sevenperforce]

1 hour ago, YNM said:

 

Mind you, my location description is pretty accurate

Ah well. I did not look at that.