Jupiter's moons without optical aid

Cú Giobach

After reading this article from Sky and Telescope I thought I'd start a thread about this, has anyone out there ever seen any of those moons without aid?
Technically it should be possible to see Ganymede or maybe Callisto with the naked eye by blocking out Jupiter.
There is a pole outside my house with loads of "things" sticking out of it that looks perfect for the job so I'll be obsessing over this until I'm successful.
Who's up for a competition?

rccaulfield

Never knew it cud be done tbh! I'll try blocking out Jupiter and see can u i pick anything up, the imagination is a powerful thing though so stay away from Stellarium so uv no idea where they are! Did any pre gallileo civilisations ever hint at knowing they were there in art etc?

Cú Giobach

Never come across anything about it myself, just anecdotal evidence like that mentioned in the S&T article.

stoneill

Perhaps pre-telescope civilisations have observed Jupiter moons before but the connection was not made as the assumption is that the moons were not discovered until the telescope.
It's possible I suppose.
It's easy to imagine a casual observer a few thousand years ago, idly looking up at the sky on a clear night, picking out pictures in the firmamant, holding a blade of grass and by chance obscure Jupiter to reveal some points of light.

Cú Giobach

stoneill wrote: »

Perhaps pre-telescope civilisations have observed Jupiter moons before but the connection was not made as the assumption is that the moons were not discovered until the telescope.
It's possible I suppose.
It's easy to imagine a casual observer a few thousand years ago, idly looking up at the sky on a clear night, picking out pictures in the firmamant, holding a blade of grass and by chance obscure Jupiter to reveal some points of light.

So likely I'd say a certainty.
Until the industrial age the sky was a lot clearer planet wide, with the brighter stars and planets even visible in daylight.
No doubt people saw these moons but because continuous observation would be impossible their regularity of motion wouldn't have been noticed, so nobody would have thought they were something special and were just very dim stars that they just happened to glimpse.

coylemj

Cú Giobach wrote: »

Until the industrial age the sky was a lot clearer planet wide, with the brighter stars and planets even visible in daylight.

You can see Venus and Jupiter in the daytime if you know exactly where to look but that's a bit of a broad statement surely, especially when bituminous coal has been banned in Dublin city for many years now. I don't think the atmosphere is that much more opaque now than 1,000 years ago, especially if you live away from industrial cities. If it was then surely the colour of the Moon during lunar eclipses would have changed over the centuries and I'm not aware that it has.

I'm not aware of any star that can be seen in daylight, now or in the past, excluding supernovae of course.

Cú Giobach

coylemj wrote: »

You can see Venus and Jupiter in the daytime if you know exactly where to look but that's a bit of a broad statement surely, especially when bituminous coal has been banned in Dublin city for many years now. I don't think the atmosphere is that much more opaque now than 1,000 years ago, especially if you live away from industrial cities. If it was then surely the colour of the Moon during lunar eclipses would have changed over the centuries and I'm not aware that it has.

I'm not aware of any star that can be seen in daylight, now or in the past, excluding supernovae of course.

I've seen Venus and Jupiter many times in broad daylight with the naked eye, good buzz.
I got that info from a Sky & Telescope article years ago and it has stuck with me ever since, I don't know if I still have that copy in the attic but if I get the time I'll see if I can find it and see who wrote it.

jumpjack

Cú Giobach wrote: »

I've seen Venus and Jupiter many times in broad daylight with the naked eye, good buzz.
I got that info from a Sky & Telescope article years ago and it has stuck with me ever since, I don't know if I still have that copy in the attic but if I get the time I'll see if I can find it and see who wrote it.

It would be very interesting to have ephemeris of "visible passes" of Venus and Jupiter in broad daylight!! :eek:

Cú Giobach

jumpjack wrote: »

It would be very interesting to have ephemeris of "visible passes" of Venus and Jupiter in broad daylight!! :eek:

I used to get the co-ordinates off magazines, use the setting circles (no go-to) on my scope to get a rough position, then use binos to find the object, then get into line with a tree branch or something to keep position in order to move to the naked eye. It took a fair bit of work but was good fun.
You can get the co-ordinates off Stellarium.

jumpjack

Cú Giobach wrote: »

I used to get the co-ordinates off magazines, use the setting circles (no go-to) on my scope to get a rough position, then use binos to find the object, then get into line with a tree branch or something to keep position in order to move to the naked eye. It took a fair bit of work but was good fun.
You can get the co-ordinates off Stellarium.

I know it is possibile, but it is also complex. Having a program/site which automatically calculates visible passes just like heavens-above.com does for ISS, Iridium and others would be cool.

coylemj

Doesn't the term 'visible pass' refer to a fast moving object in low Earth orbit? If Jupiter or Venus is not too close to the Sun and at a good magnitude then you can see it for several hours on a clear day, even without binos.

It's an interesting exercise, you have to find a spot where you are in the shadow of the sun but with a view of the patch of the (blue) sky where the planet is located, then you have to scan the sky very slowly and hope to spot it.

Cú Giobach

coylemj wrote: »

Doesn't the term 'visible pass' refer to a fast moving object in low Earth orbit? If Jupiter or Venus is not too close to the Sun and at a good magnitude then you can see it for several hours on a clear day, even without binos.

It's an interesting exercise, you have to find a spot where you are in the shadow of the sun but with a view of the patch of the (blue) sky where the planet is located, then you have to scan the sky very slowly and hope to spot it.

Because when scanning a blue sky there is nothing to focus your eyes on I always found it impossible to find even Venus without first getting its position with binos, you end up scanning with your eyes out of focus and this makes it near impossible to find.
It is surprisingly bright when you do spot it though

jumpjack wrote: »

I know it is possibile, but it is also complex. Having a program/site which automatically calculates visible passes just like heavens-above.com does for ISS, Iridium and others would be cool.

With the planets you don't have to do any calculations because they don't move fast, and pass over every day just like the sun or moon, you only have to get their exact (or at least pretty close ) position for the time of day you are looking.
You would need to know how to find objects by their co-ordinates though.

coylemj

Cú Giobach wrote: »

With the planets you don't have to do any calculations because they don't move fast, and pass over just like the sun or moon, you only have to get their exact (or at least pretty close ) position for the time of day you are looking.
You would need to know how to find objects by their co-ordinates though.

+1 Forgot about that, you definitely need a compass so that you're looking in the right direction because unlike at night you won't have any point of reference in the sky given that the planet will need to be a good angular distance from the sun.

Cú Giobach

Because of the way this thread has gone I feel I have to give the obligatory warning.

Warning:
Great care should be taken looking at the sky in daylight with binoculars or a telescope, be very aware of the Sun's position and never ever view it without a filter.

coylemj

Obviously agree 100% with the above but you need to be out of the sun in any event (i.e. in the shadow of a building) when looking for Jupiter or Venus in the daytime, otherwise the glare of the sun will make the task impossible.

jumpjack

Cú Giobach wrote: »

With the planets you don't have to do any calculations because they don't move fast, and pass over every day just like the sun or moon, you only have to get their exact (or at least pretty close ) position for the time of day you are looking.
You would need to know how to find objects by their co-ordinates though.

As I said, it's a simple idea.... but in practice, I don't want to check all days on Celestia when&where which planet will be visibile! Doesn't anybody of you know www.heavens-above.com ?!?

Cú Giobach

coylemj wrote: »

Obviously agree 100% with the above but you need to be out of the sun in any event (i.e. in the shadow of a building) when looking for Jupiter or Venus in the daytime, otherwise the glare of the sun will make the task impossible.

Nope, I've stood in bright summer sunshine doing this, it's what makes it quite interesting. You'll find it's the brightness of the actual sky near the sun (it is more white than blue) that makes it difficult, especially if the planet is (relatively) near the sun and being in shadow doesn't make a difference.
For safety sake it is recommended to stand in shadow, but it's not essential.

Cú Giobach

jumpjack wrote: »

As I said, it's a simple idea.... but in practice, I don't want to check all days on Celestia when&where which planet will be visibile! Doesn't anybody of you know www.heavens-above.com ?!?

If you look out at the night sky at the same time of night over the next few months you will see just how slowly Jupiter is moving, the movement from one day to the next is very slight not discernible unless observing how it moves past nearby stars, week to week a bit more and only over a month will you notice a fairly big movement but you would still have no problem following it. Venus moves faster but once you know where it is you will usually see it for months.
They don't appear and disappear over the course of days, but months.
And as I said, they pass over every single day or night, and would be subsequently visible, if not in the night sky then in the daytime sky, except for the very short time it would be behind (or near) the Sun.
People here would use Heavens Above (myself included) to get timings for transitory events like satellite passings etc.
People would use it to find exact co-ordinates or exact rising and setting times, but not to know if a planet is passing over, that would be like wondering if the sun will rise.
What you want is here, by the way.

coylemj

My Skymap has stopped working on WIndows 7 and technical support is sadly lacking so can someone tell me if there's a website that will give me the exact position of a planet for a given location and date and time?

Heavens Above gives lists with rising and setting times but doesn't seem to have the facility to give the positions in the sky at a given time.

jumpjack

Cú Giobach wrote: »

What you want is here, by the way.

Perfect.
Now I need an app which calculates altitude and azimuth for a given location and time.
There are no constellations visible in daylight, I have no reference, and the only chance to see a planet is knowingg exactly when&where to look at.

If I could find the right formulas, I could write this tiny app by myself, by the way. How many people would like to surprise their friends by finding planets in broa light?

jumpjack

Found formulas:

Inputs:
DEC, RA, LAT, LON, YEAR, MONTH, DAY, HOUR, MINUTE

sin(ALT) = sin(DEC)*sin(LAT)+cos(DEC)*cos(LAT)*cos(HA)
cos(AZ) = (sin(DEC) - sin(ALT)*sin(LAT))/(cos(ALT)*cos(LAT))


HA = LST - RA If HA negative, then add 360 to bring in range 0 to 360; RA must be in degrees.

LST = 100.46 + 0.985647 * jd + long + 15*UT

jd is the days from J2000, including the fraction of
a day
UT is the universal time in decimal hours
long is your longitude in decimal degrees, East positive.

Add or subtract multiples of 360 to bring LST in range 0 to 360
degrees.

jd = HOUR*60+MINUTE + DaysToMonthBegin + DAY - DaysSinceJ2000


To calculate DaysToMonthBegin and DaysSinceJ2000:

Table A                |  Table B
Days to beginning of   |  Days since J2000 to
month                  |  beginning of each year
                       |
Month   Normal   Leap  |  Year   Days    |  Year   Days
        year     year  |                 |
                       |                 |
Jan       0        0   |  1998   -731.5  |   2010  3651.5
Feb      31       31   |  1999   -366.5  |   2011  4016.5
Mar      59       60   |  2000     -1.5  |   2012  4381.5
Apr      90       91   |  2001    364.5  |   2013  4747.5
May     120      121   |  2002    729.5  |   2014  5112.5    
Jun     151      152   |  2003   1094.5  |   2015  5477.5
Jul     181      182   |  2004   1459.5  |   2016  5842.5
Aug     212      213   |  2005   1825.5  |   2017  6208.5
Sep     243      244   |  2006   2190.5  |   2018  6573.5
Oct     273      274   |  2007   2555.5  |   2019  6938.5
Nov     304      305   |  2008   2920.5  |   2020  7303.5
Dec     334      335   |  2009   3286.5  |   2021  7669.5

Source: http://www.stargazing.net/kepler/altaz.html


Do iPhone and Android support Java midlets?!?

Cú Giobach

coylemj wrote: »

My Skymap has stopped working on WIndows 7 and technical support is sadly lacking so can someone tell me if there's a website that will give me the exact position of a planet for a given location and date and time?

Heavens Above gives lists with rising and setting times but doesn't seem to have the facility to give the positions in the sky at a given time.

HA gives the Right asc. and Declination for the time you open the page.
Do you have a scope with setting circles or go-to?
If not then....HA also gives the time of meridian transit, which would be when the planet is due south, for its height above the horizon you would need to know where the ecliptic crosses your meridian.
If you can't view at that specific time, then get its elongation (angular distance from the Sun), get an idea of where the line of the ecliptic is for the time you are looking and measure along it using your hand. A clenched fist at arms length is roughly 10°. I have found Venus using this method.
Here is a rough chart giving the elongation of Venus (from mid 2011 to mid 2012). Today, Venus is 23deg east of the Sun.
If you input your data here you can get more accurate details for all the solar system bodies.
By the way now is not a good time to be trying this, Venus will be at greatest elongation around next march, 20-35 degrees is too close to the sun I would think, I can't remember the closest I spotted it myself. Also the daytime ecliptic path is very low in the sky in winter which makes it not ideal for viewing Venus in daylight, you want the planet to be high in a good blue sky.

cocoshovel

I wonder if I could pick it up with a 15x zoom camera. :pac: