You can see half the sky. Polaris basically doesn't move. We are at 34 deg N lat. Therefore:
Polaris is 34 deg above the horizon. I know this because it would be at "0" on the equator and 90 at the N pole.
A full 34 deg of sky around polaris is visible every night (and day). Those stars never disappear from view.
That leaves 56 deg of the "northern" celestial sphere that varies in its visibility. It means that there are 34 deg of southern stars which are never visible, and another 56 deg of "southern" celestial sphere which always varies in visibility.
Maximal visibility of the star field is on the equator, then. But it's a quality vs quantity thing, as the most northern and southern stars will always be on the horizon.
The axial tilt of the Earth has nothing to do with any of the above assertions. The tilt affects observations of solar objects and can explain why the duration of night and day varies over longer stretches of time. So the tilt is important only insofar as it governs the length of the night.
There is no place on the Earth where night and day are equal in length for every season. There are places where the variation is minimized (e.g. the equator) but the change can never be erased.
If you look straight up, and imagine a line shooting off into space, and then trace that line over one day, you make a cone. The cone can be thought to have a "night" part and a "day" part who's ratios differ according to the season (summer nights are shortest).
If night and day were equal, then one could see all the stars if one started viewing just after sunset in Jan, and stopped viewing 6 months later in July. That is because 12 hours of night are equal to 6 months - or rather, you can "time travel" into the future if you start viewing later in the night. The midnight sky in Jan looks the same as 11pm sky in Feb.
If you really wanted to see all the stars, you'd be better off starting in the Fall and stopping in the Spring, since the nights are (significantly) longer. There is no need to view all year-round to achieve this goal.
When we get to solar objects (including the sun!) I get a little hazier. Does the sun move at the same rate as the stars? It can't because this is inconsistent with the observation that different stars are overhead at midnight in any particular season. Okay, but does the Sun move faster or slower? What a coincidence that there are 12 months in the year and 12 hours in the night! Remarkable that I've never noticed that before.
Why do astronomy?
Why do astronomy? I mean, the pros do it really well with impossibly expensive equipment, and essentially, there is nothing left to discover right? Well, not so fast...
I just got back from an impromptu meeting of sky watchers. I have to say there is something wonderful about seeing Saturn. And the moon. And the constellations being described by someone who knows what they're talking about! About knowing how the stars move. About knowing how the a part of the world works. There's something about appreciating the beauty of a thing directly, without commentary or intermediary. It's something anyone can do, so it's democratic. It's the wide universe, which is awe-inspiring.
It doesn't make sense that seeing something through a 'scope should be any different than seeing a picture on a computer screen or a magazine, but there is a difference. The images are blurry, often shaky, but there's an analogue quality to it that's really appealing. You *know* the image hasn't been altered in any way, (at least not beyond the optics in the scope).
I feel I was quite lucky tonight to get to see Saturn, it's rings and the Cassini Division, 5 of it's moons, and the shadow of the planet on the rings. Someone claimed to see the "crepe belt" (which is a fuzzy interior ring) but I wasn't convinced (but then again I didn't really know what to look for anyway). I learned that at any point on the earth you can see exactly half the sky. I am at about 34 deg north latitude, and so I can see more of the northern hemisphere's stars, but I can see a big chunk of southern starts, too. I learned that the north star moves only about a degree throughout the year (or the night), and so the proportion of northern and souther sky does not vary over the year (it only varies according to latitude). I learned that the stars follow the sun, from east to west, through the night, and that they start a little later each night - and that this reflects the motion of the earth around the sun. I learned that when you are born an Aries this means that the Sun is in Aries, and so not visible in the night skies. I learned that the planets move in the plane of the ecliptic, which is different from the projection of the earth's equator on the star-field (which is 0 degrees declination). I learned that Beetljuice is Orion's shoulder, Regulus is his knee, and that Sirius is the brightest star in the sky (actually, I might have gotten mixed up on the Orion stuff). Tonight, Saturn was in "front" of Leo.
I still think it's weird that the rotation of the earth would cause the stars to move in exactly the same way as our orbit does. If you imagine the sky as an immense sphere, I suppose the earth's orbit isn't really that big, and can be neglected. What's happening can be understood, I guess, is that if you pick a time of night and you look at a particular spot far away from Polaris, and draw that as a line shooting from the earth. If you time lapse the rotation of the earth, that line will describe an arc on the celestial sphere. The next night, the same thing will happen, but the line will start a bit later. (This would be a perfect flash animation!)
I still don't really understand the motion of the planets, but I'm happy to have discovered some things about the stars. In particular, I'm glad to finally be convinced that its OK to visualize the celestial sphere as a rotating thing around polaris, and that I convinced myself that the orbit of the earth can really be neglected for celestial viewing (I'm sure you can't ignore it for planets!).
Some interesting what if questions: what if you were at a different lat (north pole, equator, south pole)? What if the earth's axial tilt was 0 deg rather than ~23 deg? What if it were 90 deg? What affect does you're altitude have on the visibility of the sky (I was thinking coverage, but I suppose you could also ask in respect to clarity)?
Some questions about the planets: why can we see the inner planets at all? Why doesn't the Sun always get in the way? Is there a constrained band in which they appear or do they appear anywhere? How can planets have phases - as outer planets should always be full and inner planets should always be new! What does gibbous mean anyway?
It's clear that astronomy is one of those hobbies, like baseball, that is a source of endless numbers, facts, and trivia. And like baseball, none of it is truly relevant to one's daily life, but it sure is fun!
I just got back from an impromptu meeting of sky watchers. I have to say there is something wonderful about seeing Saturn. And the moon. And the constellations being described by someone who knows what they're talking about! About knowing how the stars move. About knowing how the a part of the world works. There's something about appreciating the beauty of a thing directly, without commentary or intermediary. It's something anyone can do, so it's democratic. It's the wide universe, which is awe-inspiring.
It doesn't make sense that seeing something through a 'scope should be any different than seeing a picture on a computer screen or a magazine, but there is a difference. The images are blurry, often shaky, but there's an analogue quality to it that's really appealing. You *know* the image hasn't been altered in any way, (at least not beyond the optics in the scope).
I feel I was quite lucky tonight to get to see Saturn, it's rings and the Cassini Division, 5 of it's moons, and the shadow of the planet on the rings. Someone claimed to see the "crepe belt" (which is a fuzzy interior ring) but I wasn't convinced (but then again I didn't really know what to look for anyway). I learned that at any point on the earth you can see exactly half the sky. I am at about 34 deg north latitude, and so I can see more of the northern hemisphere's stars, but I can see a big chunk of southern starts, too. I learned that the north star moves only about a degree throughout the year (or the night), and so the proportion of northern and souther sky does not vary over the year (it only varies according to latitude). I learned that the stars follow the sun, from east to west, through the night, and that they start a little later each night - and that this reflects the motion of the earth around the sun. I learned that when you are born an Aries this means that the Sun is in Aries, and so not visible in the night skies. I learned that the planets move in the plane of the ecliptic, which is different from the projection of the earth's equator on the star-field (which is 0 degrees declination). I learned that Beetljuice is Orion's shoulder, Regulus is his knee, and that Sirius is the brightest star in the sky (actually, I might have gotten mixed up on the Orion stuff). Tonight, Saturn was in "front" of Leo.
I still think it's weird that the rotation of the earth would cause the stars to move in exactly the same way as our orbit does. If you imagine the sky as an immense sphere, I suppose the earth's orbit isn't really that big, and can be neglected. What's happening can be understood, I guess, is that if you pick a time of night and you look at a particular spot far away from Polaris, and draw that as a line shooting from the earth. If you time lapse the rotation of the earth, that line will describe an arc on the celestial sphere. The next night, the same thing will happen, but the line will start a bit later. (This would be a perfect flash animation!)
I still don't really understand the motion of the planets, but I'm happy to have discovered some things about the stars. In particular, I'm glad to finally be convinced that its OK to visualize the celestial sphere as a rotating thing around polaris, and that I convinced myself that the orbit of the earth can really be neglected for celestial viewing (I'm sure you can't ignore it for planets!).
Some interesting what if questions: what if you were at a different lat (north pole, equator, south pole)? What if the earth's axial tilt was 0 deg rather than ~23 deg? What if it were 90 deg? What affect does you're altitude have on the visibility of the sky (I was thinking coverage, but I suppose you could also ask in respect to clarity)?
Some questions about the planets: why can we see the inner planets at all? Why doesn't the Sun always get in the way? Is there a constrained band in which they appear or do they appear anywhere? How can planets have phases - as outer planets should always be full and inner planets should always be new! What does gibbous mean anyway?
It's clear that astronomy is one of those hobbies, like baseball, that is a source of endless numbers, facts, and trivia. And like baseball, none of it is truly relevant to one's daily life, but it sure is fun!
A wonderful short story
It's a very short, simple tail about a man in a hotel room and an unexpected event.
http://news.bbc.co.uk/2/hi/programmes/from_our_own_correspondent/6481487.stm
The randomness of it resonates with me. This is an age where every event has meaning, mostly ominous and heralding 'terrorism'. This is a story of a man who's disorientation never devolves into fear.
http://news.bbc.co.uk/2/hi/programmes/from_our_own_correspondent/6481487.stm
The randomness of it resonates with me. This is an age where every event has meaning, mostly ominous and heralding 'terrorism'. This is a story of a man who's disorientation never devolves into fear.
Blogger atrophy
It's a beautiful night, a bit blustry, but cool rather than cold. A perfect evening to feel the refreshing sea air in your face. Before I go I wanted to blog a little bit. I don't really know if anyone reads this thing (certainly not since I stopped posting) so perhaps it doesn't matter. Certainly the ideas haven't stopped coming, but for some reason I've felt less like writing about it here. Perhaps it's the utter lack of feedback - what's the point sending out shots in the dark? None, unless the point is to have Blogger (Google now) host my personal journal for free.
OTOH blogging is still not 'in my blood'. I think that, like with Flickr, there are aspects of blogging that I still don't get. Like the community aspects. Trading links. Trackbacks. Really, it's all greek (geek?) to me. Kind of like Flickr communities. Part of the reason I think I resist learning this aspect is that it's too close to self-promotion, which fills me with supreme distaste for all kinds of irrational reasons. I am much happier creating a thing, letting the world have it, and then not telling them about it. That's what marketers are for, right?
Another issue, at least with this blog, is that it lacks focus. Categories (a new, quite welcome Blogger feature) would help with this, as presumably people could filter out the stuff they don't want. But I think a blog that's focused on software architecture and Java would be more successful than a random hodgepodge of...whatever. Certainly its worth a shot (and certainly I have plenty to say about software coding and design!)
Peace,
Josh
OTOH blogging is still not 'in my blood'. I think that, like with Flickr, there are aspects of blogging that I still don't get. Like the community aspects. Trading links. Trackbacks. Really, it's all greek (geek?) to me. Kind of like Flickr communities. Part of the reason I think I resist learning this aspect is that it's too close to self-promotion, which fills me with supreme distaste for all kinds of irrational reasons. I am much happier creating a thing, letting the world have it, and then not telling them about it. That's what marketers are for, right?
Another issue, at least with this blog, is that it lacks focus. Categories (a new, quite welcome Blogger feature) would help with this, as presumably people could filter out the stuff they don't want. But I think a blog that's focused on software architecture and Java would be more successful than a random hodgepodge of...whatever. Certainly its worth a shot (and certainly I have plenty to say about software coding and design!)
Peace,
Josh
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