Full transcript
0:00one of the most important things we
0:01talked about in astronomy is distance we
0:03need to know how far away things are so
0:04we can compare them appropriately for
0:07this course we're mostly going to be
0:09focusing on the idea of the astronomical
0:12unit astronomical unit is defined as the
0:16distance from us to the sun between
0:18Earth and the Sun is defined as one
0:21astronomical unit or the average
0:23distance which is roughly 150 million
0:27kilm that's what we Define as an
0:29astronomical unit and thus we can
0:31describe how far away the other planets
0:33are from the Sun in terms of this
0:34astronomical unit as well so this is the
0:37most common distance we're going to be
0:39looking at in this course because again
0:41we're looking and focusing on our solar
0:43system but in astronomy we also talk
0:46about the idea of a lightyear and this
0:49can be a little confusing a little
0:50misleading but a lightyear is a distance
0:53it's not a time it's a distance and a
0:56lightyear is a how far light travel in
1:00one year the distances we're talking
1:04about in astronomy are so vast we have
1:06to use this kind of measurement light
1:09travels roughly 300 million m/s or
1:13300,000 km a second that's incredibly
1:17fast in fact that means that in 1 second
1:19as it says here light would travel
1:21around Earth over seven times that's how
1:24fast light is but the distances we're
1:27talking about still means that that
1:30light takes time to get to us from them
1:32and we'll talk more about that idea in a
1:34second but let's define a light here I'm
1:37not going to show you the conversion of
1:38how to figure this out if you look at
1:40your textbook it shows you how a
1:41lightyear is calculated but it turns out
1:44it's roughly
1:459.46 trillion kilometers that's how far
1:49light travels in one year it's a very
1:52very big distance than other words but
1:55again it still is useful for us because
1:58the distances we're talking about are so
2:00vast in astronomy things are far far far
2:03far far away in fact even the nearest
2:06star our neighboring star the one
2:09closest to us from not compared to our
2:11son of course but the next closest star
2:13other than our son is 4.2 light years
2:17away which tells you just how far how
2:21big and again that's our neighbor in
2:23essence so other stars are even further
2:26and if we start looking at other
2:27galaxies the distances become truly
2:30astronomical so we have to use a
2:33lightyear as a measurement technique
2:35because these things otherwise the
2:36numbers become meaningless I mean we'd
2:37have these huge huge long drawn out
2:39numbers of many many many
2:43kilometers and actually this gets a
2:46little weird when we start thinking
2:47about these distant objects and talking
2:49about the idea of light years and it's
2:51how far away they are from us well it's
2:57actually like time travel when we when
2:59we're doing astronomy when we're
3:01observing these distance objects we're
3:03actually looking at them as they were in
3:06the past light from our own sun takes
3:08about 8 minutes to get to us that means
3:11we are seeing the Sun as it was 8
3:14minutes ago light comes to us it's
3:16traveled through space it gets to us we
3:18are seeing an older version of our own
3:20Sun theoretically the sun could have
3:22exploded 7 minutes ago and we wouldn't
3:25know yet it'd be a very unpleasant
3:27surprise admittedly but we wouldn't know
3:30yet cuz we're seeing it as it was in the
3:33past and this gets even more insane when
3:35you think about how far away these
3:37objects are again that near neighbor
3:39star we're seeing it as it was over four
3:42years ago and in fact when you start
3:44hearing about the expression When You
3:46Wish Upon a Star you might have heard
3:47the idea that well there's a chance it's
3:49dead it's not the happiest of
3:51Expressions I'll admit but some of the
3:54stars in our own Galaxy when we look at
3:56them they might no longer exist because
3:59we are seeing them as they were the
4:01light took so long to get to us from
4:04them that things have changed we're
4:07seeing them as they were however many
4:09light years away they are if you are
4:12looking at an object a million light
4:14years away you're seeing it as it was a
4:16million years ago in the second part of
4:18the course we actually look at objects
4:20that are billions of light years away so
4:22you're seeing the universe as it was
4:25billions of years ago and that's
4:28actually one of the more exciting and
4:29great things about astronomy because
4:31realistically again we can't study most
4:34objects even watching how a sun would be
4:37formed well it would take millions of
4:39years likely if not longer so we can't
4:43just watch objects or watch things
4:46happen in astronomy it would take too
4:48long we'd die before it was done but if
4:51we look at different distances away from
4:54us we are looking at the universe at
4:56different stages as we look at a Galaxy
4:59say
5:00a billion years ago we're seeing the
5:01universe a billion years ago um and
5:04actually this brings me to one of my
5:06favorite sayings it's or not necessarily
5:09sayings but ideas especially for any of
5:11the Star Wars nerds out there like me
5:13well if Star Wars really did happen a
5:17long time ago in a galaxy far far away
5:20if we can find a telescope and point it
5:22in the right direction we might be able
5:23to watch the entire
5:26thing but let's look at the very end of
5:30this chapter because that's really
5:31everything I wanted to cover in chapter
5:33one I'm going to tell you right now
5:35sections 1.6 to 1.9 are optional that
5:38being said you might get a kick out of
5:40section 1.9 is very short and it talks
5:43about the formation of our universe and
5:46tries to put in terms of a calendar year
5:48and in terms of the sections 1.6 to 1.8
5:51it kind of gives this overview of the
5:55universe now I didn't want to cover that
5:58because again this course really focuses
6:00on our solar system so a lot of the
6:02stuff they reference is things we might
6:03not even cover in this course you might
6:05still find it interesting