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[Music]

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now we've heard about the Australian

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syron so now we're going to hear about

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iic which is the International Center

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for radio astronomy research is that

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right yes that's where I work but that's

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not talking

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about I'll move away so we're going to

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hear about python for astronomers from

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Andrew

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Williams Andrew is an optical astronomer

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who moved from Research into software

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for telescope and instrumentation Auto

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automation he's been working on the

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merchants and Widefield array and

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relocated and related instrumentation

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since 2007 he works for C uni in Perth

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Australia thank you Andrew

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hi I'd like to start by acknowledging

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the N Nation where I work and the uh uh

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B the sorry the IM Nation where this

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photo is taken and the cooland nation

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here I normally work on this guide this

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is a merch and wide field array radio

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telescope out um in the middle of

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nowhere uh but I'm not going to be

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talking about that I'm going to be

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talking about how you can use Python to

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do astronomy astronomy

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calculations uh for non-

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astronomers so glossing over all of the

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scary mats as Lizzie put it started my

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career here uh I actually did a um

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honors and then a PhD building a digital

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camera for this telescope uh it was a

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liquid nitrogen cooled camera to set up

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an automatic search for Supernova uh and

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I was going to hand this around but I

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didn't realize it was going to be in the

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big room this is $10,000 in 1989 money

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of uh CCD chip and analog to digital

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converter for that camera this is the

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actual chip in the camera that I built

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so if you want to geek out about

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obsolete Electronics find me at lunch

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time so that was the first digital photo

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taken in W by digital photo there's some

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caveats like I mean taken by digital

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camera not digitized and not of

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something in the sky through telescope

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that's a 5 and 1/4 in floppy and a

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cardboard box taken using a pinhole

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camera I put a pin in a piece of

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aluminum foil that was the first picture

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out of the to out of the

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camera but first of all I'm going to

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talk about coordinates

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um when we talk about the position of

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things in the sky we usually don't know

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distances so for coordinates we use

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angles from The

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Observer so those angles are the

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direction that need we need to look to

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see that object so we represent a

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position of the Sky by two angles

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describing a point on the inside of an

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imaginary sphere around the

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Observer it's equivalent to latitude and

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longitude we measure positions on Earth

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uh with angles from the center of the

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Earth around uh what's not an imaginary

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sphere well it's not a sphere but around

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the the sphere of the earth coordinate

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frames we need to work out what

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references we're using when we're

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talking about a coordinate called a

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coordinate

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frame so the frame we use for both

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astronomy and for latitude and longitude

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is based on the rotation of the Earth on

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its axis so for longitude the zero point

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is what we call a grenwich Meridian it's

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just an agreed upon point on the earth

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that we call Zero

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longitude and uh that agreed upon point

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was agreed upon fairly late the French

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had a zero longitude line go through

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Paris Observatory and it just happened

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that the the English one out the

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references for latitude of the equator

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in the pole so 0 degrees latitude is on

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the equator minus 90 is a South Pole and

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Plus 90 is a North Pole and we use

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exactly the same system for coordinates

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in the sky so we can refer to what do we

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call Al azth coordinates where azth is

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the compass bearing that you need to

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face in order to look towards the object

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North is 0° uh East is 90° and so on and

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altitude is the angle above the Horizon

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it has a couple of different names

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sometimes altitude is called um

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elevation the elevation angle and

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sometimes to be really different uh

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people talk about the Zenith angle which

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instead of being the angle above the

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Horizon it's the angle from straight

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overhead so you can find coordinates uh

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that are sort of altitude or elevation

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or 90° that which is a zeni angle the

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problem is the Earth is turning and

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moving so if you work out what the

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altitude and ath is for the moon or

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alpha centur or anything else

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it's only true for that location on

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Earth at that instant in time not really

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useful for telling uh putting in a

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catalog to say this is where AA Sor is

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compared to other

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stars so we Define a new coordinate

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system uh using uh Celestial equator

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which is the line in the sky above the

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equator of the earth and the celestial

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poles which is the points in sky above

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the poles of the earth so you can only

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see one of the celestial poles at a time

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unless you're exactly in the equator in

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which case you can see two but they're

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just on the equator in the northern

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hemisphere the north Celestial pole is

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always due north and it's an angle above

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the Horizon roughly equal to a Latitude

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um it would be exactly equal if the

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Earth wasn't a sphere and things weren't

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more

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complicated I said the Earth was a

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sphere rather in Perth the South Cal

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pole is always due south it's at roughly

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32 de above the Horizon and if you look

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at the stars at night all of the stars

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rotate in a circle around that pole so

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if the South cesal Poles over there a

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star might go in a circle like that

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taking 24 hours to go around further

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away they go up and down and above and

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below the Horizon but close to the pole

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they go in

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circles so equatorial coordinates uh

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need a reference frame and just like uh

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longitude we pick an arbitrary point in

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the sky and we call that zero R

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Ascension ra is the equivalent of of

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longitude in the sky uh don't ask me why

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it's called R Ascension historically

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Reasons from hundreds of years

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ago and also for historical reasons it's

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often measured in hours minutes and

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seconds counting around like time zones

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only to the microsc if you want an

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accurate

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coordinate zero point for ra is this

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arbitrary fix point on the sky called

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the first point of Aries it's the point

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where the ecliptic crosses the um the

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celestial

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Equator the declination of a star is the

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angle above or below the celestial

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equator from Plus 90 the north Celestial

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pole the point in the sky right above

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the nor nor pole all the way through to

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minus 90 at the South Cal pole so we've

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got right Ascension which is like

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longitude measured around the clock

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around the the equator and declination

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which is like latitude from- 90 to Plus

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90 the Earth is tilted relative to the

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rest of the solar system relative to the

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sun and the other planets so that

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inclination line is how much the earth

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axis is tilted we've got the north

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Celestial pole directly above the North

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Pole of the earth South Celestial pole

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directly above the South Pole and we

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measure uh R Ascension is one of that

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those thick red arrows and declination

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is the other thick red arrow uh right

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Ascension being the equivalent to

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longitude and declination being

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equivalent to

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Latitude there are some caveats um the

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earth axis is actually drifting on the

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sky uh the Earth imagine a top slowing

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down it kind of does that so the Earth's

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axis is doing that sort of motion that's

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called procession well the procession is

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this motion the mutation is is the

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bouncing up and down as it rotates and

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that happens over thousands of years but

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because the earth axis is actually

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moving in a different direction in the

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sky every year we need to give the

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position as a right attention and a

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declination and some kind of idea of

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where the Earth Anis is pointing at the

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time usually we we talk about j2000

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meaning a coordinate frame using the

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positions on the sky relative to where

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the Earth's axis is pointing at the

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start of the year 2000 in the 1980s they

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often use uh 1950 as a reference instead

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of

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2000 so it's a little bit like measuring

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latitude and longitude if you wanted to

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use the magnetic pole of the earth

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instead of the the true um the

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rotational pole you know the magnetic

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poles are drifting so if you wanted to

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measure longitude and latitude using the

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magnetic poles of the earth you'd have

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to specify where the magnetic pole was

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when you uh defined those

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coordinates modern positions and a

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modern catalog usually What's called the

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icrs frame which uses 2,000 as an

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equinox to refer to where the axis is

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pointing but they Define coordinates as

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seen from the center of the solar system

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not from the earth which makes a

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difference for nearby objects but not so

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much for Far Away objects an alternative

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is the gcrs frame which is also used the

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the 2000 Equinox where the axis was in

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the year 2000 but refers to coordinates

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as seen from the center of the Earth or

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there are modifications uh where you can

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can use coordinates as seen from your

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particular Observatory and that's

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important if you're looking at things

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close in like if you want to look at um

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Mercury it's more useful to define the

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coordinate as seen from the earth and

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not as seen from the center of the solar

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system because your telescopes are on

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earth if you want to represent time this

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is the first real code here uh I'm going

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to talk about the astropy library

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because it's um the most General

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astronomy Library you can find it is

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incredibly accurate incredibly detailed

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and if you read the documentation it

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will dive you straight into curly

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horrible scary maths that you don't need

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to

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know the basic idea is you import a Time

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class you can either ask for the time

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now or you can pass it a Constructor uh

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in a whole range of different formats uh

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it understands a bunch of them without

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you're needing to explain like if you

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just give it a year month day hour

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minute second it'll understand that if

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you give it uh a big number and tell it

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the format is UNIX that's your the Unix

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Tim stamp if you give it a date time

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object it'll also work it out and just

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tell you I put scale equals UTC there

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because there are a bunch of different

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time scales they're all slightly

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different um they all have different uh

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features like some of them are um

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relative to what's called atomic time

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some of them are locked to the rotation

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of the earth if you don't know what a

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time scale is you want UTC if you do

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know what a time scale is you

276
00:10:28,120 --> 00:10:32,880
99.99% of the the time want UTC but the

277
00:10:31,399 --> 00:10:35,200
time class sometimes gives you a

278
00:10:32,880 --> 00:10:36,839
different one if you pass it on usual um

279
00:10:35,200 --> 00:10:38,959
signing value so I'd always say scale

280
00:10:36,839 --> 00:10:41,440
equals UTC there just to be

281
00:10:38,959 --> 00:10:43,800
sure for output there are a whole bunch

282
00:10:41,440 --> 00:10:45,880
of attributes you can ask for the iso

283
00:10:43,800 --> 00:10:48,639
representation if you want a string the

284
00:10:45,880 --> 00:10:51,120
Unix representation if you want a a

285
00:10:48,639 --> 00:10:52,519
Epoch timestamp the mjd if you want the

286
00:10:51,120 --> 00:10:53,680
modified Julian day there's a whole

287
00:10:52,519 --> 00:10:56,240
bunch of different attributes if you

288
00:10:53,680 --> 00:10:56,240
want in different

289
00:10:56,519 --> 00:11:00,880
formats the other cool thing about asrai

290
00:10:59,160 --> 00:11:03,040
is almost all of the constructors of

291
00:11:00,880 --> 00:11:06,440
these objects accept iterables as a

292
00:11:03,040 --> 00:11:10,040
value so if you create a Time object

293
00:11:06,440 --> 00:11:12,480
that has an array of values then you get

294
00:11:10,040 --> 00:11:14,320
a single time object that internally

295
00:11:12,480 --> 00:11:16,519
stores that as a numpy array of all of

296
00:11:14,320 --> 00:11:18,959
the values you passed to it and you can

297
00:11:16,519 --> 00:11:21,079
then use that one time object in

298
00:11:18,959 --> 00:11:23,720
calculations and you'll get back an

299
00:11:21,079 --> 00:11:26,639
array of values one for each item in the

300
00:11:23,720 --> 00:11:28,880
input array that's useful because all of

301
00:11:26,639 --> 00:11:31,800
the hairy calculations are done on the

302
00:11:28,880 --> 00:11:33,600
nump as a whole and all of the hairy

303
00:11:31,800 --> 00:11:35,639
parameters about exactly how that time

304
00:11:33,600 --> 00:11:39,720
is defined stored on the object as a

305
00:11:35,639 --> 00:11:42,639
whole and all it stores is a num

306
00:11:39,720 --> 00:11:45,480
values so if you wanted to represent a

307
00:11:42,639 --> 00:11:49,120
position you ask for a Skyward object

308
00:11:45,480 --> 00:11:50,560
Sky cord is a generic astropy uh class

309
00:11:49,120 --> 00:11:53,279
that represents the coordinates of

310
00:11:50,560 --> 00:11:54,600
things in the sky and just like time

311
00:11:53,279 --> 00:11:58,600
there are a whole bunch of different

312
00:11:54,600 --> 00:11:59,839
ways to specify them uh you can ask for

313
00:11:58,600 --> 00:12:01,680
uh a simple

314
00:11:59,839 --> 00:12:03,800
passing two values and if you just pass

315
00:12:01,680 --> 00:12:06,519
two values it recognizes the first one

316
00:12:03,800 --> 00:12:09,800
is right Ascension and the second one is

317
00:12:06,519 --> 00:12:12,360
declination you uh specify the unit with

318
00:12:09,800 --> 00:12:14,839
this unit argument so here both of those

319
00:12:12,360 --> 00:12:17,639
values the first one and the second one

320
00:12:14,839 --> 00:12:20,000
they're in degrees if you want to pass

321
00:12:17,639 --> 00:12:23,399
an a r Ascension in hours then instead

322
00:12:20,000 --> 00:12:26,839
of passing um degrees as a unit you pass

323
00:12:23,399 --> 00:12:28,519
a tupal and the tupal represents the the

324
00:12:26,839 --> 00:12:30,240
units for the first parameter and the

325
00:12:28,519 --> 00:12:35,079
units for the second parameter so that

326
00:12:30,240 --> 00:12:36,320
is 1.234 hours andus 2634 de for R

327
00:12:35,079 --> 00:12:39,680
ension

328
00:12:36,320 --> 00:12:41,480
declaration for uh C we're specifying

329
00:12:39,680 --> 00:12:43,560
the right exension as what's called a SE

330
00:12:41,480 --> 00:12:47,240
admal value that's just hours minutes

331
00:12:43,560 --> 00:12:50,360
and seconds just like you'd specify time

332
00:12:47,240 --> 00:12:52,839
123456 and you can specify either hours

333
00:12:50,360 --> 00:12:54,639
minute seconds uh or degrees minute

334
00:12:52,839 --> 00:12:58,639
seconds you can specify the degrees

335
00:12:54,639 --> 00:13:01,360
value Asus 32 uh degrees 3 minutes and 4

336
00:12:58,639 --> 00:13:03,680
seconds and by the units we've specified

337
00:13:01,360 --> 00:13:06,839
exactly that it's 12 hours and 34

338
00:13:03,680 --> 00:13:10,199
minutes and not 12° and 34

339
00:13:06,839 --> 00:13:13,480
minutes uh if you pass a third argument

340
00:13:10,199 --> 00:13:15,519
uh without a um a parameter name then

341
00:13:13,480 --> 00:13:17,199
it's the distance and again we've

342
00:13:15,519 --> 00:13:18,639
specified the units for that distance as

343
00:13:17,199 --> 00:13:21,279
light years there's a whole bunch of

344
00:13:18,639 --> 00:13:22,920
different units you can use if you ask

345
00:13:21,279 --> 00:13:26,399
for the attributes you can ask for the

346
00:13:22,920 --> 00:13:29,120
value of uh the RA in degrees if you'd

347
00:13:26,399 --> 00:13:30,560
said a. ra. hour you'd get the value

348
00:13:29,120 --> 00:13:33,920
back in hours as you can see on the

349
00:13:30,560 --> 00:13:35,839
second line they're also internally um

350
00:13:33,920 --> 00:13:39,120
storing this as a cartisian

351
00:13:35,839 --> 00:13:41,639
representation so uh you can ask for the

352
00:13:39,120 --> 00:13:44,240
cartisian value and you'll get your x y

353
00:13:41,639 --> 00:13:46,680
and Zed in light years uh and because

354
00:13:44,240 --> 00:13:49,040
these are ICS coordinates it's inight is

355
00:13:46,680 --> 00:13:50,360
from the center of the solar system if

356
00:13:49,040 --> 00:13:52,680
you don't have a distance for that

357
00:13:50,360 --> 00:13:56,160
coordinate then what you get are an XYZ

358
00:13:52,680 --> 00:14:00,720
value in dimensionless um unit one

359
00:13:56,160 --> 00:14:00,720
radius sphere so it's not as useful

360
00:14:01,839 --> 00:14:05,480
you can also look up objects by name

361
00:14:04,000 --> 00:14:07,800
internally that uses what's called a

362
00:14:05,480 --> 00:14:10,600
sesame website run by research

363
00:14:07,800 --> 00:14:11,800
organization in France uh so you can ask

364
00:14:10,600 --> 00:14:14,680
for the name of a whole bunch of

365
00:14:11,800 --> 00:14:16,639
different objects um in from you know

366
00:14:14,680 --> 00:14:18,240
random catalog names in catalogs of

367
00:14:16,639 --> 00:14:20,759
pulsars through to things like alphas

368
00:14:18,240 --> 00:14:22,399
and T once you created it it behaves

369
00:14:20,759 --> 00:14:23,880
like any other Sky coordinate object so

370
00:14:22,399 --> 00:14:26,160
you're going to ask for the hour or the

371
00:14:23,880 --> 00:14:30,480
the RA in hours or the the declination

372
00:14:26,160 --> 00:14:32,240
degrees or the cartisian representation

373
00:14:30,480 --> 00:14:33,800
uh it does not supply distances if you

374
00:14:32,240 --> 00:14:35,120
ask for the distance of alpha centor you

375
00:14:33,800 --> 00:14:37,000
won't get it you'll need to look it up

376
00:14:35,120 --> 00:14:38,880
in a in a catalog and I'll talk about

377
00:14:37,000 --> 00:14:42,560
that

378
00:14:38,880 --> 00:14:44,759
later so uh for objects inside the solar

379
00:14:42,560 --> 00:14:46,920
system we have get sun to tell you the

380
00:14:44,759 --> 00:14:48,680
position of sun get moon tell you where

381
00:14:46,920 --> 00:14:51,399
the Moon is or get body to tell you

382
00:14:48,680 --> 00:14:53,360
where Jupiter or Europa or uh whatever

383
00:14:51,399 --> 00:14:55,040
other solar system body you want and

384
00:14:53,360 --> 00:14:56,800
these things need time as an argument

385
00:14:55,040 --> 00:14:58,839
because all of these things move around

386
00:14:56,800 --> 00:15:01,880
the position of m42 doesn't move it's a

387
00:14:58,839 --> 00:15:03,959
it's a a Galaxy um well not in human

388
00:15:01,880 --> 00:15:07,440
time scales position of the Moon and Sun

389
00:15:03,959 --> 00:15:09,240
and Europa do move so you create a time

390
00:15:07,440 --> 00:15:12,120
and you ask for the position of the Sun

391
00:15:09,240 --> 00:15:15,639
or the moon or what else you want they

392
00:15:12,120 --> 00:15:17,639
return Sky coed instances but um because

393
00:15:15,639 --> 00:15:19,320
they're almost all used to well all of

394
00:15:17,639 --> 00:15:20,800
these functions are used to return the

395
00:15:19,320 --> 00:15:22,680
position of things inside the solar

396
00:15:20,800 --> 00:15:24,279
system they return the positions

397
00:15:22,680 --> 00:15:26,480
relative to the Center of the Earth not

398
00:15:24,279 --> 00:15:29,199
relative to the center of the sun you

399
00:15:26,480 --> 00:15:32,199
can convert it if you want to convert

400
00:15:29,199 --> 00:15:33,839
gcrs uh coordinate to an ICS then you

401
00:15:32,199 --> 00:15:35,720
can do it just the same way you do for

402
00:15:33,839 --> 00:15:37,680
an Al asth conversion and I'll talk

403
00:15:35,720 --> 00:15:38,959
about that later and that's useful

404
00:15:37,680 --> 00:15:41,120
because if you want to get the cartisian

405
00:15:38,959 --> 00:15:43,440
representation back you can ask for the

406
00:15:41,120 --> 00:15:45,440
coordinates of the Sun Moon Europa any

407
00:15:43,440 --> 00:15:47,800
solar system bodies you want convert

408
00:15:45,440 --> 00:15:49,519
them to ICS and then you the cartisian

409
00:15:47,800 --> 00:15:51,360
coordinates Define where these bodies

410
00:15:49,519 --> 00:15:53,079
are in the solar system if you to you

411
00:15:51,360 --> 00:15:54,240
know plot them in a a game or whatever

412
00:15:53,079 --> 00:15:58,240
else you want to

413
00:15:54,240 --> 00:15:59,279
do you can also get uh the location in

414
00:15:58,240 --> 00:16:04,279
cartisian

415
00:15:59,279 --> 00:16:08,079
with velocity so the um OBS do

416
00:16:04,279 --> 00:16:10,399
geolocation um will tell you that the

417
00:16:08,079 --> 00:16:12,519
distance

418
00:16:10,399 --> 00:16:14,319
uh sorry I was talking about the next

419
00:16:12,519 --> 00:16:17,160
slide so this is the cartisian

420
00:16:14,319 --> 00:16:20,720
coordinates of the Sun as seen from the

421
00:16:17,160 --> 00:16:23,199
earth you can see the distance is 99 358

422
00:16:20,720 --> 00:16:25,920
astronomical units not light

423
00:16:23,199 --> 00:16:27,959
years if you want to do alth conversion

424
00:16:25,920 --> 00:16:29,639
to work at things where appear to be uh

425
00:16:27,959 --> 00:16:30,880
for a particular Observer

426
00:16:29,639 --> 00:16:33,560
you need to create what's called an

427
00:16:30,880 --> 00:16:35,199
earth location uh you can do that either

428
00:16:33,560 --> 00:16:36,560
with a from geodetic call where you give

429
00:16:35,199 --> 00:16:38,959
it a latitude and longitude and a height

430
00:16:36,560 --> 00:16:40,759
above the ground or if it's an

431
00:16:38,959 --> 00:16:42,880
observatory you can just ask a location

432
00:16:40,759 --> 00:16:45,480
of parks for example or

433
00:16:42,880 --> 00:16:48,920
mwa internally they're stor as Earth

434
00:16:45,480 --> 00:16:50,839
centered gcrs coordinates in meters uh

435
00:16:48,920 --> 00:16:52,319
but not including the rotation of the

436
00:16:50,839 --> 00:16:55,360
earth so if you ask for the location of

437
00:16:52,319 --> 00:16:58,600
the mwa you'll get back a fixed set of

438
00:16:55,360 --> 00:17:02,120
numbers in meters um defining where the

439
00:16:58,600 --> 00:17:04,720
m W is and that uses the the computed

440
00:17:02,120 --> 00:17:07,120
geode of the earth not assuming it's a

441
00:17:04,720 --> 00:17:09,319
sphere so you're can ask for the Y value

442
00:17:07,120 --> 00:17:11,799
or the cartisian representation in X Y

443
00:17:09,319 --> 00:17:15,480
and Z

444
00:17:11,799 --> 00:17:18,160
uh you can also ask for the um position

445
00:17:15,480 --> 00:17:22,280
and velocity if you pass it a time that

446
00:17:18,160 --> 00:17:24,919
get gcrs posel uh function um Returns

447
00:17:22,280 --> 00:17:27,679
the position of the the mwa telescope

448
00:17:24,919 --> 00:17:29,520
now and the Velocity in x y and Zed in

449
00:17:27,679 --> 00:17:31,760
m/s

450
00:17:29,520 --> 00:17:33,600
uh which is kind of Handy if you want to

451
00:17:31,760 --> 00:17:36,520
plot the Earth turning or how the Earth

452
00:17:33,600 --> 00:17:38,240
is moving in in time and that's used for

453
00:17:36,520 --> 00:17:39,480
a whole bunch of internal calculations

454
00:17:38,240 --> 00:17:42,120
as

455
00:17:39,480 --> 00:17:44,280
well if you want to transform a

456
00:17:42,120 --> 00:17:47,320
coordinate from where it is in the sky

457
00:17:44,280 --> 00:17:50,280
to where it looks like on the ground uh

458
00:17:47,320 --> 00:17:52,960
you create uh Earth location where

459
00:17:50,280 --> 00:17:56,039
you're observing from you create a time

460
00:17:52,960 --> 00:17:58,240
using the same uh Creator we saw before

461
00:17:56,039 --> 00:18:00,559
you create a position for example a

462
00:17:58,240 --> 00:18:03,240
Galaxy called NGC 2997 that's my

463
00:18:00,559 --> 00:18:06,360
favorite Galaxy um you create a

464
00:18:03,240 --> 00:18:08,720
reference frame called alt as um and

465
00:18:06,360 --> 00:18:12,000
that's in the astropod coordinates um

466
00:18:08,720 --> 00:18:14,960
Library so Al as has two parameters an

467
00:18:12,000 --> 00:18:17,720
observing time which is when you're uh

468
00:18:14,960 --> 00:18:19,559
looking at this object and a location

469
00:18:17,720 --> 00:18:22,400
which is where you're looking at it from

470
00:18:19,559 --> 00:18:26,679
and that coordinate frame encodes all of

471
00:18:22,400 --> 00:18:30,520
the scary MTH to transform positions to

472
00:18:26,679 --> 00:18:32,960
um as seen from mwa at that time and

473
00:18:30,520 --> 00:18:35,280
again your observing time can be an

474
00:18:32,960 --> 00:18:37,919
array of values it can be one time

475
00:18:35,280 --> 00:18:41,000
object with 500 times in it uh your

476
00:18:37,919 --> 00:18:43,840
location can have uh a numpy array of

477
00:18:41,000 --> 00:18:46,640
locations in it uh your Sky coordinate

478
00:18:43,840 --> 00:18:49,400
object can have a numpy array of

479
00:18:46,640 --> 00:18:52,280
positions they don't broadcast well uh

480
00:18:49,400 --> 00:18:54,000
you you could generally have one scaler

481
00:18:52,280 --> 00:18:56,159
and a bunch of arrays if you want to

482
00:18:54,000 --> 00:18:58,080
broadcast that one scaler over all the

483
00:18:56,159 --> 00:19:00,200
array values or you need to make sure

484
00:18:58,080 --> 00:19:03,320
all the array values are of the same

485
00:19:00,200 --> 00:19:06,400
dimensions um so if you have 100 times

486
00:19:03,320 --> 00:19:08,640
on 100 positions you get 100 locations

487
00:19:06,400 --> 00:19:10,919
of that each one position at the

488
00:19:08,640 --> 00:19:14,000
corresponding

489
00:19:10,919 --> 00:19:16,280
time your new object after you've used

490
00:19:14,000 --> 00:19:18,200
this transform two function is also a

491
00:19:16,280 --> 00:19:20,200
sky coed object it represents the same

492
00:19:18,200 --> 00:19:22,559
position on the sky but it has a couple

493
00:19:20,200 --> 00:19:25,799
of extra attributes called alt and as

494
00:19:22,559 --> 00:19:28,159
and those Alton as uh are the altitude

495
00:19:25,799 --> 00:19:29,919
above the Horizon and the the aamus the

496
00:19:28,159 --> 00:19:32,440
compass bearing

497
00:19:29,919 --> 00:19:36,039
now all of these attributes of raas and

498
00:19:32,440 --> 00:19:39,440
decks uh and positions and distances

499
00:19:36,039 --> 00:19:41,840
they're all ASI um dimensioned objects

500
00:19:39,440 --> 00:19:43,640
called Unit objects and that's good if

501
00:19:41,840 --> 00:19:45,679
you want to um make sure you're

502
00:19:43,640 --> 00:19:48,120
extracting the right value if you just

503
00:19:45,679 --> 00:19:49,720
ask for the value of the ra you won't

504
00:19:48,120 --> 00:19:51,360
know immediately whether it's in degrees

505
00:19:49,720 --> 00:19:52,720
or hours if you ask for the value of the

506
00:19:51,360 --> 00:19:54,640
distance you won't know it's whether

507
00:19:52,720 --> 00:19:56,600
it's in meters or astronomical units or

508
00:19:54,640 --> 00:20:01,000
light years so you generally need to ask

509
00:19:56,600 --> 00:20:04,159
for the specific unit that you want so

510
00:20:01,000 --> 00:20:06,880
uh al. deg means you're asking for the

511
00:20:04,159 --> 00:20:11,679
value and degrees of the altitude if you

512
00:20:06,880 --> 00:20:14,840
asked for alt dot um hours you could in

513
00:20:11,679 --> 00:20:16,480
theory convert the altitude hours um you

514
00:20:14,840 --> 00:20:18,400
can use these units objects in your own

515
00:20:16,480 --> 00:20:20,679
calculations if you want to create a

516
00:20:18,400 --> 00:20:24,159
value in um kilograms and another value

517
00:20:20,679 --> 00:20:26,159
in meters and divide one U of these

518
00:20:24,159 --> 00:20:30,520
variables by the other youd need to ask

519
00:20:26,159 --> 00:20:32,520
for the result in um kilog per meter uh

520
00:20:30,520 --> 00:20:33,919
and that makes you sure that your

521
00:20:32,520 --> 00:20:34,960
dimensions are correct when you're doing

522
00:20:33,919 --> 00:20:38,120
your

523
00:20:34,960 --> 00:20:40,640
calculations in other words NGC 2997 as

524
00:20:38,120 --> 00:20:44,360
viewed from the mwa at that time on that

525
00:20:40,640 --> 00:20:46,960
date was 60.7 de above the Horizon and a

526
00:20:44,360 --> 00:20:51,280
little bit south of G

527
00:20:46,960 --> 00:20:54,799
West you can also use Astro query Astro

528
00:20:51,280 --> 00:20:59,440
query is a library it's part of asai

529
00:20:54,799 --> 00:20:59,440
that um lets you import

530
00:21:00,400 --> 00:21:06,200
classes that let you interrogate

531
00:21:02,720 --> 00:21:08,919
websites Vier for example is a website

532
00:21:06,200 --> 00:21:12,840
run again by the same guys that do uh

533
00:21:08,919 --> 00:21:14,919
Sesame uh in France and it has many

534
00:21:12,840 --> 00:21:16,960
hundreds of catalogs and each of those

535
00:21:14,919 --> 00:21:18,799
cataloges has many thousands or

536
00:21:16,960 --> 00:21:21,640
sometimes millions or billions of

537
00:21:18,799 --> 00:21:25,080
objects Vier is just one website the

538
00:21:21,640 --> 00:21:28,760
Astro query Library supports dozens of

539
00:21:25,080 --> 00:21:30,679
websites each one of them has its own um

540
00:21:28,760 --> 00:21:34,080
subl Library as

541
00:21:30,679 --> 00:21:37,480
curvier creates a Vier class to um

542
00:21:34,080 --> 00:21:39,960
explore the Vier website as query.

543
00:21:37,480 --> 00:21:42,000
simbad might have a different CL a

544
00:21:39,960 --> 00:21:44,279
different uh class that explores a

545
00:21:42,000 --> 00:21:46,360
simbad website each of these websites is

546
00:21:44,279 --> 00:21:48,039
run by different organizations they'll

547
00:21:46,360 --> 00:21:50,559
have different types of librar some of

548
00:21:48,039 --> 00:21:52,840
these uh cataloges and libraries return

549
00:21:50,559 --> 00:21:55,039
positions and brightnesses and other

550
00:21:52,840 --> 00:21:58,200
parameters for objects some of them

551
00:21:55,039 --> 00:22:00,240
return images so there's an astro cury

552
00:21:58,200 --> 00:22:02,679
Library that that's you return James web

553
00:22:00,240 --> 00:22:04,760
Space Telescope images of whatever field

554
00:22:02,679 --> 00:22:06,159
you want each of them has a slightly

555
00:22:04,760 --> 00:22:09,120
different interface because each of them

556
00:22:06,159 --> 00:22:11,159
is specific to that website there are

557
00:22:09,120 --> 00:22:13,640
some things that they have in common uh

558
00:22:11,159 --> 00:22:18,400
an SQL like search Syntax for finding

559
00:22:13,640 --> 00:22:18,400
things called um

560
00:22:18,640 --> 00:22:23,520
Astro I can't remember what it's called

561
00:22:20,440 --> 00:22:26,080
anyway SQL like so for visier in

562
00:22:23,520 --> 00:22:27,520
particular we can uh do things like

563
00:22:26,080 --> 00:22:28,919
search for catalogs that might be of

564
00:22:27,520 --> 00:22:31,360
interest you can either do that by going

565
00:22:28,919 --> 00:22:34,159
to the viia website and looking or

566
00:22:31,360 --> 00:22:37,279
there's a a query called find catalogs

567
00:22:34,159 --> 00:22:39,440
let you specify some Search terms and

568
00:22:37,279 --> 00:22:41,559
get a catalog list and that catalog list

569
00:22:39,440 --> 00:22:44,080
if you ask for the catalog name of the

570
00:22:41,559 --> 00:22:46,440
description gives you a string which is

571
00:22:44,080 --> 00:22:47,840
the name and the description which is

572
00:22:46,440 --> 00:22:50,440
just a on line summary of what the

573
00:22:47,840 --> 00:22:52,159
description is now when you actually do

574
00:22:50,440 --> 00:22:56,039
that it returns 10 or 12 different

575
00:22:52,159 --> 00:22:59,480
catalogs one of them is called ja a67

576
00:22:56,039 --> 00:23:02,360
a19 that's the the code for that catalog

577
00:22:59,480 --> 00:23:04,679
called the fifth catalog of nearby stars

578
00:23:02,360 --> 00:23:06,480
and that's got about 6,000 nearby stars

579
00:23:04,679 --> 00:23:10,000
in it it's relatively recent it's got

580
00:23:06,480 --> 00:23:13,480
lots of data it looks like it might be

581
00:23:10,000 --> 00:23:15,320
useful so first of all we say the row

582
00:23:13,480 --> 00:23:18,080
limits are minus one by default viio

583
00:23:15,320 --> 00:23:22,480
will return just a few rows to minimize

584
00:23:18,080 --> 00:23:24,720
um load on their server we ask for um

585
00:23:22,480 --> 00:23:27,679
that particular catalog we get a list of

586
00:23:24,720 --> 00:23:30,159
cataloges with that one entry in it uh

587
00:23:27,679 --> 00:23:33,320
and we can ask for element zero of that

588
00:23:30,159 --> 00:23:36,159
list NSC is now what's called an astropy

589
00:23:33,320 --> 00:23:39,320
table astropy tables are pretty cool

590
00:23:36,159 --> 00:23:41,799
first of all they've got a nice um uh

591
00:23:39,320 --> 00:23:43,880
representation uh we can see that we're

592
00:23:41,799 --> 00:23:46,960
pretty printing it we're skipping over

593
00:23:43,880 --> 00:23:49,919
all of the um col columns that we can't

594
00:23:46,960 --> 00:23:50,840
fit across the width we're summarizing

595
00:23:49,919 --> 00:23:53,679
the

596
00:23:50,840 --> 00:23:55,880
rows uh and it's got a bunch of stuff in

597
00:23:53,679 --> 00:23:57,520
it you usually don't need to lose the

598
00:23:55,880 --> 00:23:58,960
whole catalog many catalogs have

599
00:23:57,520 --> 00:24:00,840
billions of entries

600
00:23:58,960 --> 00:24:03,919
well many catalogs have thousands most

601
00:24:00,840 --> 00:24:06,799
have millions and some have billions so

602
00:24:03,919 --> 00:24:09,799
you use um attribute you use methods on

603
00:24:06,799 --> 00:24:12,520
that visier object uh to filter however

604
00:24:09,799 --> 00:24:14,600
you want you can ask for uh the area of

605
00:24:12,520 --> 00:24:16,840
all records in a given area of sky for

606
00:24:14,600 --> 00:24:18,799
example query region you're asking for

607
00:24:16,840 --> 00:24:22,120
the records in a small region of sky in

608
00:24:18,799 --> 00:24:25,000
this case around m81 you know 10 art

609
00:24:22,120 --> 00:24:27,679
minutes around m81 uh you can also

610
00:24:25,000 --> 00:24:30,480
filter by brightness or any other

611
00:24:27,679 --> 00:24:34,360
parameter want dist um any parameter you

612
00:24:30,480 --> 00:24:38,520
want you can specify in this uh filters

613
00:24:34,360 --> 00:24:41,200
column and you get what a list of table

614
00:24:38,520 --> 00:24:43,000
objects table objects are kind of cool

615
00:24:41,200 --> 00:24:45,559
you can ask for the keys and and

616
00:24:43,000 --> 00:24:48,320
represent it as a dictionary uh so in

617
00:24:45,559 --> 00:24:53,000
this case you've got 31 keys with things

618
00:24:48,320 --> 00:24:55,520
like Parallax and uh ra and deck you can

619
00:24:53,000 --> 00:24:58,919
also index by a row number so the

620
00:24:55,520 --> 00:25:00,960
catalog at entry 5 at r aj200

621
00:24:58,919 --> 00:25:03,360
is exactly the same as the catalog at

622
00:25:00,960 --> 00:25:07,000
r2000 entry number five both of them are

623
00:25:03,360 --> 00:25:08,679
the same you can Google that catalog uh

624
00:25:07,000 --> 00:25:11,520
name or you can search for it on the VIS

625
00:25:08,679 --> 00:25:14,360
site you can see that ra2000 and deck

626
00:25:11,520 --> 00:25:18,360
2000 are the coordinates and plx is the

627
00:25:14,360 --> 00:25:20,080
parallx uh pmra PMD and RV are the the

628
00:25:18,360 --> 00:25:22,000
proper motion how fast it's moving in

629
00:25:20,080 --> 00:25:24,799
the sky and the radio velocity which is

630
00:25:22,000 --> 00:25:26,159
how fast is moving towards us so they

631
00:25:24,799 --> 00:25:28,520
represent

632
00:25:26,159 --> 00:25:31,200
velocities Parallax is the difference in

633
00:25:28,520 --> 00:25:32,600
position of that object as seen from

634
00:25:31,200 --> 00:25:34,520
when the earth is in one side of its

635
00:25:32,600 --> 00:25:36,679
orbit and when it's in the other side of

636
00:25:34,520 --> 00:25:38,520
its orbit if it's nearby the angle

637
00:25:36,679 --> 00:25:40,679
appears to move by a lot if it's far

638
00:25:38,520 --> 00:25:43,799
away the angle doesn't move much at all

639
00:25:40,679 --> 00:25:46,320
one Parc has a parallax of one Arc so we

640
00:25:43,799 --> 00:25:48,159
can create a new aray called distances

641
00:25:46,320 --> 00:25:51,360
which is um

642
00:25:48,159 --> 00:25:55,159
32656 that's the uh light year to par to

643
00:25:51,360 --> 00:25:57,000
paret conversion divided by The Parallax

644
00:25:55,159 --> 00:25:59,880
and then we just create a sky coordinate

645
00:25:57,000 --> 00:26:01,640
object that has an RA value which is a

646
00:25:59,880 --> 00:26:03,399
numpy array of all of the raas in the

647
00:26:01,640 --> 00:26:04,720
table a deck value which is a numpy

648
00:26:03,399 --> 00:26:06,880
array of all the declinations in the

649
00:26:04,720 --> 00:26:08,360
table and a distance value which is all

650
00:26:06,880 --> 00:26:10,840
the distances in the

651
00:26:08,360 --> 00:26:11,960
table and then that Sky coordinate

652
00:26:10,840 --> 00:26:14,120
object you can do whatever you want you

653
00:26:11,960 --> 00:26:17,679
can ask for the cartisian uh attribute

654
00:26:14,120 --> 00:26:20,520
to get those X Y and Z values in uh in

655
00:26:17,679 --> 00:26:22,919
um coordinates in in light years or you

656
00:26:20,520 --> 00:26:24,840
can use transform to Al as to get the

657
00:26:22,919 --> 00:26:27,520
altitude and asouth of them or whatever

658
00:26:24,840 --> 00:26:28,880
else you want if you want to go further

659
00:26:27,520 --> 00:26:31,840
give me an email there's a lot of stuff

660
00:26:28,880 --> 00:26:34,880
I glossed over uh astropy documentation

661
00:26:31,840 --> 00:26:36,480
is very cool but very complicated uh I'd

662
00:26:34,880 --> 00:26:38,440
highly recommend skyfield if you're

663
00:26:36,480 --> 00:26:40,039
using anything inside the solar system

664
00:26:38,440 --> 00:26:41,600
skyfield is written by Brandon rhods

665
00:26:40,039 --> 00:26:45,159
who's been out and done Keynotes here at

666
00:26:41,600 --> 00:26:48,039
as Pon a couple of times astrop plan is

667
00:26:45,159 --> 00:26:50,720
good for planning observations um if

668
00:26:48,039 --> 00:26:53,000
you're actually uh planning a telescope

669
00:26:50,720 --> 00:26:56,360
use so I'd highly recommend those guys

670
00:26:53,000 --> 00:26:56,360
and that's it

671
00:27:01,120 --> 00:27:04,480
awesome thank you very much I really

672
00:27:02,760 --> 00:27:05,559
enjoyed it and I really like astronomy

673
00:27:04,480 --> 00:27:07,919
so that was quite

674
00:27:05,559 --> 00:27:11,720
nice just as a quick thank you we've got

675
00:27:07,919 --> 00:27:14,360
a mug for you y thank you little p on

676
00:27:11,720 --> 00:27:15,880
our you mug so cool yeah thanks a lot

677
00:27:14,360 --> 00:27:18,120
thanks very

678
00:27:15,880 --> 00:27:20,399
much now we're going to have a quick

679
00:27:18,120 --> 00:27:24,120
10minute break and then we've got our

680
00:27:20,399 --> 00:27:24,120
next talk on napari