Equatorial Coordinate System Explained: How Astronomers Navigate the Celestial Sphere | Launch Pad Astronomy | YouTubeToText
YouTube Transcript: Equatorial Coordinate System Explained: How Astronomers Navigate the Celestial Sphere
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let's talk now about a way that we can
define any location in the sky using a
unique set of coordinates to do that
let's first use an analogy we know from
earth that we can take our own rotation
axis and use that to divide the earth
along the equator into northern and
southern hemispheres that also means
that we can now draw parallel lines to
the equator giving us what we call
parallels of latitude so we start at
zero degrees at the equator and we
arrive at 90 degrees north at the North
Pole and 90 degrees south of the South
Pole now in addition to parallels of
latitude measuring north and south we
also want to be able to measure from
east to west so by international
agreement the prime meridian is an
imaginary line that goes through the
North Pole through Greenwich England at
the Royal Observatory all the way down
to the South Pole and then we can simply
measure east or west in terms of
meridians of longitude so for example
here in Baltimore we are at 39 degrees
north latitude 76 degrees west latitude
a southern example would be cerro
paranal and chile that's 24 degrees
south latitude or 70 degrees west and
rome italy is 42 degrees north and 12
degrees east so that places rome at
about the same latitude as boston
massachusetts now that is how we define
every location on earth and we're going
to use an analogous system to define
every location in the heavens so let's
bring our earth inside of the celestial
sphere and will once again extend our
north and south poles to form the north
and south celestial poles we'll extend
the equator to form the celestial
equator and just as we did before with
parallels of latitude we can now draw
parallel lines to the celestial equator
only we refer to these as parallels of
declination so we measure declination as
zero degrees from the equator all the
way up to positive 90 at the North
celestial Pole and then all the way down
to negative 90 at the South celestial
Pole now we cannot simply take our
meridians and apply those to the sky as
well the reason
for that is because the earth is
rotating and therefore the meridians
would need to rotate as well and that
would make such a system fairly useless
to us instead what we'll do is we'll
take the annual path of the Sun the
ecliptic and we'll note the location
that the Sun is on in March when it
arrives at the vernal equinox
since the Earth rotates on its axis once
every 24 hours
this gives us a 24-hour clock face that
we can write on to the celestial equator
so when we draw a parallel lines to this
clock face we then get hours of right
ascension so again think of not so much
as hours of time but think of it instead
as hours on a clock face for example
Rigel in the constellation of Orion has
a right ascension of a little more than
five hours about a quarter of the way on
to the sixth hour circle so that gives
Rigel a right ascension of five hours
and 15 minutes and since it's south of
the celestial equator that gives us a
declination of minus eight degrees and
twelve minutes of Arc remember we can
take a single degree and we can split
that up into 60 minutes of Arc so this
coordinate system since it's based on
the celestial equator we call this the
equatorial coordinate system and it's a
really convenient way for us to define
every single point on the celestial sphere
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