Midmonth Check-In: August 2021 and Celestial Coordinates

Introduction and Monthly Reminders   

    August has been horrible for stargazers in Utah for the first half of the month!  We have had smoke from California and Oregon blowing into the state, giving us the worst air quality in the world!!  Hopefully the second half of the month will bring clear skies for the Perseid Meteor Shower and for observers to enjoy the opposition of Jupiter and Saturn and all of the other night sky delights.  

    The Perseids peaked on the night of the 12th/morning of the 13th but observers will still be able to see meteors from this shower for the next week or so as the Earth plows through the debris field of comet 109P/Swift-Tuttle.  Saturn has already reached opposition this month, but will still be an excellent target for a telescope.  Remember that Jupiter will reach opposition on the 19th.  Jupiter is always a great target with binoculars and any size of telescope.  Don't forget to look for the Lagoon Nebula and NGC 6530 in the southern Milky Way band and the Ring Nebula (M57) in the Summer Triangle.  If you need help finding these objects, click here to go to my post on how to find these objects! 

Think About This....💡

   

    Locations on Earth can be found using their latitude and longitude coordinates.  For those unfamiliar, latitude are the lines that circle the Earth parallel to the equator while longitude are the lines that connect the North Pole and the South Pole.  For example, Salt Lake City, Utah has the coordinates: 40.7608° N, 111.8910° W.  This means that Salt Lake City is 40.7608° North of the Equator and 111.8910° West from Greenwich, England.  Greenwich is designated as the starting point for longitude.  The North Pole has the coordinates 90° N, 135° W.  Latitude runs between 0° and 90° while latitude runs between 0° and 180°.  In addition, these coordinates can be written in degrees (°), minutes ('), and seconds ('').  Each degree can be subdivided into 60 arcminutes and each minute can be subdivided into 60 arcseconds.  For Salt Lake City, the latitude and longitude would be 40° 45' 31.3236'' N, 111° 52' 34.2588'' W.  Most telescopes that I've used have used this format for the location.  This may sound confusing, but the more you use it, the more familiar it will become!      

    

    Astronomers use a similar system called Celestial Coordinates.  Imagine that the Earth is at the center of a sphere, which we will call the celestial sphere.  The stars, planets, galaxies, and your favorite nebulae all can be found on this sphere.  Their distance from the Earth is irrelevant, only their location on this sphere is important.  Now imagine that Earth's equator is projected on this sphere, which would slice it into two equal halves, like an orange.  This line is called the (surprise!) celestial equator.  Similarly, if a line is drawn straight up from the North Pole or straight down from the South Pole, we get the north celestial pole and south celestial pole, respectively.  So far, all we have is a larger sphere and have relabeled the equator and poles as the celestial equator and poles.  

    Now things start to get a little tricky.  Instead of latitude and longitude, we now have declination and right ascension.  Declination is the celestial latitude and extends from 0° to 90°, just like terrestrial latitude.  Declination is also written in degrees, minutes, and seconds.  One small difference is that instead of writing all the positions as positive, southern latitudes are written with a negative number.  Right ascension is celestial longitude and runs from 0° to 360° instead of 0° to 180° East and 0° to 180° West like terrestrial longitude.  In addition, right ascension is typically measured in hours, minutes, and seconds instead of degrees.  The Earth takes 24 hours to complete one day/night cycle or spin 360° on its axis.  This means the Earth spins 15° per hour!  We need to know where to "start" right ascension like we do with longitude on Earth (Greenwich, England).  This point is known as the First Point of Aries which is the imaginary point in space where the celestial equator and the ecliptic (the path where the Moon, Sun, and planets seem to follow) intersect.  This point is the location of the vernal equinox which occurs in March.  When right ascension and declination were first introduced, this point was in the constellation of Aries.  Today it can be found in Pisces and in about 5 more centuries, it will be in Aquarius.  This location changes due to the wobble of Earth's axis.          

    

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Now get outside and look up!