Tuesday, 9 July 2013

25

Finally on to reading the stars, you need to be careful as stars are in motion, they rise and set as the sun and moon do. (but they set in formation.) Although some different costellations rise seperately at differing times, differening dates.

Admittedly the stars do move, however due to how far away they are precise measurements are detected with only the proper equipement. However, for now, the stars are cataloged and mapped out using a system called 'right esension and declination', also known as RA and Dec. RA is the position of a star from east-west in the sky, like longitude and Dec is the position measured in the nourth-south direction, like latitude. Ra is in units of hours, minutes and seconds; Dec is in units of degrees, minutes and seconds of arc. There are ninety degrees for a right angle, sixty minutes of an arc for a degree and sity seconds equals a minute of arc. (known as an "arc minute" or "arc second".)

To understand the system are; the first being the North Celestial Pole is axis of earth that pointing North, the second point being that the South Celestial Pole is where the axis of earth points South, obvious but necessary; also it should be noted that on most star maps the lines of RA and Dec are written on them, RA are semicircles that are based around the center of the earth. (Nearly all maps have these written on them hence you don't need to find them yourself.)

To find the NCP in your garden, face North and look at the altitude of x degrees, where x is your geographic latitude. (Do the same for the SCP, if you live in the South hemisphere.)

NOTE: the sign "is used for seconds of arc not inches.

Star maps are avalible online, or you can buy hard copies of them or even full map books of them, some recommended websites are; skyandtelescope, astronomy, astronomynow, skynews.

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