This month's star chart shows the southwestern
sky at 8:00 PM on February 24. The bottom line of the chart is NOT
the horizon, but lies instead at an altitude of about 50 deg - more than
halfway to the zenith.
Jupiter and Saturn continue shining
brightly high in the southwest. Notice the negative magnitude of
Jupiter, and the positive magnitude of Saturn. Which is brighter?
The magnitudes of several stars are also shown. Capella, for
example, nearly overhead, is the fifth brightest star in the sky at 0.2
mag.
As the year progresses, notice that
objects rise in the east about 2 hours earlier each month. Since
the heavens rotate 30 degrees in 2 hours, the progress is close to 30 deg
per month, or about 1 deg per day. This relationship between the
degree and day may have provided the basis for the sexagesimal system of
angular measurements: 360 deg in a full circle, which is also close to
the number of days in a year. The ancient Sumerians developed this
system before decimals were invented, so it was easier to divide the deg
into 60ths than into 100ths, hence the 60 minutes in a degree, and the
60 seconds in a minute. Clever, huh? |
