Stardate:04:19:98
Early Morning Planet Hunt
For those people who enjoy getting
up early in the morning, or for those people who are willing to do so,
the southeast horizon this week offers an opportunity to view Uranus and
Neptune before the break of dawn.
First, go out into the dark about 5 am, about
an hour before sunrise, and look to your southeast. The Moon will ruin
any good viewing in this area of the sky Tuesday and Wednesday, so try
to go out viewing Thursday or later. This week's viewing session will be
best appreciated with a telescope, as the objects we will be observing
have too small of an apparent diameter to be easily resolved with binoculars.
Any good quality, small backyard telescope will do.
The first object we will turn our gaze towards
this week is the planet Uranus. Sitting nearly due southeast, Uranus rides
18 1/2 degrees above the horizon. Here, you should find a blue/green disk.
You can always tell a planet from a star by the fact that a planet will
display a disk in the field of a telescope, where a star will only show
a simple dot. Of course, planetary nebulas and galaxies also often show
something resembling as disk, but a planets edges are much more well defined!
Since Uranus has an apparent diameter (distance across as seen from Earth)
of 3.5 minutes of arc (about .06 degrees), we can see that with a telescope
whose field of view is one degree, we would see Uranus stretch across about
6% of the field. A small disk, perhaps, but a disk never the less.
Uranus is the brightest of the planets to be discovered
in modern times. Shining at magnitude 5.8, it may have been sighted thousands
of years ago, from time to time, by wandering bands, staring up at the
stars. In those days, before modern house, street, and car lights, there
may have been seven or eight thousand stars visible on a moonless night,
as opposed to perhaps 5000 today, on a similar night, from the darkest
of country skies. Ancient people in cultures around the world noticed Mercury,
Venus, Mars, Jupiter, and Saturn moving in relation to the background stars,
but every one of them seems to have missed dim, slow moving Uranus. Everyone,
until William Herschel, who first saw it on the night of March 13, 1781,
and mistook it for a comet. Writing, "In examining....stars.....I
perceived one that appeared visibly larger than the rest", Herschel
assured his fame after other astronomers deduced that what he had seen
was, in fact, the first planet discovered in historical times.
Next, head ten degrees to the
south, and raise your telescope another 3.25 degrees above the horizon.
Here you will see, perhaps after a little searching, another disk, much
like Uranus, except smaller, and colored sky blue. This is the planet Neptune.
At magnitude 7.9, Neptune is only about 1/7 as bright as Uranus. Revolving
around the sun once every 165 years, Neptune makes it's home 30 times further
away from the Sun than does the Earth. Neptune was first discovered by
Johanne Galle, who discovered the planet after only 1/2 an hour of searching
(based on calculations sent to him by Urbain Jean Leverrier), on the night
of September 23, 1846. He was not the first person to see Neptune, however.
That honor goes to Galileo himself, who saw the planet on December 24,
1612, and January 28, 1613 and mistook it for a star using his primitive
telescope.
Remember that time is of the essence observing
these planets this week, as the sun will ruin the observing by 5:30.