Hi I’m David Fuller from the “Eyes on
the Sky” video series. Let’s look at Stargazing Basics, starting
with understanding directions in the sky. Most of us are already familiar with the cardinal
directions of north, south, east and west. Those can be further split into 16 sub-directions,
like southwest or south-southwest and south-southeast. But all that really tells us is what direction
we are looking from our location; and at best, really only in areas close to the horizon. Not only that, just as the Sun rises in the
east and sets in the west, the stars in the night sky also rise in the east and set in
the west over the course of the night. So how do we discuss other aspects of the
sky? Let’s start with those cardinal directions
again. If we split the sky exactly in half, from
north to south, we would have a line bisecting those halves. That line is called “The meridian.” This line never moves, because it always divides
the sky from north to south. Now if we locate the exact halfway point of
the meridian, we are looking directly overhead, and that point in the sky is known as the
zenith. So what other “locating features” in the
sky are there? Although we don’t see stars during daytime,
the imaginary line in the sky that the Sun traces as Earth revolves around the Sun is
called the ecliptic. Since the planets in our solar system orbit
our star largely on the same plane as each other, the path of the planets in the sky
closely follows this line of the Sun. This line appears lower in the sky during
the summer, and higher during the winter months. So close to – or sometimes right on – the
ecliptic is where we will always find naked eye and telescopic planets in our solar system. Now keep in mind that the Sun doesn’t actually
rise or set; what is actually happening is the Earth is rotating – we just don’t
feel that rotation, because we humans are just along for the ride. So as Earth spins, imagine if you were standing
at the North Pole, and looked straight overhead (when it was dark). The stars would appear to spin around a circle,
with the axis of that circle at the zenith – the point overhead we talked about earlier. That point in the sky around which the stars
rotate is the celestial pole. Of course, you likely won’t ever see it
like that, because no one lives at the North Pole. So as we move downwards in latitude in the
northern hemisphere, that point in the sky around which the stars rotates will move down
towards the northern horizon. If you’re in the upper latitudes, it will
appear higher; the nearer you are to the equator, the closer that point is to the northern horizon. If you’ve every looked at a globe with latitude
and longitude lines on it, then you can probably imagine pretty easily our next set of markings
in the sky: The celestial sphere. The celestial pole is like a spot on a basketball
where the lines meet, and where a good basketball player can make it spin. To locate objects in the sky, we use coordinates
like on Earth, but instead of latitude and longitude, we projects those lines out into
space as if they were on a transparent sphere surrounding Earth, and these are called Right
Ascension and Declination. Right ascension is easy to remember: Face
north for a moment. If the Sun rises in the east, which side of
your body is that? The right side. So the sun, “ascends” from your right
– or Right Ascension. These are like the longitude lines on Earth,
that start at one pole and run to the other in equal spacings. These are listed in “hours” and “minutes”,
and the Zero “Hour” for Right Ascension begins in Aries the Ram That’s easy enough,
yes? And declination is simply the number of degrees
away from the celestial poles – so the degrees from the celestial pole to the celestial equator
is 90 degrees, just like the degrees from our North Pole to the equator. With me so far? Great! Lets review these: quickly: North, East, South, West never change. The meridian splits the sky into two half
from north to south The Zenith is directly overhead
The ecliptic is the path the Sun takes in the sky, along which the planets large follow
The celestial pole is the spot in the sky around which the stars appear to rotate as
Earth spins The celestial sphere uses similar coordinates
as longitude and latitude, but are called Right Ascension and Declination Not hard at all, right? Okay, right ascension and declination may
take a bit to get used to, but the rest should be pretty straightforward. In the next, I’ll explain how to understand
the difference in brightness between objects in the sky. Thanks for watching; I’m David Fuller. Keep your eyes on the sky and your outdoor
lights aimed down by using dark sky friendly lighting fixtures, so we can all see, what’s
up.
