Transcript

INSTRUCTOR:

For more detailed planning, it's helpful to have a celestial coordinate system. And in astronomy, we use coordinates of right ascension and declination. These work in a similar way to latitude and longitude for defining positions on the surface of the Earth, with the added twist caused by the rotation of the Earth.

So to find a way around, we start again at the north celestial pole. And this is marked by the pole star, Polaris, which is nearby. And here in Teneriffe, we're 28 degrees north. So the north celestial pole in the sky here is 28 degrees above the horizon.

Coming down from the celestial pole 90 degrees, we have the celestial equator. And that sits out in space directly above the Earth's equator. To specify the position of an object north or south of the celestial equator, we use degrees of declination. And these work in exactly the same way as degrees of latitude. So an object that's north of the celestial equator will have positive degrees of declination. An object south of the equator of the coordinates will be negative degrees of declination. So for example, an object that's on the equator, such as the Belt of Orion, would be 0 degrees of declination. An object that's up at the pole would be 90 degrees of declination.

To specify the east and west position relative to the celestial equator is a little bit more tricky because of the rotation of the Earth. So to sort this out, let's remember that the Earth rotates once every 24 hours. So 360 degrees in 24 hours is 15 degrees every hour. So the sky will turn 15 degrees every hour. So we can mark out the celestial equator into 24 equal zones of 15 degrees each. And we call these hours of right ascension. And it makes sense to do it that way, because this helps us with the timing of our objects.

So, two objects that are the same declination and 15 degrees apart east to west, their right ascension coordinates will differ by exactly one hour. And that means that as the Earth turns, those two objects will be in the same position in the sky exactly one hour apart. So these celestial coordinates can also be used for controlling the telescope. So you can programme the telescope with the right ascension and declination coordinate for a given object. And the telescope will then go and track that object.

And in catalogues of celestial objects, such as the Messier objects, you'll always find the right ascension and declination coordinates listed alongside each particular object. So, as you become more familiar with this system, you'll be able to use these in planning your observations with Coast. And you'll also have a much better feel for how objects move across the night sky during the course of an evening and with the seasons.