Introductory Astronomy - Lesson # 2

[rosescarlett]

"Hello Professor." Rose said slightly nervous, people said the Astronomy teacher was a bit strict. But Rose was sure she could manage.

[Kaiia Blackthorn]

Kaiia looked at the girl, noting her nervousness. She frowned slightly. The Scarletts were blood traitors, if she recalled correctly. But she prided herself on not allowing her personal feelings to intrude on her teaching, so her voice was less sharp than it had been with the other students as she said, "If I am correct, you were not part of the class when the last lesson took place, so you are naturally exempt from the punishments. However, I would suggest that you read over the first two chapters and work through the homework questions, so that you are not behind the rest of the class." She noted the girl's textbook, open at the correct page, and said, "If you have found your place, please tell the class the names of the eight main phases of the moon."


ooc: I'll repost the homework questions at the end of the class - along with the next batch of homework... bwahahaha ;-)

[rosescarlett]

"Yes, thank you professor, I'll do that." Rose said, relaxing slightly. "The eight phases of the moon are the new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter and waning crescent."

[Kaiia Blackthorn]

"Very good. Starting from New Moon, as the moon orbits the earth, the moon is waxing - that is, growing. We are able to see progressively more of the illuminated side of the moon, until at Full Moon, we see a complete disc. Then as the moon continues in its orbit, it is referred to as waning - that is, shrinking."

Kaiia, walked back to her desk, and used her wand to conjure images of the sun, earth and moon, which proceeded to revolve through a complete cycle. Leaving the images hanging in the air, Kaiia went on,

"Both solar and lunar eclipses can only take place during certain phases - a solar eclipse is only seen at New Moon, a lunar eclipse occurs only at Full Moon. Who can explain how each type of eclipse occurs?"

[Caeleb Dracus]

"It's line of sight." replied Caeleb, without raising his hand. "A solar eclipse can only occur when the moon is directly between the earth and the sun. It's like playing biliards. The cue ball is the sun. It wants to hit the 8-ball (the earth), but there's another ball (the moon) in the way. The eclipse can occur at no other time, because if it is even slightly to one side of the moon, light will get through."
He explained, as thought talking to a room fulll of 5-year-olds.
"The lunar eclipse is the opposite. It only happens when The Earth is directly between the moon and the sun, shutting off all light from the moon's surface. The shadow of the earth is bigger than the moon's shadow, obviously, so the moon can stay in eclipse for a while. It isn't completelly dark, though, it kind of looks a rusty colour. The light from the earth gets refracted in its atmosphere and relfects onto the moon's surface." he concluded.

[Kaiia Blackthorn]

"An interesting analogy, though an unnecessary one," Kaiia commented dryly. "However your explanation is essentially correct. Solar eclipses can occur only at a New Moon, and lunar eclipses only at a Full Moon." The images still hanging in the air rotated, allowing the students to see how the phenomena occurred. Then Kaiia turned back to the class. "One might imagine, seeing this, that eclipses should occur at every New and Full Moon. Can you explain why this does not happen?"

[isabellapeters]

Bella thought for a moment and then raised her hand, "Does it have something to do with the shadows of the moon professor?" she asked. She didn't fully know where she was going with the idea, but she may as well take a guess.

[Kaiia Blackthorn]

"Shadows are responsible for the eclipses themselves, but are not involved in the lack of eclipses at every Full or New moon."

Kaiia enlarged the images hanging in the air, and set them moving.

"Looking at the relative orbits from above, one might think that the sun, moon and earth are aligned twice a month. However, this does not happen because the moon's orbit is not on exactly the same plane as the earth's." She changed the images so that they could see lines showing the orbits of the earth and the moon



"The plane of the Earth's orbit is called the Ecliptic - here represented by the red line. As you see, the moon's orbit - represented by the grey line - is inclined, or tilted from the ecliptic. The difference is approximately five degrees. For half a lunation the moon is above the ecliptic, then it crosses the ecliptic, and for the next half of the lunation, it is below it. The points at which the moon's orbit crosses the ecliptic is called a node. In order for an eclipse to occur, the moon must cross the ecliptic at Full Moon or New Moon."

She looked around at the class. "Does anyone have any questions about eclipses, before we move on to study the effect of the moon on the Earth's tides?" she asked.


OOC: I'm going to wrap up this class in the next day or two, as I won't be around over the weekend

[Kaiia Blackthorn]

After a long silence, Kaiia was about to continue to the subject of the moon and tides, when she glanced at the clock. It was within a few minutes of the end of the lesson, so she said,
"I see we are out of time, so we will continue with that topic next term. Everyone except Miss Scarlett, please remain in your seats, and start work on the homework you neglected to hand in. In case anyone's copy of the questions was lost - or destroyed, I will display them on the blackboard for your convenience!"

She flicked her wand and the set of questions displayed:

1) What is an Astronomical Unit? (2 points)
2) How many constellations are there? (1 point)
3) what are the two largest constellations? (1 point)
4) describe the system used to label/identify stars within a constellation (2 points)
5) define the following (1 point per definition)
- ‘Grand Design’ spiral galaxy
- Elliptical galaxy
- Irregular galaxy
- Starburst galaxy
- Constellation
- Nebula
- Star cluster
- Comet
- Meteor
6) apart from the sun, which star is the closest to earth? (1 point)
7) list the eight phases of the moon (4 points)

"I will post the homework for today's lesson on the Astronomy Announcement board. Mr Dracus, I will see you in my office now!."

Kaiia turned and walked out, going into her office next door to the classroom.