Astronomy: First Year: Week 3: Wednesday

Professor Sinistra
Wednesday
Gryffindor Time: Midnight
Ravenclaw Time: Midnight
Hufflepuff Time: Midnight
Slytherin Time: Midnight

Tonight we will begin by learning vocabulary. Please get out a quill and some parchment. I will want you to study these words for homework.

Apparent magnitude. The brightness of an astronomical object, as observed on Earth and referred to the appearance of some objects chosen as standards. The scale of magnitudes is defined so that a difference of 5 magnitudes corresponds to a ratio of 100 in observed radiation intensity.

Azimuth. Angle measured clockwise around the horizon, from 0* towards the north, through 90* to the east, 180* to the south, 270* to the west, and to 360* due north.

Circumpolar stars. Stars that are close enough to the celestial pole that they do not rise and set each night but can be seen to move around the pole in a circular path. Latitude of observer determines which stars appear circumpolar.

Constellation. A group of stars that seemed to suggest the shape of some god, person, animal or object. Now a term used to designate a region of the sky. There are 88 constellations.

Declination. Angular distance of an object north or south of the celestial equator, measured in degrees. Thus the north celestial pole has a declination of +90 degrees.

Extragalactic. Beyond the Milky Way galaxy.

Latitude. Coordinate used to measure (in degrees) the angular distance of a point or celestial objects above or below an equator.

Light year. Distance that light travels in 1 year.

Longitude. Coordinate used to specify the position of a point or direction around (or parallel to) an equator.

Magnitude. Scale for describing brightness of a celestial object.

Meridian. Great circle, on the celestial sphere or the Earth, that passes through both north and south poles and an observer’s zenith or location.

Orbit. Path traced out by one object around another.

Rotation. Movement (spin) of a body abut an axis that passes through that body. Distinct from revolution, which is motion in an orbit about some point or other body.

Satellite. Body that revolves in orbit around another body. Planets are satellites of the Sun, the Moon is a satellite of the Earth, and artificial satellites have been sent into orbit around the Earth, Moon, Mars and Venus.

Sidereal. Related to the stars. Thus sidereal day, month, period, year: lengths of time intervals specified by motion of some object relative to the stars, as opposed to apparent lengths of those time intervals that will depend on the Earth’s own movements.

Zenith. Point on the sky directly overhead.

Zodiac. Band on the sky, centered on the ecliptic, and about 18 degrees wide, through which the Sun, Moon and planets appear to move through the course of each year.

Quills away now. I want you go outside and see if you can identify any stars. I'll call you back in when class is over.

Ok, class. Time to come in. For homework, I want you to do several things. First, memorize what each of those words mean. Second, I want you to find out exactly how long a light year is and third, I want you to draw me a chart showing the zenith and the zodiac. That's all. You can go back to your nice warm beds now.


******* Thanks to Heartland for the definitions ********