Objectives:1. Compare and contrast between an asterism and a constellation2. Be able to orientate in the night sky to celestial objects3. Be able to measure distances and sizes of celestial objects

Vocabulary:Asterism

constellationsPlanisphere

celestial spherezenith

MeridianElliptic

Circumpolar starsRight Ascension

DeclinationAngular distance

Angular size

Constellations

Constellation: A recognizable pattern in the night sky.Examples: Orion, Ursa Major, Draco

There are 88 constellations.12 constellations are named after the Zodiac

signs, such Libra, Leo, and Pisces..

Asterism

• Asterism: recognizable patterns in the sky that are not a constellation.

• Such as, Big dipper is an asterism in the constellation Ursa major.

The Summer and Winter Trianglestwo useful asterisms

• Summer Triangle: consists of the 3 stars Deneb, Vega, and Altair.

• Winter Triangle: Consists of the 3 stars Procyon, Betelgeuse, and Sirius.

The Celestial Sphere

• Celestial Sphere: an imaginary sphere that extends out into the blackness of space in which celestial objects appear to be placed.

• The celestial sphere is a useful fiction.

Rotation of the Celestial Sphere

• Since the earth rotates, and carries us west to east, objects in the sky appear to rotate in the other direction, from east to west.

• This the same reason that the sun rises in the East and sets in the west.

Zenith and Meridian

Zenith: the highest point over head, no matter your position on earth.

Meridian: The imaginary great circle that runs through the celestial north and south poles.

Azumith and Altitude

• Azimuth/Right Ascension: the angle or hour that measures the position of an object along the horizon, in the eastern direction. (Toward your right if your facing north)

• Any object on the meridian has an Azimuth of 0 degrees.

• Altitude/Declination: both are measured in how many degrees an object above the horizon.

The Ecliptic

• Since our planetary system (the solar system) was formed from the flattening of an accretion disk all of our planets orbit on the same plane with the sun in the middle.

• The planets of our solar system move across the sky along the ecliptic.

Circumpolar Stars

• Circumpolar Stars: Stars that always stay above the horizon, and are near the northern celestial pole.

Seasonality of the Constellations

• The orbit of the earth around the sun changes the earths location.

• For this reason the constellations change with the season.

Angular Size and Angular Distance

• Angular Size: is the angle an object appears to span in your field of view.

• Angular Distance: is the angle that appears to separate two objects.

Your hands as a measuring tool

• Stretched out pinky to thumb: 25 degrees• Index to pinky finger: 15 degrees• Width of your knuckles: 10 degrees• Three fingers: 5 degrees• Pinky: 1 degree