Astronomy

unit one

The celestial sphere is organized into ____ constellations or sectors.

88

They are used to designate areas of the sky and are agreed upon by the Astronomical Union.

Constellations

Circumpolar

Stars and Constellations that circle closely around Polaris (for us in the Northern Hemisphere) and are therefore visible in the sky all night, every night of the year.

Zodiac Constellations

 Are on the same plane as the sun so they get “lost in the sun” during parts of the year and are visible when opposite the sun. 

Rotation

is on our axis every 24 hours (gives us day and night)

Revolution

is around the sun and takes 365 days (gives us our year

Ecliptic

A circle on the Celestial sphere that represents the sun’s apparent path during the year.

Celestial sphere

kinda like a clear circle surrounding the planets - ideological for organization

Declination and Right Ascension

The coordinates used in the equatorial grid, used to find stars.

Declination

is like latitude, degrees north and south of the celestial equator.

Right Ascension

is like longitude, they are lines east of the zero line.

Latitude and longitude

are terrestrial coordinates that locate objects on the earth. Declination and right ascension are comparable, but on the celestial sphere. Declination is like latitude and right ascension is like longitude.

celestial sphere

is an imaginary globe around the earth, containing all the stars and constellations in a fixed position. Just like cities and countries are fixed on the globe, the stars and constellations are fixed. PLANETS, THE MOON and THE SUN are not fixed.

The Celestial Equator

is an imaginary circle on the celestial sphere, directly above the Earth’s equator, in the celestial sphere. Declination shows points north and south (or + and -) of the celestial equator.

A Light Year

is a unit of measurement for distance. It’s the distance light travels in one year. We often discuss stars in terms of their distance in light years.

The zenith

is the point directly above the viewer’s head.

Heliocentric

refers to the sun-centered system proposed by Copernicus that showed all the planets orbiting the sun.

Geocentric

refers to an earth-centered system proposed by Ptolemy and most ancient astronomers, showing the Universe orbiting the earth.

The circumpolar constellations for us

(at our latitude) are: Ursa Major, Ursa Minor, Camelopardalis (we can’t see it very well), Cassiopeia, Draco and Cepheus.

____ and the _____ are both very close and very reflective, making them bright and easily visible to us on Earth.

Venus and the Moon

POLARIS IS FOUND ON THE TIP OF _______

URSA MINOR

Eratosthenes

 found the angular distance between Alexandria and Syene, using shadows on the summer solstice. It was 7.2 degrees which Is 1/50 of the full circumference of the earth (7.2 is 1/50th of 360). He then measured out the distance between the two cities (or paid someone else to do it) and multiplied by 50.

Your horizon varies depending on where you are on Earth. The Celestial Equator is always in the same location on the celestial sphere, however where you see it differs. ONLY STARS ABOVE THE HORIZON are visible to the viewer.

just good to know

_______ used the telescope to view Jupiter, the Moon and Venus. His findings helped provide strong evidence for the Heliocentric model. He also pioneered the use of the telescope to gain data about our Universe.

Galileo

Ptolemy

was an ancient astronomer who proposed a very complicated geocentric model with epicycles of small circular movements of the planets. Although we know now that the earth is not the center, it was interesting and helpful because it did predict the movement of the planets with some accuracy.

Copernicus

proposed the first heliocentric model of the orbits of the planets, with the sun at the center.