AST101 Chap 2 Summary

7 Pages
103 Views
Unlock Document

Department
Astronomy & Astrophysics
Course
AST101H1
Professor
Michael Reid
Semester
Fall

Description
AST101 Chapter 2 – Discovering the Universe for Yourself 2.1 – Patterns in the Night Sky  Constellation: a region of the sky with well-defined borders; the familiar patterns of stars merely help us locate the constellations  North celestial pole: the point directly over earth’s North Pole  South celestial pole: the point directly over earth’s South Pole  Celestial equator: a projection of the earth’s equator into spaces, making a complete circle around the celestial sphere  Ecliptic: the path the sun follows as it appears to circle around the celestial sphere once each year; it crosses the celestial equator at a 23½° angle, because that is the tilt of the Earth’s axis  The Milky Way in the night sky traces our galaxy’s disk of stars- the galactic plane- as it appears from our location in the outskirts of the galaxy  The dark lanes that run down the center of the milky Way contain the densest clouds, and they appear dark because these clouds obscure our view of stars behind them  these clouds generally prevent us from seeing more than a few thousand light-years into our galaxy’s disk  Local sky: the sky as seen from wherever you happen to be standing  Horizon: the boundary between earth and the sky  Zenith: the point directly overhead  Meridian: an imaginary half circle stretching from the horizon due south, through the zenith, to the horizon due south  We can pinpoint the position of any object in the local sky by stating its direction along the horizon (aka azimuth- degrees clockwise from due north) and its altitude above the horizon  Angular size: the angle an object appears to span in your field of view  Angular distance: the angle that appears to separate a pair of objects in the sky  For more precise astronomical measurements, we subdivide each degree into 60 arcminutes and subdivide each arcminute into 60 arcseconds  We can picture the movement of the sky by imagining the celestial sphere rotating around earth  Stars relatively near the north celestial pole remain perpetually above the horizon, that never rise or set but instead make daily counterclockwise circles around the north celestial pole = circumpolar  Latitude measures north-south positions; it is define to be 0°N at the NP and 90°S at the SP  lines of latitude are circles running parallel to the equator  Longitude measures east-west position  lines of longitude = semicircles extending from the NP to the SP  by international treaty, longitude is defined to be 0° along the prime median  Latitude affects the constellations we see because it affects the locations of the horizon and zenith relative to the celestial sphere  The altitude of the celestial pole in your sky is equal to your latitude  e.g. if you see the north celestial pole at an altitude of 40° above your north horizon, your latitude is 40°N  similarly, if you see the south celestial pole at an altitude of 34° above your south horizon, your latitude is 34°S  Finding the north celestial pole is easy, because it lies very close to the star Polaris (aka the North Star)  In the southern hemisphere, you can find the south celestial pole with the aid of the southern cross  Zodiac: the constellations along the ecliptic  The sun’s apparent location along the ecliptic determines which constellations we see at night 2.2 – The Reason for Seasons  Seasons occur because the tilt of earth’s axis causes sunlight to fall differently on earth at different times of the year o Step 1: - earth’s axis remains pointed in the same direction in space (toward Polaris) throughout the year - as a result, the orientation of the axis relative to the sun changes over the course of each orbit - the Northern Hemisphere is tipped toward the sun in June and away from the sun in December; while the reverse is true for the Southern Hemisphere  this is why the two hemispheres experience opposite seasons o Step 2: - the axis tilt in June causes sunlight to strike the Northern Hemisphere at a steeper angle and the Southern Hemisphere at a shallower angle - the steeper sunlight angle makes it summer in the Northern Hemisphere for 2 reasons:  the steeper angle means more concentrated sunlight, which tends to make it warmer  the steeper angle also means the sun follows a longer and higher path through the sky, giving the Northern Hemisphere more hours of daylight during which it is warmed by the sun - this opposite is true for the Southern Hemisphere at this time: the shallower sunlight angle makes it winter because the sunlight is less concentrated and the sun follows a shorter, lower path through the sky o Step 4: it has become winter for the Northern hemisphere and summer in the Southern Hemisphere o Step 3: in between these two extremes, both hemispheres are illuminated equally in March and September  The seasons on earth are caused only by the axis tilt and not by any change in earth’s distance from the sun Solstices and Equinoxes 
More Less

Related notes for AST101H1

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit