Class Notes (860,572)
CA (521,022)
WLU (18,735)
AS (238)
AS101 (238)

AS101 Lecture 4

6 Pages

Course Code
Patrick Mc Graw

This preview shows pages 1 and half of page 2. Sign up to view the full 6 pages of the document.
Lecture 4 1/16/2013 12:22:00 PM The View from here, Part II Reading: Ch. 2.1-2.3 Recap: mapping the sky:  When we talk about mapping the sky, e are thinking about objects (stars, planets, etc.) as if they were on the surface of an imaginary sphere, the celestial sphere that surrounds the earth.  You can make maps of the celestial sphere much as you can make maps of the earth’s surface.  Astronomers have divided the celestial sphere into 88 constellations with well-defined boundaries.  There are several ways to describe the location of something in the sky. One is by using landmarks and directions. We can also describe in which constellation something is located.  Every star is in one and only one of the 88 constellations  Astronomers distinguish constellations (regions of the celestial sphere) from asterisms, which are patterns or groups of stars, more like landmarks.  A given star may be part of more than one asterism. For example, Rigel is part of the “foot” of Orion and is also part of the Winter Circle.  One of the things a map should tell us about is the distances between places. What do you mean when we talk about distances in the sky or on the celestial sphere? Angular Distance vs. Actual (Physical) Distance:  Stars in a constellation or asterism might not be physically close to each other.  What they have in common is that they lie in approximately the same direction from Earth. Angular Size and Angular Distance:  Since we cannot accurately judge how far objects in the sky are, we CANNOT tell their true size. However, we CAN talk about the angular size of an object or the angular distance between two objects.  Angular size or distance is measured in degrees.  Try to estimate the angular size of an object for yourself o Full circle = 360˚ o 1˚ = 60’ (arcminutes) o 1’ = 60” (arcseconds) Angular Size and Physical Size:  An objects angular size appears smaller if it is farther away. This relationship is very useful for calculating actual distances or size. o Angular size = physical size x 360˚ 2 π x distance.  If you double the distance, you cut the angular size in half.  EXAMPLE: o Jupiter if 4.2 au from Earth at the closest. o 4.2 au x (1.5x10^8km/au)=6.3x10^10 km. o Jupiter’s diameter = 1.4x10^5km o Angular size = physical size x 360˚ o 2 π x distance. o 1.4 x 10^5 km x Some approximate Angular Sizes for Comparison  Width of a finger at arm’s length: 1 degree  Size of moon or sun 0.5 degree  Width of “bowl” f Big Dipper: 10 degrees  Smallest feature most human eyes can distinguish  1arcminute (= 1/60 of a degree).  Jupiter (from earth, now): about 0.8 arcminute  F the sun were only 1 ly away, its angular size would be about 9x10^-6 degrees or 003 arcsecond  We can almost see planets’ sizes with unaided eyes, but stars ar
More Less
Unlock Document
Subscribers Only

Only pages 1 and half of page 2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
Subscribers Only
You're Reading a Preview

Unlock to view full version

Unlock Document
Subscribers Only

Log In


Don't have an account?

Join OneClass

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

Sign up

Join to view


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.