Astronomy 2022 September 26-28

determines color, temperature, luminosity, motion, size, life span, evolution and death

luminosity can be deceiving, the size of an object can be the size of a solar system or be light years across, without knowing this we can’t determine speeds, mass

can’t determine speeds, mass of stars or galaxies, distribution of stars, star clusters, galaxies and nebulae giving us a 3D model of universe

Astronomers need to be able to measure the size of the orbit (a) and circular velocity (p) of the stars

The first astronomer to use trigonometric parallax to determine the distance to a star

uses the apparent movement of an observed object due to the change in the position of the observer, using distance from earth and appearance of foreground star at different times/positions of earth

Nearby stars, or planets, appear to shift back and forth with respect to background stars, due to the motion of the Earth around the sun

size of the apparent shift

One arc minute in one degree, 60 arc seconds in one arc minute, 1 degree=60’=3,600”

parallax second, With a baseline of one AU (93 million miles), a star with a parallax angle of 1 arc second (1”) would be 1 parsec or 3.26 light years away

distance=1/parallax angle (in arc seconds), if you use arc seconds for the parallax angle, the distance unit will be the parsec. D=1/p

closest star with largest parallax

Most recent method used to measure parallax angles

can measure parallax angles to determine distances to stars around 100 pc away

could measure parallel angles to determine distances to stars about 1k pc away

can measure parallax angles to determine distances to stars about 10k pc away

How bright an object really is, how much light energy is being radiated, distance independent, radius and temperature

How bright an object appears from Earth, based on the object’s luminosity and distance

An object’s apparent magnitude at a distance of 10 pc (32.6 light year), inverse square law of brightness B= 1/d^2

The process used by astronomers to measure the magnitudes, brightness, of stars and other celestial objects

use your eyes to compare the magnitude of one star to another

Photographic plates (glass), approximately .001% of the star’s light is recorded

the most accurate, and current, type of photometry uses charge-coupled devices, CCDs. Capable of gathering approximately 98% of the star’s light

First magnitude scale (20 brightest stars) second to sixth magnitude (limit normal seeing)

Difference in 1 magnitude: 2.512x (to the power of the next magnitude, so 2 would be 2.512^2). Difference is 2.512. the smaller the number the brighter it is

1=2.512x, 2=6.3x, 3=16x, 4=40x, 5=100x

c)=10^((m-M+5)/5) with D(pc)=distance in parsecs, m=apparent magnitude and M=absolute magnitude