Chapter 1

Astronomy Today

7th Edition

Chaisson/McMillan

Grab your text book

Charting the Heavens

Day 2

Going to the Stars Road at Logan Pass, Glacier National Park. This picture shows our view of the Milky Way in the night sky.

Celestial Sphere

The celestial sphere:

Stars seem to be on the inner surface of a sphere surrounding the Earth

They aren’t, but they can use two-dimensional spherical coordinates (similar to latitude and longitude) to locate sky objects

Celestial Coordinates

Right Ascension• Like longitude• Use units of time-hours

instead of degrees• 0 hour is the vernal equinox

Declination• Like latitude except use +/-

instead of north and south

Terms related to the Celestial Sphere

Terrestrial System• South Pole• North pole• Equator• Latitude

– 0° at the Equator

• Longitude– 0° at the Prime Meridian

Celestial System• South Celestial Pole• North Celestial Pole• Celestial Equator• Declination

0° at celestial Equator

• Right Ascension– 0 Hours at Vernal Equinox

With your table group, discuss why the celestial sphere is an important Astronomical tool even though it does not truly exist– be ready for cold

calling

Angular Measure: A way to describe the amount of sky a celestial body takes up

• Full circle contains 360° (degrees)

• Each degree contains 60′ (arc-minutes)

• Each arc-minute contains 60′′ (arc-seconds)

• Angular size of an object depends on its actual size and distance from viewer

Read Angular diametersAnd answer the following in your

notebook

1. What is apparent size?2. What happened with the coin demonstration?3. What is the equation used to figure angular diameters

With a partner work on Problems 1 through 6 on the worksheet

Getting an angle on the Sun and Moon

Earth’s Orbital Motion

• Daily cycle, noon to noon, is diurnal—solar day and is based on the sun’s position.

• Stars aren’t in quite the same place 24 hours later, though, due to Earth’s rotation around Sun; when they are once again in the same place, one sidereal day has passed

Earth’s Orbital Motion

Seasonal changes to night sky are due to Earth’s motion around Sun

Earth’s Orbital MotionThe Twelve constellations (some say thirteen) that the Sun moves through during the year are called the zodiac; The view of the night sky changes as Earth moves in its orbit about the Sun. As drawn here, the night side of Earth faces a different set of constellations at different times of the year. The 12 constellations named here make up the astrological zodiac.

Turn to your neighbor and discuss what Astrological sign you have been told you are.

Now let’s took a look at Stellarium to find your corrected astrological sign.• Put your birth date in. Locate the sun, turn on

the constellations so you can see what sign the sun was in on your birth date.

Sun signs

• Are based on which constellation the sun was on the day of your birth• Moon sign: which constellation is

the moon is at the time of your birth

• Most astrological signs are incorrectly shown because they are based on your birth where the sun was during Greek times.

Ophiucus

• The thirteenth zodiac sign• Sun passes through Ophiucus’ foot• November 30-Dec. 18• He is the serpent bearer• also used as the medical symbol

1.4 Earth’s Orbital Motion• Ecliptic is plane of Earth’s path around Sun; at 23.5° to celestial equator

• Northernmost point of path (above celestial equator) is summer solstice; southernmost is winter solstice; points where path crosses celestial equator are vernal and autumnal equinoxes

• Combination of day length and sunlight angle gives seasons

• Time from one vernal equinox to next is tropical year

1.4 Earth’s Orbital Motion

Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years

The Measurement of Distance

Triangulation: Measure baseline and angles, can calculate distance

Parallax: Similar to triangulation, but look at apparent motion of object against distant background from two vantage points

The Measurement of Distance

The Measurement of DistanceMeasuring Earth’s radius:Done by Eratosthenes about 2300 years ago; noticed that when Sun was directly overhead in one city,it was at an angle inAnother due to the earth’s curvature.

Measuring that angle and the distance between the cities gives the radius.

Measuring Distances with Geometry

Converting angular diameter and distance into size