Grab your text book 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. High overhead on a clear, dark night, we can see a rich band of stars known as the Milky Way—so-called for its resemblance to a milky band of countless stars. All these stars (and more) are part of a much larger system called the Milky Way Galaxy, of which our star, the Sun, is one member. This single exposure, dubbed “the Going to the Stars Road,” was made at night with only the Moon’s light illuminating the terrain on the continental divide at Logan Pass in Glacier National Park, near the Montana/Alberta border. (© Tyler Nordgren)

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 Figure 1-11. Caption: Celestial Sphere. Planet Earth sits fixed at the hub of the celestial sphere, which contains all the stars. This is one of the simplest possible models of the universe, but it doesn’t agree with all the facts that astronomers now know about the universe.

Celestial Coordinates Right Ascension Declination Like longitude Use units of time-hours instead of degrees 0 hour is the vernal equinox Like latitude except use +/- instead of north and south

Terms related to the Celestial Sphere Terrestrial System Celestial System South Pole North pole Equator Latitude 0° at the Equator Longitude 0° at the Prime Meridian 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 diameters And answer the following in your notebook What is apparent size? What happened with the coin demonstration? 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 With a partner work on Problems 1 through 6 on the worksheet

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 Figure 1-13. Caption: Solar and Sidereal Days. A sidereal day is Earth’s true rotation period—the time taken for our planet to return to the same orientation in space relative to the distant stars. A solar day is the time from one noon to the next. The difference in length between the two is easily explained once we understand that Earth revolves around the Sun at the same time as it rotates on its axis. Frames (a) and (b) are one sidereal day apart. During that time, Earth rotates exactly once on its axis and also moves a little in its solar orbit—approximately 1°. Consequently, between noon at point A on one day and noon at the same point the next day, Earth actually rotates through about 361° (frame c), and the solar day exceeds the sidereal day by about 4 minutes. Note that the diagrams are not drawn to scale; the true 1° angle is in reality much smaller than shown here.

Earth’s Orbital Motion Seasonal changes to night sky are due to Earth’s motion around Sun Figure 1-14. Caption: Typical Night Sky. (a) A typical summer sky above the United States. Some prominent stars (labeled in lowercase letters) and constellations (labeled in all capital letters) are shown. (b) A typical winter sky above the United States.

Earth’s Orbital Motion The 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. Figure 1-15. Caption: 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. The arrows indicate the most prominent zodiacal constellations in the night sky at various times of year. For example, in June, when the Sun is “in” Gemini, Sagittarius and Capricornus are visible at night.

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 Figure 1-17. Caption: Seasons. In reality, the Sun’s apparent motion along the ecliptic is a consequence of Earth’s orbital motion around the Sun. The seasons result from the inclination of our planet’s rotation axis with respect to its orbit plane. The summer solstice corresponds to the point on Earth’s orbit where our planet’s North Pole points most nearly toward the Sun. The opposite is true of the winter solstice. The vernal and autumnal equinoxes correspond to the points in Earth’s orbit where our planet’s axis is perpendicular to the line joining Earth and the Sun. The insets show how rays of sunlight striking the ground at an angle (e.g., during northern winter) are spread over a larger area than rays coming nearly straight down (e.g., during northern summer). As a result, the amount of solar heat delivered to a given area of Earth’s surface is greatest when the Sun is high in the sky.

1.4 Earth’s Orbital Motion Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years Figure 1-19a. Caption: Precession. (a) Earth’s axis currently points nearly toward the star Polaris. About 12,000 years from now—almost halfway through one cycle of precession—Earth’s axis will point toward a star called Vega, which will then be the “North Star.” Five thousand years ago, the North Star was a star named Thuban in the constellation Draco.

The Measurement of Distance Triangulation: Measure baseline and angles, can calculate distance Figure 1-28. Caption: Triangulation. Surveyors often use simple geometry and trigonometry to estimate the distance to a faraway object by triangulation. By measuring the angles at A and B and the length of the baseline, the distance can be calculated without the need for direct measurement.

The Measurement of Distance Parallax: Similar to triangulation, but look at apparent motion of object against distant background from two vantage points Figure 1-30. Caption: Parallax. (a) This imaginary triangle extends from Earth to a nearby object in space (such as a planet). The group of stars at the top represents a background field of very distant stars. (b) Hypothetical photographs of the same star field showing the nearby object’s apparent displacement, or shift, relative to the distant undisplaced stars.

The Measurement of Distance Measuring 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 in Another due to the earth’s curvature. Figure 1-32. Caption: Measuring Earth’s Radius. The Sun’s rays strike different parts of Earth’s surface at different angles. The Greek philosopher Eratosthenes realized that the difference was due to Earth’s curvature, enabling him to determine Earth’s radius by using simple geometry. Measuring that angle and the distance between the cities gives the radius.

Measuring Distances with Geometry Converting angular diameter and distance into size Figure: More Precisely 1-2.