1. Alta High Astronomy Intro: Astronomy A stellar course to be in!

2. Alta High Astronomy What are you looking at? http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html

3. Alta High Astronomy Chapter 1: Charting the Heavens The Foundations of Astronomy

4. Alta High Astronomy What is Astronomy? Astronomy is the study of the Universe where the universe is the totality of all space. Often when we think of astronomy, we look to the heavens and think of the constellations. Constellations are groups of stars which have been given names and that when viewed with some imagination, resemble a known object.

5. Alta High Astronomy Constellations Constellations are the result of the natural human tendency to look for patterns. The stars that make up a constellation are not necessarily close to each other in space, they are simply bright enough to be seen by the naked eye. Constellations usually have a cultural bias, that is that each culture throughout history has assigned a name and a story to the constellations. For example, the constellation which North Americans refer to as the big dipper is know as the wagon or the plough in Europe.

6. Alta High Astronomy Constellations in the Sky: Orion Orion – also know as the hunter is the predominant constellation in the winter sky in the northern hemisphere. Usually located by the three stars in the “belt”

7. Alta High Astronomy Constellations in the Sky: Orion

8. Astersim A distinctive pattern of stars that forms part of one or more constellations Alta High Astronomy

10. Objectives Explain the concept of the celestial sphere Understand and use angular measurements including RA and DEC to locate objects in the sky Describe how celestial objects appear to move in the sky and account for these apparent motions in terms of the actual motions of Earth Understand the types of eclipses and how each occurs Use simple geometry to measure the distances and sizes of faraway objects.

11. Alta High Astronomy Finding Your Way Around the Earth On the Earth we give directions using lines of longitude called meridians These lines begin at 0° (Prime Meridian) and go 180° (International date line) east or west Lines of latitude which are called parallels. These lines begin at the equator (0°) and measure to 90° North or South (North and South Pole)

12. Alta High Astronomy Finding Your Way Around the Earth Red dot is in Galveston, TX Latitude 29° 43’ North Longitude 94º 48’ West

13. Alta High Astronomy Finding Your Way Around the Sky In the Sky, we use a concept called the Celestial Sphere to locate objects. Here we use degrees of Declination (similar to latitude) to tell an object’s position above or below the Celestial Equator Hours of Right Ascension (similar to longitude) to tell its position east or west of the.

14. Alta High Astronomy Measurement in the Sky A circle contains 360° so when an object rotates on its axis (as the earth does) it is said to move through 360° Since the earth rotates once every 24 hours, it rotates 15° per hour. 1 degree = 60’ or 60 arcminutes 1’ = 60” or 60 arcseconds Finally, 1 hour of RA = 15°

15. Alta High Astronomy Motion in the Sky The apparent motion of the stars in the sky (including our own sun) is a result of the earth’s rotation, in combination with its revolution around the sun The time required for the earth to rotate on its axis is known as a solar day However, because the earth also is revolving while it rotates the position of the stars at the end of the solar day is slightly different each night The time required to bring the stars back to the same position as the previous night is known as a sidereal day A solar day is 3.9 minutes longer than a sidereal day Leap Year with its additional day each year, is our attempt to make our calendar match that of the stars

16. Alta High Astronomy The Annual Path of the Sun As the sun travels across the sky during the year it follows a predictable path known as the ecliptic The ecliptic passes through 12 identifiable constellations known as the constellations of the zodiac A branch of pseudoscience which studies the zodiac and its supposed influence on our lives is astrology – which we will not study in this class

17. Alta High Astronomy The Annual Path of the Sun The ecliptic is tilted 23.5° because that is the tilt of the earth with respect to the sun The tilt of the ecliptic is what causes the seasons of the year and explains why the seasons in the northern hemisphere are reversed from those in the south

18. Alta High Astronomy The Seasons The northern most point on the ecliptic is where the winter solstice occurs (Dec 21 – the shortest day of the year) and the southern most point is the summer solstice (June 21 – longest day of the year) In between these points are the two points where the sun crosses the celestial equator, points of equal day and night called equinoxes (September 21 – Autumnal equinox & March 21 – Vernal or Spring equinox)

19. Seasons of the Northern Hemisphere Alta High Astronomy

20. Precession Over the long term, the fact that the earth is tilted with respect to the sun causes a “wobble” known as precession Precession will eventually cause a significant shift in the direction of the north pole of the celestial sphere shifting our “north star” from its current position pointing at Polaris to a new position pointing at Vega

21. Alta High Astronomy The Moon: Our Nearest Neighbor The moon, like the stars goes through a regular cycle of changes These changes are called phases There are eight phases in the cycle

22. Alta High Astronomy Eclipses An eclipse is a blocking of light caused by one celestial object passing into the shadow of another object This occurs when the sun, moon, and earth line up The two types of eclipses are a solar eclipse where the sun is blocked, and a lunar eclipse where the moon is blocked

23. Alta High Astronomy Solar Eclipse A solar eclipse occurs at the new moon when the moon passes between the sun and the earth In a perfect alignment there is a total shadow called the umbra producing a total eclipse In a less than perfect alignment there is a partial shadow called the penumbra producing a partial eclipse

24. Alta High Astronomy Geometry: The Mathematics of Astronomy The ancient astronomers were good mathematicians. Part of the reason the Greeks developed astronomy was to study the stars. The measurement of distances is accomplished by triangulation or the use of a right triangle

25. Alta High Astronomy Triangulation To triangulate a distance to an object you need to know the baseline, or a distance between two point on a straight line opposite the object You also need to know the angle between the baseline and the object or any other angle in the triangle. Of course the last criteria is that the angle between the baseline and the distance you want to measure must be 90°

26. Alta High Astronomy Stellar Parallax Stellar Parallax uses triangulation combined with the apparent shifting of an object when seen from two points to estimate the distance to far away celestial objects Using the diameter of the earth as a baseline, astronomers find the parallax angle by observing the same object from opposite sides of the earth Then using triangulation they estimate the distance to the object.