Astro 10/Harpell

Review Sheet for Quiz 1

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Celestial Astronomy

Be able to define the following:

Ecliptic, Solstice, equinox, local meridian, zenith, celestial equator, Celestial Poles, zodiac, retrograde motion, parallax, angular size, altitude, azimuth, conjunction, opposition, constellation, Asterism

Note that a good definition implies an understanding of the physical basis, if any, for these phenomena. It wouldn’t hurt to write out a sentence or two for each term above.

Questions to help you with the terms above:

· What dates do the solstices occur on? The equinoxes? Which one is about to occur?

· What is happening on Earth on those dates in terms of the amount of sunlight, length of the day, and direction that the sun rises and sets?

· When does the sun transit the local meridian at its highest point of the year? At its lowest point?

· What are the constellations of the Zodiac, and why is the Zodiac a wide band centered on the ecliptic (hint: what does the path of the moon have to do with it?)

· The sun and the moon have the same angular size, even though the sun is about 400 times farther away than the moon. How can this be? How much larger is the sun than the moon?

· What is the difference between an Asterism and a constellation?

· What is the angular size of the moon? How does this compare with the angular size of four fingers held at arms length?

· What is the altitude of Polaris here in Livermore? What is its azimuth?

Identifying images

Be able to recognize the following:

• Summer triangle (know at least the constellation Cygnus and the stars Deneb and Vega)
• Sagittarius
• Scorpius
• The Milky Way (know that it is the plane of our galaxy!)
• The Andromeda Galaxy (at least know that it is another big Galaxy like the Milky Way)
• Big Dipper, pointer sisters, and Polaris

Scale models of the Solar System and beyond

• If the sun were the size of a grapefruit (or softball), how large and how far away would the planets be? What about the nearest star besides the sun?
• If the Earth were the size of a classroom globe (one foot in diameter), how far away would the moon be? How large and how far away would the sun be?

Distances and the speed of light

· How far away are the nearest stars other than the sun in A.U.? Light years?

· How long does it take light to get to the Earth from the Sun? The Moon? Jupiter (currently 6 AU away)? Vega (25 light years away)? Deneb (3000 light years away)?

· How long does it take radio signals to get from the Casinni space craft at Saturn (11 AU away) to the Earth?

· When we view anything, we are viewing as it was in the past. Why? How long ago did light leave most of the stars we see in the night sky? When we are viewing an image of the Andromeda Galaxy, how “old” of an image are we seeing?

· If Astronomers in the Andromeda Galaxy, two million light years away, could see objects as small as people on Earth, what would they see if they were viewing the Earth as you read this sentence?

· How far away can we see objects? Is this distance only limited by the size of our telescopes?

· How far back in time is it possible to observe the universe? Was there a beginning of time?

Our Place in the Universe

· Approximately where are we located in the Milky Way Galaxy? How many light years from the center?

· About how many stars does the Galaxy have?

· What is the local group, local supercluster?

· What is our cosmic address?

Speeding through space

• What speed does a point on the equator of the Earth move due to the Earths spin (in feet per sec or kilometers per hour)?
• Are we, here in Livermore, moving faster or slower than people living on the Equator? Explain why.
• How fast is the Earth moving around the sun (in kilometers per second)?
• How long does it take the sun to make a complete orbit of the Milky Way Galaxy?
• Are there any other motions?

Space and time:

1. How long ago did the Universe begin?
2. How long ago was the sun “born”?
3. How long ago did the Earth form?
4. How long ago did the first singled celled organisms evolve?
5. How long ago did multi-cellular organisms evolve?
6. How long ago did the Dinosaurs become extinct?
7. How long ago did Homo sapiens (us!) evolve?
8. When did agriculture begin?
9. When did we learn the Earth orbits the sun and not vice versa?

If the age of the universe was compressed into one day that begins and ends at midnight, when during this day did numbers 2, 7, 8 occur?

Seasons, Astrology, and Precession of the Earth’s axis

· What causes Seasons on Earth?

· Since the Earth’s orbit is slightly eccentric, one hemisphere is closer to the sun than the other during that hemispheres summer. Which hemisphere is it? Does this hemisphere really have hotter summer? Why or why not?

· Some people think that the seasons are due to the Earths orbit being elliptical…be able to give at least one good counter argument for this (i.e. why is this point of view non-sensical?)

· Why does the earth’s spin axis point towards the North celestial pole (Polaris) as it orbits the sun? In other words, why doesn’t it wobble around during each orbit?

· What is the precession of the Earth spin axis? What causes it? How long is the precession period?

· Be able to explain why precession would change the relationship between seasons and dates unless the calendar was changed to account for it

· Why does the precession force calendar makers to choose between linking months with a season, or linking months with the constellation in conjunction with the sun? Be able to draw a sketch to illustrate your answer.

· How is your astrological sign determined by the objects in the sky (i.e. the sun and stars)? Why doesn’t this relationship agree with the signs listed in your newspaper horoscope?

· Would Astrology have a scientific basis of this little problem was “fixed” by adjusting the dates and signs?

Sky watching, retrograde motion and parallax

· Do all the planets exhibit retrograde motion as seen from Earth? How did ancient astronomers account for this motion?

· How can you tell your latitude in the Earth by locating the North Celestial Pole (i.e. the altitude of Polaris)?

· Where would the North Star be if you observed from the North Pole? From the Equator?

· How did Columbus and other navigators find where they were going without the benefit of satellite tracking at sea (GPS)? Where mariners in the southern hemisphere at a disadvantage?

Eclipses: NOT ON QUIZ #1!!

· What causes a lunar eclipse? A solar eclipse?

· Why don’t eclipses occur at least once a month?

· What is the Line of Nodes? How does this line relate to forecasting eclipses?

· Would eclipses be more or less likely if the tilt of the Moon’s orbital plane with the respect the Ecliptic was 0 degrees? 90 degrees?

· Since the Orbit of the moon about the Earth is elliptical, are we more likely to see a total Solar eclipse at Perigee or apogee? Does it also matter whether or not the Earth is at perihelion or aphelion? What types of solar eclipse would occur when the Moon is at apogee, and the Earth is at perihelion?

Useful info (numbers are rounded for convenience):

1. Distance to moon is 30 times the diameter of the Earth.

2. Distance to sun is 400 times the distance to the moon

3. Distance from Sun to Earth is one AU = eight light minutes = 150,000,000 km

4. distance from Sun to Mercury = .4 AU, Venus .7 AU, Mars 1.5 AU

5. Jupiter is 5 AU from sun (how many fingers do most people have on each hand?)

6. One light year is about 65,000 AU. The nearest star is 4 light years away

7. Angular Diameter of Sun = Angular diameter of moon equals ½ degree (30 minutes of arc)

8. Angular diameter of four fingers held together at arms length= 5 degrees.

9. Angular distance from the last pointer star in the big dipper to Polaris = 30 degrees.

10. Deneb is 3000 light years away. Vega is 25 light years away.