(1) From your window you see the Sun pass behind a nearby tall building at 3.15pm. At what time the next day should you look out of the same window to see the Sun move behind the building?

The same time.

What is the name that we call the rotation period of the Earth "relative to the Sun"?

A day. A SOLAR day, to be more specific.

(2) If you note that a particular star crosses the meridian at 9pm one night, what time will the same star cross the meridian the next night?

The same time minus 4 minutes - so, 8.56pm.

What is the name that we call the rotation period of the Earth "relative to the stars"?

A SIDEREAL day ("sidereal" means relating to stars).

(3) What do we call the line that passes through the signs of the zodiac?

The ecliptic.

(4) What celestial object follows this line?

The Sun appears to follow the ecliptic across the sky, relative to the stars.

(5) Why do people talk about "winter constellations" or "fall constellations", etc.?

Because, as the Earth moves around the Sun over the year, the constellations of stars we can see at night (in the direction away from the Sun) will vary. So, the Zodiac constellations can only be seen at particular times of the year - or seasons.

(6a) The Sun is higher in the sky in summer than in the winter. Are shadows longer or shorter in winter?

In winter shadows are longer.

(b) If you are in the southern hemisphere (say, in Australia), in which month of the year is the Sun highest in the sky? Is the Sun to the north or south of the zenith when you are in Australia?

In the southern hemisphere the Sun is highest in the sky around the December 21st solstice. The Sun is to the north of the zenith (unlike the northern hemisphere where the Sun is to the south).

(c) The tilt of the Earth's spin axis has changed over time. When the Earth's tilt was less, say 10¡, how much does the Sun's elevation change over the year?

The current 23.5¡ tilt of the Earth's spin axis causes the Sun's elevation to change by 2 x 23.5 = 47¡. If the axis were less - say 10¡ - then the Sun's elevation would change less over the year - by 2 x 10 = 20¡.

Would you expect the seasonal differences in temperature to be more or less?

Much less.

7) Looking at Figure 1.19, find a constellation that is high in the sky around mid-night in

(a) summer, Scorpio, Sagittarius, Capricorn

(b) winter, Taurus, Gemini, Cancer

(c) spring, Aquarius, Pisces, Aries

(d) fall. Leo, Virgo, LIbra

(8) Review of seasons: Fill in the blanks in the paragraph below using words from the list.

Seasons occur on Earth because Earth's axis of rotation is tilted with respect to the ecliptic plane which causes the ecliptic plane and the celestial equatorto cross at two points. These points are referred to as the vernal and the autumnal equinox. When the sun, in its apparent path around the Earth, is at equinox, the lengths of night and day are equal. These positions mark the beginnings of the seasons spring and fall respectively. On the longest day of the year, the sun is at the summer solstice and reaches its highest point in the sky. On the shortest day of the year, the sun is at the winter solstice and reaches its lowest point in the sky. These two positions mark the beginnings of the seasons of summer and winter.

(9) How would you measure your latitude if you were in Australia?

You would measure the angle between the south celestial pole and the south horizon. This would be the negative latitude.

Would you be able to see Polaris?

No. It would be over the north horizon.

What would you use instead of the North Celestial Pole to aid you in navigating?

The south celestial pole.

Is there a star close to the South Celestial Pole like there is a star near the North Celestial Pole?

Unfortunately not. But the Southern Cross is not so far away.

(10a) What is the longitude of the International Date Line?

Half way around the globe from Greenwich, London - 180¡.

(b) Hawaii is at a longitude of 157¡ . How many hours is Hawaii ahead or behind Boulder?

Boulder is at 105¡, so Hawaii is 52¡ further EAST. This makes Hawaii BEHIND (remember NY leads LA). If the Earth spins 360¡ in 24 hours, then each hour is 15¡. So, Hawaii is 52/15 = 3 1/2 hours behind Boulder. Since we tend to stick to whole hours for time zones ( with some weird exceptions), the Hawaii is 4 time zones away from Boulder.

Model answers to the comprehension questions.