S1 #1,2,4,5,7,9,10,11,12,13,17,21,

4. Distinguish among apparent solar time, mean solar time, standard time, daylight saving time, and universal time.

Apparent solar time is the time based on the actual location of the Sun in the sky, while mean solar time is based on making all days 24 hours long. The two differ because of the tilt of Earth's spin access and because Earth moves at different speeds in its orbit as it gets slightly closer to or farther from the Sun, so that the actual length of a day based on the Sun's position in the sky actually varies over the course of the year, with 24 hours as the average. Apparent solar time can be read directly from a sundial, while mean solar time is easier to obtain with mechanical or electronic clocks because all days are the same length. Standard time is the mean solar time over an east-west swath of Earth known as a time zone. Daylight saving time is simply standard time advanced by 1 hour. Universal Time (UT) is the mean solar time for Greenwich, England.

10. Describe the Sun's path through the local sky on the equinoxes and on the solstice for latitude 40°N. Do the same for the North Pole, and equator.

At 40°N latitude, the Sun will rise due east and set due west on the equinoxes. On these days it will cross the meridian at altitude 50° due south. On the summer solstice, the Sun will rise north of due east, cross the meridian at altitude 73.5° due south, and set north of due west. On the winter solstice, the Sun rises south of due east, crosses the meridian at altitude 26.5° due south, and sets south of due west. At the equator on the equinoxes, the Sun will rise due east, pass directly overhead, and set due west. On the summer solstice, the Sun will rise north of due east, cross the meridian at 66.5° to the north and set north of due west. On the winter solstice, the mirror image will occur: The Sun will rise south of due east, cross the meridian at 66.5° altitude to the south, and set south of due west. At the North Pole on the equinoxes, the Sun will skim the horizon, making a circle all around the horizon each day. On the summer solstice, the Sun will circle 23.5° above the horizon all day. On the winter solstice, we would not see the Sun at all. At the South Pole on the equinoxes, the Sun will skim the horizon, making a circle all around the horizon each day. On the summer solstice, the Sun would not appear at all. On the winter solstice, the Sun will circle 23.5° above the horizon all day.

9. Suppose you are at the North Pole. Where is the celestial equator? Where is the north celestial pole? Describe the daily motion of the sky. Do the same for the equator and for the latitude 40°N.

At the North Pole, the north celestial pole is directly overhead and the celestial equator circles the horizon. At the equator, the north celestial pole is on the northern horizon, and the celestial equator runs from due east to due west and through the zenith. At 40° north latitude, the north celestial pole is due north, 40° above the horizon. The celestial equator runs from due east to due west, passing through an altitude of 50° due south.

7. What are declination and right ascension? How are these celestial coordinates similar to latitude and longitude on Earth? How are they different?

Declination and right ascension are the coordinates we use to pinpoint positions on the celestial sphere. These are quite similar to latitude and longitude: Like latitude, declination is zero at the equator and is measured in degrees. But rather than say "north" or "south," we assign declinations positive or negative values. Right ascension is like longitude, except that it is usually measured in hours, minutes, and seconds rather than in degrees.

2. Define opposition, conjunction, and greatest elongation for planets. Explain both for planets closer than Earth to the Sun and for planets farther than Earth from the Sun.

Opposition:The point at which a planet appears opposite the Sun in our sky (90). Conjunction: (of a planet with the Sun) An event in which a planet and the Sun line up in our sky (90). Greatest Elongation for planets: For Mercury or Venus, the point at which it appears farthest from the Sun in our sky (90).

5. Describe the origins of the Julian and Gregorian calendars. Which one do we use today?

The Julian calendar was developed at Julius Caesar's orders to correct problems with the older Roman calendar. It added an extra day every 4 years to keep the calendar more closely synchronized with the seasons. However, over many years this was still not quite accurate enough, and the Julian calendar drifted relative to the seasons. Pope Gregory XIII ordered the calendar to be fixed. His Gregorian calendar modified the leap-year pattern so that while it still normally occurs every 4 years, we do not have leap year in century years, except for years that are divisible by 400. Today we use the Gregorian calendar.

21. The Summer solstice is east of the vernal equinox by 6 hours of right ascension.

The statement is true at all times.

17. Last night around 8:00 p.m., I saw Jupiter at an altitude of 45° in the south.

The statement makes sense, since it describes the position of Jupiter in their local sky.

11. What is special about the tropics of Cancer and Capricorn? Describe the Sun's path on the solstice at these latitudes. Do the same for the Arctic and Antarctic Circles.

The tropics of Cancer and Capricorn are the most extreme latitudes (farthest north and south) where the Sun can ever be seen directly overhead. On the solstices (summer for Cancer, winter for Capricorn), the Sun will rise north of due east (south, for winter at Capricorn), pass directly overhead, and set north of due west (south, for winter at Capricorn). The Arctic and Antarctic Circles are the northernmost and southernmost points where the Sun will be seen at least briefly on every day of the year. Alternatively, these are the southernmost and northernmost latitudes where the Sun will appear above the horizon for an entire 24-hour day at least once a year. So on the summer solstice at the Arctic Circle, the Sun will be due north at midnight, just at the horizon. It will work its way east, growing higher in the sky, until it comes around to the meridian to the south, when it will be at 47° above the horizon. It will then continue off to the west, then north, sinking back toward the horizon. On the winter solstice, the Sun will just barely appear above the horizon due south at noon. For the Antarctic circle, this situation is exactly reversed.

13. Last night I saw Venus shining brightly on the meridian at midnight.

This statement seams false. I would require that Venus be at opposition to the Sun in the sky—and, because Venus is closer to the Sun than is Earth, it is never at opposition.

1. Briefly explain the differences between (a) a sidereal day and a solar day, (b) a sidereal month and a synodic month, (c) a sidereal year and a tropical year, (d) a planet's sidereal period and its synodic period.

a. Sidereal day is a shorter day than a solar day. A solar day, is 4 minutes longer than a sidereal, and it is what we apparently see where the sun sets and rises. b. Sidereal month: sidereal month The time required for the Moon to orbit Earth once (as measured against the stars);about days. synodic month (or lunar month) The time required for a complete cycle of lunar phases, which averages about days. c. Sidereal Year:The time required for Earth to complete exactly one orbit as measured against the stars; about 20 minutes longer than the tropical year on which our calendar is based. Tropic year: The time from one spring equinox to the next, on which our calendar is based. d. A planet's sidereal period: of a planet) A planet's actual orbital period around the Sun (90). Synodic Period:(of a planet) The time between successive alignments of a planet and the Sun in our sky; measured from opposition to opposition for a planet beyond Earth's orbit, or from superior conjunction to superior conjunction for Mercury and Venus.