- circumpolar stars: stars that do not rise or set and are visible all night on a clear night. The closer you are to the north pole, more stars will be circumpolar.
- Copernicus: developed heliocentric model
- ecliptic: apparent path of sun across the sky
- equinox: when sun is overhead at equator, and the length of daylight is the same at all latitudes (twice a year, about March 21 and September 21)
- Galileo: first to use a telescope for astronomy
- Gregorian calendar: calendar with 365 days in ordinary years and 366 days in leap years. A year is a leap year if it is divisible by 4, unless it is divisible by 100 in which case it is not a leap year unless it is also divisible by 400. Therefore, 1700, 1800, and 1900 were not leap years; 2000 was a leap year.
- Julian calendar: calendar where every fourth year is a leap year
- Kepler: derived three laws of planetary motion
- latitude: north/south coordinate on Earth
- longitude: east/west coordinate on Earth
- lunar eclipse: the Earth is between the sun and the moon, so the Earth's shadow is visible on the moon
- meridian: circle on the sky beginning on the horizon due north, passing through the zenith, and ending at the horizon due south
- Newtonian reflector telescope:
- opposition: when a planet is opposite the sun in the sky, so it rises at sunset and sets at sunrise
- Ptolemy: developed geocentric model (in ancient world)
- reflector and refractor telescopes: reflector: mirror; refractor: lens
- seasons on Earth: caused by tilt of Earth's axis
- sidereal day:
- Note: a sidereal day is 23 hours, 56 minutes long. This means that a star will rise 4 minutes earlier tomorrow than it will tonight. If you wait one week, a star will rise about one-half hour earlier. If you wait one month, a star will rise about two hours earlier. If you wait twelve months, a star will rise 24 hours earlier -- that is, it will be back to rising at the same time that it rises tonight.
- sidereal time: a measure of how much the celestial sphere has turned
- solstice: summer solstice about June 21: the sun is overhead at noon at the Tropic
of Cancer (about the latitude of Hawaii); longest day of the year in the northern
hemisphere
winter solstice: about December 21: the sun is overhead at noon at the Tropic of Capricorn in the southern hemisphere; shortest day of the year in the northern hemisphere - Tycho: made precise observations of planetary positions; Kepler used his data
- zenith: the point in the sky directly overhead
- zodiac: the group of 12 constellations through which the ecliptic passes, so the sun, moon, and planets are always seen in one of these constellations (optoinal technical note: there is actually a 13th constellation, Ophiuchus, through which the ecliptic passes)
You cannot determine longitude just from observations of the sky. (To determine longitude you would also need a clock.)
latitude=elevation of Polaris (making the approximation that Polaris is at declination 90)
The year under the Julian calendar was too long, so the calendar was no longer matching the seasons.
What stars will be circumpolar from each of these cities (give their declinations)?
What will be the elevation of Polaris from each of these cities? (Assume that Polaris is at declination 90 degrees -- which is a good approximation for its true value of about 89 degrees).
| City | Latitude | Farthest south declination | circumpolar stars will be north of | elevation of Polaris | |
| Jerusalem | 32 | -58 | 58 | 32 | |
| Paris | 49 | -41 | 41 | 49 | |
| Quito | 0 | -90 | 90 | 0 | |
| Anchorage | 61 | -29 | 29 | 61 |
Because these cities all have the same latitude, the sky will be the same. (The only difference would be events such as eclipses that depend very precisely on the time.)
200/2.5 = 80