GEN 09: Time 2

📄 Detailed Notes⚡ Cheat Sheet
 

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📄 Notes ⚡ Cheat Sheet
📄 Notes ⚡ Cheat Sheet

Q1. Civil twilight is defined by :

sun altitude is 6° below the celestial horizon –

  • Civil Twilight ends when the geometric center of the sun is 6 degrees below the sensible horizon. (12° is Nautical, 18° is Astronomical).

    • Q2. At what times of the year does the length of the hours of daylight change most rapidly?

    Spring Equinox and Autumn Equinox –

  • The rate of change of the Sun’s declination is greatest when it crosses the Equator (the Equinoxes), resulting in the most rapid change in daylight duration.

    • Q3. Seasons are due to the:

    inclination of the polar axis with the ecliptic plane –

  • The tilt of the Earth’s axis (obliquity of the ecliptic, approx 23.5°) relative to its orbital plane causes the variation in solar angle and day length that creates seasons.

    • Q4. At what approximate date is the earth furthest from the sun (aphelion)?

    Beginning of July –

  • Aphelion occurs typically around July 4th. Perihelion occurs around January 3rd/4th.

    • Q5. Assuming mid-latitudes (40° to 50°N/S). At which time of year is the relationship between the length of day and night, as well as the rate of change of declination of the sun, changing at the greatest rate?

    Spring equinox and autumn equinox –

  • Consistent with the previous question, the rate of change is maximum at the equinoxes.

    • Q6. What is the highest latitude listed below at which the sun will reach an altitude of 90° above the horizon at some time during the year?

    23° –

  • The Sun is only directly overhead (90° altitude) between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S). 23° is the only option within this range.

    • Q7. The declination of a celestial body (the Sun) measured on the Celestial Sphere is analogous (equivalent) to _________ on the Earth?

    latitude –

  • Declination is the angular distance north or south of the Celestial Equator, corresponding to Latitude on Earth. (GHA/SHA corresponds to Longitude).

    • Q8. The duration of civil twilight is the time:

    between sunset and when the centre of the sun is 6° below the true horizon –

  • Standard definition of Civil Twilight duration.

    • Q9. The angle between the plane of the ecliptic and the plane of equator is approximately:

    23.5° –

  • This is the Obliquity of the Ecliptic (Earth’s axial tilt).

    • Q10. The main reason that day and night, throughout the year, have different duration, is due to the:

    inclination of the ecliptic to the equator –

  • The tilt causes the circle of illumination to divide parallels of latitude unequally (except at the Equator), creating variable day/night lengths.

    • Q11. What is the duration of civil twilight?

    From the moment when the tip of the Sun disappears below the visual horizon until the centre reaches a depression angle of 6° from the sensible horizon. –

  • Technically, twilight begins at Sunset (Upper limb/Tip disappears). It ends when the geometric center is 6° below.

    • Q12. Which is the lowest latitude listed below at which the sun will rise above the horizon and set every day?

    66° –

  • Note: This question wording is tricky. 68° and 72° experience 24-hour daylight/darkness. 62° and 66° both have daily sunrises/sunsets. However, 66.5° (Arctic Circle) is the limiting latitude for this behavior. In aviation exams, 66° is typically the correct answer as it represents the boundary condition (closest to the Polar Circle).

    • Q13. At what approximate date is the earth closest to the sun (perihelion)?

    Beginning of January –

  • Perihelion occurs approx Jan 3-4.

    • Q14. Viewed from the North Celestial Pole (above the North Pole), the Earth orbits the Sun:

    anticlockwise in an elliptical orbit –

  • All solar system planets revolve anticlockwise (Prograde) when viewed from the North, in elliptical orbits (Kepler’s 1st Law).

    • Q15. In which two months of the year is the difference between the transit of the Apparent Sun and Mean Sun across the Greenwich Meridian the greatest?

    February and November –

  • This refers to the “Equation of Time” (Apparent Solar Time – Mean Solar Time). The difference peaks at approx -14 mins in February and +16 mins in November.

    • Q16. When do the ‘equinoxes’ occur?

    March and September –

  • Vernal Equinox (~March 21) and Autumnal Equinox (~Sept 23).

    • Q17. In the Air Almanac the symbol //// stands for?

    Q18. The main reason that day and night, throughout the year, have different duration, is due to the?

    Q19. In which months is the difference between apparent noon and mean noon the greatest?

    Q20. What is the reason for seasonal changes in climate?

    Q21. The angle between the plane of the ecliptic and the plane of equator is approximately?

    Q22. At what approximate date is the earth furthestSrom the sun (aphelion)?

    Q23. At what times of the year does the length of the hours of daylight change most rapidly?

    Q24. Civil Twilight occurs between?

    Q25. What is the highest latitude on the Earth at which the sun can be vertically overhead?

    Q26. The UTC of the end of evening civil twilight in position 51°N 008ºW on 15 August is?

    Q27. The duration of civil twilight is the.time?

    Q28. Which is the highest latitude listed below at which the sun will rise above the horizon and set every day?

    Q29. In which two months of the year is the difference between the transit of the Apparent Sun and Mean Sun across the Greenwich Meridian the greatest?

    Q30. What is the highest latitude listed below at which the sun will reach an angle of 90° above the horizon at some time during the year?

    Q31. Assuming mid-latitudes (40° to 50°N/S). At which time of year is the relationship between the length of day and night, as well as the rate of change of declination of the sun, changing at the greatest rate?

    Q32. At which of the following latitudes does the maximum difference between geodetic and geocentric latitude occur?

    Q33. When standing at the South Pole in which direction will you be facing?

    Q34. The angle between the plane of the ecliptic and the plane of equator is ‹approximately :

    Q35. Which is the highest latitude listed below at which the sun will rise above the horizon and set every day?

    Q36. In which two months of the year is the difference between the transit of the In which two months of the year is the difference between the transit of the

    Q37. Assuming mid-latitudes (40° to 50°N/S).At which time of year is the relationship between the length of day and night, as well as the rate of change of declination of the sun, changing at the greatest rate?

    Q38. The length of apparent solar day varies due to

    Q39. Mean solar day is the time interval between:

    Q40. The morning civil twilights begins and evening civil twilights ends when

    Q41. Mark the correct statement

    An apparent solar day is always longer than a sidereal day. While the length of the solar day varies slightly throughout the year (ranging from slightly shorter or longer than the average 24 hours due to Earth’s elliptical orbit and axial tilt), it never becomes shorter than the sidereal day.

    Sidereal Day: This is the time it takes for Earth to complete one full 360° rotation relative to distant stars, lasting approximately 23 hours, 56 minutes, and 4 seconds.

    Solar Day: Because Earth moves along its orbit around the Sun while rotating, it must rotate an additional ~1 degree (taking about 4 minutes) to bring the Sun back to the same position in the sky.

    Variation: The apparent solar day varies in length because Earth’s orbital speed changes (faster at perihelion, slower at aphelion) and the Sun’s path is not parallel to the celestial equator, causing the solar day to sometimes be longer or shorter than the mean solar day of exactly 24 hours, but it remains longer than the fixed sidereal day.

    Sidereal time - Wikipedia

    Q42. When does perihelion occur?

    Q43. When does aphelion occur?

    Q44. When do the ‘equinoxes’ occur?

    Q45. When it is the Winter Solstice in the Southern hemisphere, the Declination of the Sun is:

    Q46. What is the angle between the planes of the Equinoctial and the Ecliptic?

    Q47. The declination of a celestial body (the Sun) measured on the Celestial Sphere is analogous (equivalent) to ________________ on the Earth?

    Q48. ‘The length of daylight/night depends upon the declination of the Sun and the latitude of the observer’. When is the rate of change of the length of daylight greatest?

    Q49. A sidereal day is:

    Q50. The maximum difference between mean noon (1200LMT) and real/apparent noon occurs in ________?

    Q51. The maximum difference between mean time and apparent time is:

    Q52. What is the length of a Sidereal Year?

    Q53. The Hour Angle (Greenwich Hour Angle) of a celestial body is analogous/ equivalent on the Earth to ________?

    Q54. A star has a Greenwich Hour Angle (GHA) of 220°. Which meridian is the star transiting (crossing)?

    Q55. On Mid-summer Day in the Southern hemisphere, the Sun will be overhead:

    Q56. On Mid-winter Day in the Northern hemisphere, the Sun will be overhead:

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