time and calendar

Link calendars, consecutive days, universal time and sidereal clocks to prepare time coordinates for event calculations.

Starting from the Julian day; sidereal time and mean time difference can be studied in combination with observation topics.

Let’s look at the phenomena in life first →

• When the calendar changes a page, how do astronomers change their time numbers?

  Drag the clock through the day and see how the calendar and consecutive day numbers describe the same moment.

• For an ancient observation date, would it be wrong to change it to consecutive days?

  The same year, month and day may not be the same day if the calendar is different; choose the rule first and then check both ways.

• Is the 60th day of this year February 29th or March 1st?

  Dates, days of the week, and year numbers are all different labels for the same day.

• Why does Easter change its date every year, sometimes not on the same day?

  Turn the same year into two calendars and see how the rules select Sunday.

• Months are also recorded according to the moon. Why do some calendars have an extra month?

  Arrange the months of the whole year into strips and see what problems each leap month and leap day solve.

• I only pressed the shutter once, why are there two times in the record?

  The same moment can be marked by two sets of timing scales, and different readings do not mean that it happened twice.

• Do people in the past and people today have the same difference in earth clocks?

  If you want to check the chronology of ΔT, you cannot apply one number from today or an old book to all history.

• The same window, the same hour, why do the stars move every few days?

  Take photos at the same location and at the same time every day, and let the window frame remember the position of the stars for you.

• Why do we need to distinguish between "mean" and "apparent" sidereal time when the telescope is pointed at the same star?

  The Earth's rotation gives the general direction, and small changes in the reference zero point of the celestial sphere will also bring about second-level corrections.

• The sundial said twelve o'clock, why hasn't the clock arrived yet?

  The sun is not a uniform clock. First compare the two sets of solar times at the same instant.