Wednesday, February 29, 2012

Intercalary years (aka bissextile or leap years)

Shifting of the date of the summer solstice
from Absolute Astronomy

Every four years we add a day to our calendar: 29 February. We call this a "leap year," or an "intercalary year," or a "bissextile year." A year that is not a leap year is called a "common year."

Why?

This is necessary in order to keep our calendar (Gregorian) in sync with the seasonal year because the day is not exactly 24 hours long and extra time accumulates every year at the rate of about 1/4 of a day. In other words, our year is not 365 days, it's 365.25 days long. In order to keep things accurate, we add an entire day every fourth year.

Side note: On a much smaller scale, we also add leap seconds occasionally because the solar day becomes 1.7 milliseconds longer each century due to tidal friction. This information is tracked with atomic clocks by the  International Earth Rotation and Reference Systems Service (IERS). It will be a very, very long time before we have a 366-day year (billions of years).


More information...
Leap year/day
"Leap year: 2012 is a Leap Year" (timeanddate.com)
"Why we have leap days" (Bad Astronomy/Discover)
"LeapYear" (Wolfram Research)
"Leap years and leap seconds" (Royal Museums Greenwich, UK)
"Leap Years" (United States Naval Observatory (USNO))
General information & traditions (Wikipedia)
Galileo Day Campaign (Somnabulist)


Gregorian calendar
Absolute Astronomy
Wolfram Research
The Galileo Project

Tuesday, February 28, 2012

Daylight Saving Time: 2012


 from WikiMedia Commons
So, when exactly do we reset our clocks? And is it forward or backward one hour?

Daylight Saving Time can be very confusing. Read below to help end your confusion! [The chart on the left plots the times of sunrise and sunset (with DST adjustment as separate lines) in Greenwich, GB for 2007.]

Short answer
For the Spring- On Sunday, 11 March, 2012 at 2:00am, you should set your clock forward one hour to 3:00am.

For the Fall- On Sunday, 04 November, 2012 at 2:00am, you should set your clock backward one hour to 1:00am. (Remember "spring forward, fall back...").

Easy answer: Most people who go to bed earlier than the wee hours of the morning simply set their clocks back/forward one hour before they go to bed on Saturday.

Detailed answer: Go HERE.

For more information...
Daylight Saving Time from WebExhibits

World Clock for Indianapolis DST

National Geographic on DST

US Naval Observatory on DST

Figure out what time it is in the United States at Time.gov