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Objectives. Understand what the Modified Julian Calendar is and why it was made. Be able to tell today’s date in the Modified Julian Calendar. Understand Universal Transverse Mercator. Be familiar with Celestial and Galactic Coordinate Systems.

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## Objectives

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**Objectives**• Understand what the Modified Julian Calendar is and why it was made. • Be able to tell today’s date in the Modified Julian Calendar. • Understand Universal Transverse Mercator. • Be familiar with Celestial and Galactic Coordinate Systems. • Be able to find and place objects on a Galactic Coordinate map • Understand why these are used in Cosmic Ray detection.**Modified Julian Calendar**• In 1583 a French scholar, Joseph Justus Scaliger, invented the Julian Period. • It was designed to replace Western calendars which were based on the ruling eras of nation.**Modified Julian Calendar**• The Julian period is equal to 7980 years of exactly 365.25 days • 7980 is based off of the time it takes for three common cycles of the time to align again at (1,1,1) • 28 year solar cycle • 19 year lunar cycle • 15 year Roman indiction cycle 28 (Solar) * 19 (Lunar) * 15 (Indiction) = 7980**Modified Julian Calendar**• The solar cycle is the time that it takes for calendar days of years to repeat. • Thus you only ever need to own 28 consecutive calendars.**Modified Julian Calendar**• The lunar cycle is the time it takes for the moon to be approximately the same phase at the beginning of the year • In other words there are 19 years in between years that begin with a full moon**Modified Julian Calendar**• The indiction cycle is an old Roman tax period • It has historical importance because dates were often recorded using this cycle • No one knows where it came from**Modified Julian Calendar**• Scaliger determined what year the solar and indiction cycles were in in the year of Christ’s birth • The solar cycle was in the 9th year • The indiction cycle was in the 3rd year • The lunar cycle was set to 1 on that year and so year 1 in our calendar became (9,1,3) or the 4713rd year • The year 4713 B.C. then became the first year in the Julian Period**Modified Julian Calendar**• The calendar started at 0 at noon on January 1st 4713 B.C. • Each day adds 1 to the count with partial days adding a partial count • i.e. 12 hours adds .5 to the count • 3 hours adds .125 • 18 hours and 30 min. adds .77083 • Today’s date is very long • 2451809.5 is midnight Sept. 22, 2000 • Recently the Modified Julian Calendar has been put into use**Modified Julian Calendar**• The modified Julian calendar has 2 primary benefits • The Julian day number is reduced in length by at least 2 digits • The day begins at midnight instead of noon • The modified Julian calendar day equals the Julian calendar day minus 2400000.5 • Zero is now midnight Nov. 17, 1858 • All dates there after are consecutive just like the Julian Calendar**Why Do We Care?This Won’t Ever Come Up! (Will It?)**• On June 15, 763 B.C. there was a solar eclipse seen at Nineveh. • On April 14 425 B.C. there was a lunar eclipse seen at Nineveh. • How many days elapsed between these two celestial events?**Same Example Using Julian Days**• On the Julian Date of 1,442,903 there was a solar eclipse seen at Nineveh. • On the Julian Date of 1,566,296 there was a solar eclipse seen at Nineveh. • Now it is easy to see that there were 123,393 days between these two recorded celestial events.**The Galaxy Awaits**• The Earth is a wonderful place and all, but how can we locate things that aren’t on Earth. • One of the major issues currently with Cosmic Rays is determining where they come from. • Once we determine where they come from, how do we keep track of that location? A very perplexing problem!**Don’t Worry Homer**• Luckily for us, Astronomers have devised ways to locate and map objects. • It is called Galactic Coordinates. And it looks like this:**Our Galaxy(Aren’t We Pretty?)**Galaxy Center

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