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James: Welcome to "Star Gazers". I'm James Albury, Director of the Kika Silva Pla Planetarium in Gainesville, Florida.
Dean: And I'm Dean Regas, Outreach Astronomer from the Cincinnati Observatory. We're both here to help you be sure you know what you're seeing in the night sky when you...
Both: Look up.
James: Every four years, we get to experience something unique that became a part of our culture specifically because of the Earth's orbit around the Sun.
Dean: That's right, James. And although this event seems to happen every four years, sometimes we skip a year.
James: Indeed, and we also have some interesting planet/moon pairings to show you too. Wondering what were talking about? Let's show you!
Dean: O.K., we've got our skies set up for
any night next week.
and if you look at the night sky, you'll notice that the constellations
that you saw last year at this time are in exactly the same place.
James: Yep! And did you know that if you went outside at midnight on your birthday every year, you'd see exactly the same star patterns? The planets and Moon would all be in different positions each year, but the stars appear to be in the same place.
Dean: Indeed, and every four years, we have to add one whole day to our calendar to make sure that the star patterns you see on your birthday are exactly the same, year after year.
James: This is because the time it takes for the Earth to travel around the Sun doesn't exactly match our calendar year. As you know it takes approximately 24 hours for the Earth to rotate once on its axis. That's one day. And it takes almost 28 days for the Moon to orbit the Earth. That's one month.
Dean: But a year is how long it takes for a planet to travel all the way around the Sun and return to the same spot. It takes Earth approximately 365 days, 6 hours to travel around the Sun once. Over time, this extra six hours started causing problems for our calendar, because after a few decades, timekeepers noticed that we were almost a week behind in our journey around the Sun than where we should have been according to our calendar. So what did they do? They added extra time to the calendar to compensate.
James: And since we're off by 6 hours a year, every 4 years we'd be almost an entire day behind where we should be (according to our calendar). Since 6 hours each year for 4 years adds up to 24 hours, it was decided that the simplest way to fix things was to add an extra day to the calendar every 4 years.
Dean: Years when we do this are called Leap Years and the day which we add to our calendar count is called a Leap Day. Now where should we put it? Well February has the least number of days. So let's add it to February and we'll come up with February 29th. We traditionally experience a Leap Year in years that are evenly divisible by 4; like 2008, 2012 and 2016.
James: However, when a century ends, we skip a leap year. The exception is if the century ends on a year that is exactly divisible by 4. So, as I'm sure you remember, 1800 and 1900 weren't Leap Years, but 1600 and 2000 were Leap Years. Going forward in time, you'll notice that 2100, 2200 and 2300 won't have a Leap Day but 2400 will.
Dean: The reason the 'end of century' rule was introduced is because the correction is too big. The 6 hours is actually rounded up from 5 hours, 49 minutes and 16 seconds. But eh who's counting?
James: O.K, let's go see what the planets and our Moon are doing this leap day week.
Dean: If you go outside just after sunset any night this week, you'll be able to see our Moon, accompanied by four planets, all in the sky at the same time. Low on the horizon is the closest planet to the Sun, Mercury, and just above it, is the brightest planet visible from Earth, our sister planet, Venus. If you look at Venus through a telescope you'll notice that it's in a waning gibbous phase, on its way around to our side of the solar system for its transit of the Sun in early June 2012.
James: And, just above Venus is the largest planet in our solar system Jupiter. And in just a few weeks, Jupiter and Venus will appear less than 3 degrees away from each other on March 12th. And lastly is our friend the red planet, Mars. Mars is at opposition this week, so it'll be at its biggest and brightest over the next few days, so get outside and check it out!
Dean: O.K., my friends! Enjoy your extra day this year
James: And remember, whatever you do
Both: Keep looking up!
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James: Every four years, we get to experience
Leap Day because of the Earth's orbit around the Sun.
Dean: And because of this, if you go outside on your birthday every year, you'll notice the star patterns you can see are exactly the same.
James: Let's show you!
Dean: O.K., we've got our skies set up for the last week of February, and on February 29th, we'll be experiencing a Leap Day.
James: Yep! And that's because the time it takes for us to orbit the Sun is approximately 365 days, 6 hours, so every four years we have to add one whole day to our calendar to make up for those extra hours. As a result, the star patterns you can see on your birthday are exactly the same, year after year!
Dean: This year if you go outside on leap day, you'll see our Moon and four planets in the sky right after sunset. Pinkish mercury, close to the horizon
James: Brilliant Venus and Jupiter just above Mercury
Dean: And rising in the east, the red planet Mars, which will be at its biggest and brightest this week!
Both: Keep looking up!
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Please give us your comments. (Click
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* This week's Sky At A Glance and
Planet Roundup from Sky & Telescope.
Starry Night 6 was used to produce this episode
of Star Gazer
![[SmilinJack]](jack1sm.jpg)
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