Tag Archives: orbit

Making Friends with the Night Sky: The New Moon

A glimpse of the moon through the trees, as it phases from new moon to cresent.

A glimpse of the moon through the trees, as it phases from new moon to cresent.

Maui astronomer Harriet Witt describes the new moon, the start of the lunar cycle.

Listen here [3:26m]:

Download here [8.1 Mb]: ftp://space.mit.edu/pub/ajb/radiopio/astrofacts_090722_mfns-moonnew.mp3

What’s the facts:

“A month is a Moonth, a Moonth is a moon.”  For many traditional calendars – Hawaiian, Chinese, Hebrew, Islamic – this is still true, although our western calendar has been tweaked to fit the months into one year.  The new moon is the start of the lunar month, and the time when the moon lies between the Sun and the Earth (this is called syzygy, a great Scrabble word).  Imagine yourself floating out in space well above the Sun, Moon and Earth, and you will see these three bodies in a row, with the Sun-lit side of the Moon facing away from the Earth.  So where is the new Moon in the sky?  Directly in front the Sun!

Why doesn’t the Moon block, or eclipse, the Sun every time the new moon phase happens?  It’s because the plane of the Moon’s orbit is actually inclined by about 5° relative to the plane of the Earth’s orbit (the ecliptic plane).  So most of the time, the Sun, Moon and Earth are out of alignment during new moon.  However, the Moon’s orbit actually rotates, or precesses, every 27.2 days.  So perfect alignment at new moon occurs about once every 18 years, a period the Babylonians called a Saros cycle (a complete explanation can be found here).  In fact, there are several Saros eclipse cycles because the Sun-Moon-Earth alignment doesn’t have to be perfect, so we get about two eclipses at new moon every year.

New moon is a great time for star-gazing as the Sun and the Moon will have both set in the evening.  So be sure to enjoy the dark skies that accompany the new Moon!

Original air date 22 July 2009.

So you think you can orbit?

Pluto & Charon do the perpendicular binary hip-hop

Pluto & Charon do the perpendicular binary hip-hop

Pluto and Charon dance it off in the intergalactic smash hit “So you think you can orbit?”  Can their perpendicular orbit help them win it all?

Listen here [2:02m]:

Download here [1.9 Mb]: ftp://space.mit.edu/pub/ajb/radiopio/astrofacts_090813_soyouthinkyoucanorbit.mp3

What’s the facts:

Pluto, the second-largest known dwarf planet in the Solar System (after Eris), and its largest moon, Charon, are sometimes treated as a binary system, because the center of their orbit does not lie within either body (Charon is about half as big and 1/7th as massive as Pluto).   Indeed, before its re-classification, Pluto and Charon were the closest thing to a double planet known.  The orbit of Pluto and Charon is also special in that it is nearly perpendicular to the plane of their mutual orbit around the Sun, like a record rolling on its side (Uranus and its moons are tilted over in a similar way).  As such, the Pluto-Charon orbit can be seen either face-on – like a clock – or edge-on – like a thrown frisbee – during its 248-year trek around the Sun. Between 1985 and 1990 the orbit was aligned edge-on so that the two bodies repeatedly passed in front of each other, or eclipsed.  These eclipses allowed astronomers to measure both the sizes of Pluto and Charon as well as make a rough map of Pluto’s surface features.  Finally, Pluto and Charon are the only planet-moon pair whose orbit and rotations are mutual synchronized; that is, they both face the same face to each other all the time. This makes Pluto and Charon excellent partners as the dance their way through space!

Original air date 13 August 2009.

Making Friends with the Night Sky: What is Night?

The Earth...at night!

The Earth...at night!

Maui astronomer Harriet Witt asks a simple question: what is night?  The answer requires us to view our planet from a completely different perspective. The answer just might surprise you.

Listen here [4:24m]:

What’s the facts:

Night or nighttime is the period of time when the sun is below the horizon. Nights are shorter than days on average, but vary in length as it is based on factors such as season, latitude, longitude and timezone. Night lets our bodies know when to sleep and when animals can go out to hunt, but it’s also important to science. Without the absence of the Sun, we may never have seen the stars in the sky, and astronomy would not be what it is today. So next time you’re taking out the trash and you get spooked when something stirs in the dark, take a minute to look at the sky and appreciate it, and remember that light is right around the corner.

Original air date 30 June 2009.

Uranus – what’s with the name?

Uranus stinks!

Uranus stinks!

Yer Anus?!? Did she just say what I think she said? Oh I see. Uranus! Well, you should have just said so in the first place! Makena and Charae’ ask Professor B about some of the characteristics of Uranus as they look at it through their binoculars. You can learn a lot from just looking at the sky from your backyard.

Listen here [3:36m]:

What’s the facts:

Uranus was discovered by William Herschel, in 1781. This planet is strange to the solar system in many ways. Though most planets rotate on an axis perpendicular to it’s elliptical orbit around the Sun, Uranus’ axis is nearly parallel to it, so it’s rolling like a barrel on its side. Uranus is composed primarily of rock and various ices, and its atmosphere is about 83% hydrogen, 15% helium and 2% methane. The methane (a chemical that’s also in cigarettes, yuck!) in Uranus’ upper atmosphere absorbs red light and reflects blue light, giving the planet a blue appearance. Uranus has 27 fascinating moons, named mostly afters Shakespeare characters and a complicated ring systemOne year on Uranus is the equivalent to about 84 years on Earth, but it’s day (rotation around it’s axis) is only a little more than 17 Earth-hours. Careful pronunciation may be necessary to avoid embarrassment; say “YOOR a nus” , not “your anus” or “urine us”.

Original air date 4 April 2009.