Earth transit of the moon

[jackdemcak]

Did anyone catch Saturday's eclipse of the moon by the earth as seen on the Earth channel 212? How many terrestrial dwellers other than astronauts have ever seen this?

 

[Ilya]

I caught that a month or so ago. Very cool!

 

[--sexy-warlock--]

Interesting. How often does this happen?

 

[Ilya]

Interesting. How often does this happen?

That's not easy to calculate, but seems to be happening rather often.

 

[Pepper]

Based on my rudimentary understanding of orbital physics, I'm guessing about once every 28 days or so.

 

[Jim S.]

The moon crosses the equator twice each month. What percentage of those crossings occur on the opposite side of the earth from the satellite? I'm much too tired to work that out.

 

[Foxbat]

FYI: There is a solar eclipse this month (not visible in the US ) but the moon's shadow should be visible on the Dish Earth channel 212. I have set up a timer to try and capture it. Here's the link to my post over in the Dish Earth thread: http://www.satelliteguys.us/dish-ne...-launch-dish-earth-channel-6.html#post1817088

 

[bluestring]

Someone must've dvr it.

 

[Ilya]

The moon crosses the equator twice each month. What percentage of those crossings occur on the opposite side of the earth from the satellite?

I think all of them!
The speed of the earth rotation is much faster, so if the view angle is wide enough, the moon should be visible at least once on those days when the moon orbit crosses the equator. Depending on the view angle and the moon orbit inclination, it is even possible that it will be visible for more than one day in a row!

 

[Ilya]

What the heck, let's calculate it!

Per Wikipedia: the geostationary orbit radius is: 26,199 mi; Earth's radius is: 3,963 mi
The angular diameter of the Earth from the satellite should be: 2 x arcsin(1/2 x 3,963 / 26,199) = 8.675 degrees,
or if we measure from the center to the edge: 4.337 degrees

Moon's orbit inclination is about 5.1 degrees - which means, if I am correct in my calculations, it should stay within 4.337 degrees of the equator, most of the time!
So, it should be passing behind the Earth within our view most of the days! About once every day for a few days in a row around the day when the Moon crosses the equator, which happens every 2 weeks or so.

However, we also need to take into account the location of the Sun: on some days the Moon may not be visible, simply because of the bright sunlight shooting straight into the lens.

 

[navychop]

Sounds good to me.

 

[Ilya]

And how long does it take for the Moon to pass behind the Earth?
Based on the above angle calculations, it should take about half an hour or less, depending on the orbital position.