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Fraser
2007-Aug-13, 03:00 PM
We're still digging through the thousands of comments and suggestions from the listener survey but we hear your requests and suggestions, and now you get to start reaping the benefits. Today we start our survey of the solar system with Mercury. What mysteries is it hiding from us? How similar is Mercury to the other rocky planets? How much do we really know about this first rock from the Sun?

<strong><a href="http://media.libsyn.com/media/astronomycast/AstroCast-070813.mp3">Episode 49: Mercury (15.3MB)</a></strong><br />&nbsp;<br />

Read the full blog entry (http://www.astronomycast.com/solar-system/episode-49-mercury/)

EricNau
2007-Aug-16, 10:29 PM
I really like this "tour of the solar system."

This is slightly off-topic, but I was surprised that there was never a mention of the Perseids on Astronomy Cast. ...A special reminder episode (remember Comet McNaught?) would have been very nice. :)

nauthiz
2007-Aug-16, 10:42 PM
I really like this "tour of the solar system."

Seconded!

I'm also liking the updates on what you and Pamela have been posting on your blogs.

Fraser
2007-Aug-18, 02:47 AM
We just recorded Venus yesterday. Should we do the Earth or just skip to Mars?

EvilEye
2007-Aug-18, 06:48 PM
Please do Earth.

And how the moon ...or the lack of it would affect the way life evolved here.

Could it have without the satellite causing our seasons, and keeping us in a stable orbit?

also...

Without the moon... would we have had a denser atmosphere?

Gwendal
2007-Aug-21, 11:13 AM
Just a small correction:

It was realized that for every two times that Mercury goes around the Sun, it rotates three times around its axis.
So one year on Mercury is one and a half days long.

Actually, one year on Mercury is half a day long.

Number of days/year=number of rotation around its axis/year -1

The Earth rotates 366 times around its axis in 1 year : each day it rotates a little more than 360 to compensate for the advance on its orbits and it adds up to a full rotation in one year.

Likewise, the moon rotates once around its axis in its course around the earth, yet a "day" lasts forever.

So if in 2 years, mercury rotates 3 times around its axis, the day lasts 2 years.

Apophis
2007-Aug-24, 08:56 AM
We just recorded Venus yesterday. Should we do the Earth or just skip to Mars?

Do Mars first. Then you can do Earth on the 52nd show. It'd make a fitting one year anniversary episode.

Lord Jubjub
2007-Aug-26, 03:41 AM
Naw, do Earth but do it from a perspective of a space probe and lander.

mandalayleigh
2007-Aug-28, 07:32 AM
I'm thirding that you do Earth first, in the correct order of the planets. I'm anal about things like that. If you do Mars first and then do Earth, or skip Earth completely, I'll feel unsettled, and I know you guys do these podcasts each week just for my enjoyment. Also, are you going to include Pluto, even though it's been demoted as a planet? I've really been enjoying these podcasts and I've just made a donation. Keep up the awesome work.

clint
2007-Aug-29, 06:04 PM
Sorry, I know we're in a science-(not fiction)oriented forum.
But still, Mercury always reminds me of that mining venture of Lando Calrissian's on Nkllon (http://starwars.wikia.com/wiki/Nomad_City)
:cool:

That fictional planet sounds a lot like Mercury:
very close to its star and rotating very slowly
(the slow rotation enables Lando to build a moving platform that always stays on the night side of the planet)

Two things I am wondering about in this context:
- how long does perceived daytime (or nighttime) last for an observer on Mercury?
- how fast would you have to move in order to stay on the night side?
(actually, you might have to move back and forth because of the weird effects of the 3:2 resonance, is that right?)
:think:

tonyman1989
2007-Sep-18, 04:20 AM
Today we start our survey of the solar system with Mercury. What mysteries is it hiding from us? How similar is Mercury to the other rocky planets? How much do we really know about this first rock from the Sun?


I really liked the mercury ep. I learn alot and I look forward to the jupiter planet.

MikeCassidy
2007-Nov-08, 01:32 PM
I would think that Mercury being so close to the Sun that the Sun's gravity cause the center of Mercury to be molten enough to 'heal over' the craters and cracks?

page13
2007-Dec-16, 05:29 AM
I can't wrap my head around the physics of gravity assist. Why does travel in the same direction of another objects orbit speed something up while travel in the opposite direction slow it down? I keep thinking that the approach push and depart pull would cancel each other out either way and not change speed at all?

Lord Jubjub
2007-Dec-18, 01:16 AM
It has all to do with approach angle and departure angle. They are not the same.

page13
2007-Dec-26, 04:21 AM
hmmmm ... thanks jubjub - but how are the angles not the same??

Another thing, Pamela was explaining how the change in Mercury's orbit through time is also a result of the sun not being a sphere - what?? To what extent is the sun flat?

PS I've never seen this before: I typed in "dickey-goldberg correction" in my google bar and it only gave me one location on the entire internet!! and it was this episode 49!! Soooo - can anyone enlighten me on what that is as well?

01101001
2007-Dec-26, 07:15 PM
but how are the angles not the same?

See diagrams at Wikipedia: Gravity assist (http://en.wikipedia.org/wiki/Gravity_assist)

01101001
2007-Dec-26, 07:28 PM
"dickey-goldberg correction"

Probably the likes of:
R. H. Dicke and H. M. Goldberg, "Solar oblateness and general relativity"

(Google Scholar search for dicke goldberg (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=dicke+goldberg))

Texas.Stargazer
2008-Oct-19, 06:35 PM
Just a small correction:


Actually, one year on Mercury is half a day long.
Number of days/year=number of rotation around its axis/year -1
The Earth rotates 366 times around its axis in 1 year : each day it rotates a little more than 360 to compensate for the advance on its orbits and it adds up to a full rotation in one year.
Likewise, the moon rotates once around its axis in its course around the earth, yet a "day" lasts forever.
So if in 2 years, mercury rotates 3 times around its axis, the day lasts 2 years.


What?? The day on the moon lasts forever??

The lunar day is 27.3 earth days long (the time it takes for lunar phases to repeat).

According to data from the Mercury Messenger mission, one day on Mercury is 176 earth days and one year on Mercury is 88 earth days. So one year on Mercury is indeed, like Pamela said, one and a half Mercury days long.

Here's a great animation that shows visually why this is true.

http://btc.montana.edu/messenger/Interactives/ANIMATIONS/Day_On_Mercury/day_on_mercury_full.htm

clint
2008-Oct-20, 09:26 AM
Here's a great animation that shows visually why this is true.
http://btc.montana.edu/messenger/Interactives/ANIMATIONS/Day_On_Mercury/day_on_mercury_full.htm

Nice!

The sun looks a bit small though, doesn't it?
Seen from Mercury, I would expect it to be huge...

timb
2008-Oct-20, 11:16 AM
What?? The day on the moon lasts forever??

The lunar day is 27.3 earth days long (the time it takes for lunar phases to repeat).

According to data from the Mercury Messenger mission, one day on Mercury is 176 earth days and one year on Mercury is 88 earth days. So one year on Mercury is indeed, like Pamela said, one and a half Mercury days long.



Two times 88 was 176 last time I checked. I guess they had adopted the "New Math" by the time you went to school.

Empyre
2008-Oct-21, 01:09 AM
So basically, Mercury's solar day and sidereal day are vastly different.

timb
2008-Oct-21, 02:58 AM
So basically, Mercury's solar day and sidereal day are vastly different.

That's how is when the sidereal day and the year aren't that different.