I happened to look out the kitchen window while doing the dinner dishes on Monday (October 15), and what did I see? The gorgeous crescent Moon underneath the bright "star" of Jupiter.
I ran out and took a bunch of images; the one above is arguably the best. I didn’t even notice Antares, the star to the right of the Moon (on the other side of the tree), when I took the shots!
As I was taking the pictures, I pondered how far below Jupiter the Moon was. Holding up my fist as a gauge, I reckoned they were about 5 degrees apart. Hey, I thought. The Moon must be at its most southernly ecliptic latitude!
I think things like this because I am a geek. But face it, you are too. You read my blog.
And so, because you’re dying to know, here’s what I was thinking:
The Earth orbits the Sun (with me so far?). Over the year, that means it looks like the Sun makes a big circle in the sky relative to the stars. We call that path the ecliptic. The major planets all orbit the Sun in roughly the same plane, so they stick to the ecliptic too. Not exactly on it, but pretty close.
The Moon, however, orbits the Earth in a plane tilted to the ecliptic by about 5 degrees (think two hula hoops, one jammed inside the other, and then tilted a little bit). That’s why we don’t get a solar eclipse every month: the two planes (ecliptic and Moon orbit) need to intersect when the Moon happens to be new, between the Earth and the Sun. Otherwise, it might miss the Sun’s position by as much as +/- 5 degrees.
So when I saw the Moon and Jupiter on Monday, I knew the Moon had to be dipped down as low below the ecliptic as it can go. I looked up the ecliptic latitude of the Moon for that night, and bango! -5 degrees. Cool.
Science! It makes things predictable.
October 16th, 2007 at 10:11 pm
I’ve got a question: “Also bear in mind that creationists were the first to seriously question Lyellian Uniformitarianism and that the evolutionary geologists didn’t abandon it until the 1970’s, due to their realization by observation that canyons can be created extremely rapidly–in a matter of days or weeks, depending on a water source.”
Is that true?
October 16th, 2007 at 10:32 pm
Back on topic…. BEAUTIFUL. Our universe is so beautiful.
October 16th, 2007 at 11:04 pm
It sounds like a creationist told you that, so the answer is “no, for most definitions of the word true.”
It is probably true that creationists were the first to question anything even remotely having to do with the idea of an old earth or evolution, especially since the people coming up with those theories were themselves creationists: pretty much everyone in Western Europe was around that time.
It might be true that “evolutionary geologists” abandoned “Lyellian Uniformitarianism”, though this is mostly dependent upon the person making the original statement having some personal definition of “Lyellian Uniformitarianism” beyond “the processes that currently shape the earth have been doing so for a long time, and are what created (most of) the geological forms we see today.”
If by creating a canyon, the creationist means burrowing through loose soil or ash, then yes, water can probably do that fairly quickly. If the creationist means the Grand Canyon, then no, that took around 6 million years to dig. Period.
October 16th, 2007 at 11:22 pm
Hey, Phil! It’s also worth pointing out that the Moon’s orbital tilt of 5 degrees being to the ecliptic makes it (I believe) unique among planetary satellites, all the rest of whose orbital inclinations are to their parent planets’ equators. In each case the satellite orbital plane then wobbles around the parent planet equator, keeping about the same tilt to that plane. (The Moon’s orbit also wobbles, but again, about the ecliptic. Exceptions to this regularity are some of the more distant Jovian and Saturnian satellites, which have chaotic orbits?)
It is as though our Moon is taking its marching orders more from the Sun than from the Earth. This, and the fact that the Moon’s path around the Sun is everywhere concave toward the Sun (also unique?), make it reasonable to call the Earth-Moon system a double planet. (These and the relatively small planet-satellite mass ratio, 81.3, which until Charon was discovered, was by far the smallest of any known planetary satellite in the solar system.)
Echoing the second comment, yes, our universe IS beautiful, including its orderliness, and the complexity of that orderliness!
October 17th, 2007 at 12:08 am
What a great Universe!
October 17th, 2007 at 1:16 am
Phil,
I’m having trouble understanding the difference between the ecliptic you describe and the analemma as shown in the APOD below.
http://antwrp.gsfc.nasa.gov/apod/ap071002.html
October 17th, 2007 at 1:58 am
Steve P.: The figure-eight analemma is a combined effect of Earth’s elliptic orbit and its 23.5 degree tilt.
No, I didn’t come up with that by myself, I’m a theoretical astrophysicist in training, not a practical one, and theoreticians google things.
These two pages for example were interesting: http://members.aol.com/jwholtz/analemma/analemma.htm and http://www.uwm.edu/~kahl/Images/Weather/Other/analemma.html
October 17th, 2007 at 4:12 am
Great post (as (nearly) always). But on reading the sentence “Over the year, that means it looks like the Sun makes a big circle in the sky relative to the stars.”, I thought, I’d take the opportunity to ask a question that has puzzeled me for years. I’ve heard or read such a statement at least a hundred times, but I never really understood it. Don’t laugh, but my problem here is this: how can the sun make a big circle in sky relative to the stars, when we (or at least I) never see the sun and the stars together in the sky? (Yes, I mean this as a serious question, and no, I’m not some flat earth crackpot and I also don’t believe that NASA is messing around with the planetary orbits)
October 17th, 2007 at 4:28 am
Did you know that you can balance eggs on end when the moon is at its southernmost ecliptic?
October 17th, 2007 at 4:34 am
Did you know that you can balance eggs on end when the moon is at its southernmost ecliptic?
Har har.
I heard if you throw a dead cat into a cemetery when the moon is at its southernmost ecliptic, you really annoy the groundskeeper.
October 17th, 2007 at 4:36 am
Off-topic; astrology ad: “Calculate your love compatibility” leads to http://try.starware.com/tb/landing/horoscopes/horoscopes_wizard.php?aff_id=tribalfusionint_lv-anim-cl2-728×90 seen on top of page (long rectangle) as well as inbetween blog posts (square).
October 17th, 2007 at 5:34 am
“Bango” should be the word of the day.
October 17th, 2007 at 6:35 am
And because there are new people here, who haven’t seen it yet: Science: It works, bitches!
Michael H: You may not be able to see the stars in the sky with the sun, but they’re still there. And we know where they are (there’s that whole “making things predictable” thing again!), right? So even though they’re not visible at the time, we know where the sun is relative to the stars at any time.
Maybe this will help you think about it. Draw a picture with a dot for the sun and a circle around it representing the Earth’s orbit. Say that in January the Earth is at the left edge of the circle. Then from the Earth the sun is in the “right” half of the sky, so we can see the stars in the “left” half of the sky. Then 6 months later, the Earth is on the other half of the orbit, so we can see the stars that are toward the right side of your drawing. So if we wait a year, we can see all the stars, so we know where they are, even if we can’t see half of them at any particular moment.
October 17th, 2007 at 7:10 am
Michael H.:
In addition to Johnny Vector’s point, two others:
You can’t see the Sun and stars in full daylight, but at dawn and dusk you can see some stars and it’s not hard to infer the Sun’s position against the background sky.
Today, we have the SOHO satellite that observes the Sun continually, and it can see nearby stars — so we can directly observe the position of the Sun.
October 17th, 2007 at 7:59 am
So how it comes you can’t see stars on the Apollo photos in the sky of the moon?
BA’s photo clearly shows it must be possible.
BTW: Very nice pic!
Andre
October 17th, 2007 at 8:06 am
I’ve got a question that has been nagging me ever since we moved up north (Stavanger, Norway 58 degrees N)
Every month (as compared to every year with the sun) the moon sets at a different point on the horizon, SW to NW. This also coincides with the phase of the moon. Full moons set far to the NW, fingernail moons to the SW. (I’m still looking for the new moon…)
Why is there a correlation? Just chance? I doubt it.
Also BABlogger, how did you know that the moon had dipped a far as it could go based on its positioni vi a vis Jupiter?
October 17th, 2007 at 8:22 am
AndreH,
There is no question that stars can be photographed in the lunar sky. The problem is photographing simultaneously with the bright lunar landscape, astronauts, etc. The exposure settings for one are not optimal for the other. Notice, please, that there are no stars in photographs taken from the space shuttle under similar conditions. Under conditions optimized for star imaging, they can be photographed. Star imaging is in fact routinely used by remote spacecraft for navigation.
Notice also that BA’s photo above was taken well after the Sun had set, and that there are only a very few of the brighter sky-objects (the Moon, Jupiter, Antares) registered on it. The many other stars in that field of view didn’t show up at all, because the exposure wasn’t adequate to register them.
October 17th, 2007 at 9:57 am
Rob asked: “Also BABlogger, how did you know that the moon had dipped a far as it could go based on its positioni vi a vis Jupiter?”
Because as Phil says: “The Earth orbits the Sun (with me so far?). Over the year, that means it looks like the Sun makes a big circle in the sky relative to the stars. We call that path the ecliptic. The major planets all orbit the Sun in roughly the same plane, so they stick to the ecliptic too. Not exactly on it, but pretty close.”
This means that the position of Jupiter is roughly equivalent to the ecliptic, and if the moon was 5 degrees below Jupiter, then it was 5 degrees below the ecliptic – meaning it was as far down as it could go.
October 17th, 2007 at 10:06 am
AbdreH: “…You can’t see the Sun and stars in full daylight…”
Obviously you can see the sun in full daylight. After all the Sun is what makes it daylight. But I think I know what you mean.
Reminds me, though, of the woman who said, “If the Sun is a star how come you can’t see it at night. ” And see was serious!
October 17th, 2007 at 10:09 am
I’m curious, and you might answer this in a later post… I recall in school that one of the theories of the Moon’s formation was that it somehow ’spun out of the Earth’ (I think that’s pretty impossible) or was the product of a collision with the Earth (more probable?).
If so, I’d expect the Moon to orbit in a plane with the Earth’s equator, but since we know that’s 23.5 degrees (from an earlier post, if we forgot it from science class) off the elliptic, if these theories were true, wouldn’t we expect the Moon to orbit just as far off the plane as our axis?
So I guess I’m curious if the prevailing attitudes about the formation of the moon have changed, and why 5 degrees, not close to 0 or 23.5.
October 17th, 2007 at 10:27 am
My brother works in TV (on a certain BBC Wales show, in fact, which is cool but even further off-topic) and they absolutely hate having to do night scenes. Why? Because they have to make the sky look starry (because that’s what the viewer expects) when you can’t actually see any stars at the exposure times they use!
October 17th, 2007 at 10:42 am
>>> Back on topic…. BEAUTIFUL. Our universe is so beautiful.
Well… most of it…
http://www.midwestrocklobster.com/ugly/ugly3_lg.gif
Yes, it’s real. Won the Ugliest Dog contest somewhere. Died recently.
October 17th, 2007 at 1:05 pm
I stumbled on this blog a few weeks ago & thoroughly enjoy it. I am not an astronomy buff but a fairly well rounded, intelligent diverse individual with a strong leaning towards metaphysics. Some of the statements seem obvious and the banter can get far flung. Thanks for all of it.
October 17th, 2007 at 2:20 pm
“t is as though our Moon is taking its marching orders more from the Sun than from the Earth. This, and the fact that the Moon’s path around the Sun is everywhere concave toward the Sun (also unique?), make it reasonable to call the Earth-Moon system a double planet. (These and the relatively small planet-satellite mass ratio, 81.3, which until Charon was discovered, was by far the smallest of any known planetary satellite in the solar system.)”
The Earth-Moon may be considered a double-planet, but only because of their mass-ratio, not because the “Moon is taking its marching orders from the Sun”. The latter is entirely due to the fact that the Moon’s orbit is quite large and its orbit is in fact strongly perturbed by the gravity of the Sun. Indeed, consider the irregular satellites of the Jovian planets: all of these irregulars “take their marching orders from the Sun”, and yet we would not consider, say, Jupiter and Paisphae to be a double planet. In general, irregular satellites have inclinations (measured w.r.t. the planets’ orbital plane) that are far from zero. The Moon’s 5 degree inclination is indeed quite large.
Cheers.
October 17th, 2007 at 4:20 pm
Stephanie:
Cheers, that had me confused too.
But that only works if you’re far North, correct? e.g. If you live near the equator, the ecliptic is an arc over your head. Then the Moon, when it’s furthest South, would appear to the left of Jupiter?
October 17th, 2007 at 4:28 pm
seonaidbarrett
As I recall (and I may be wrong here – operating from fuzzy memory) the prevailing theory of the moon’s ecliptic tilt is that the moon was indeed created by a massive impact into the then very young and hot Earth. This impact was from a large object with a different ecliptic than the Earth. Think of a comet orbit. The ejecta from the impact (the moon) achieved orbit of the Earth – and since the impactor was off ecliptic the ejecta was as well. The 5 degrees is just concidental… it could have just as easily been 25 degrees. It’s like a game of billiards (only in 3 dimensions) – in order for a ball to go straight you have to hit it perfectly through it’s center. if you are off by just a bit the target ball is propelled to one side or the other.
Not sure I’ve been terribly clear there. Sorry if I’ve muddled things up.
October 17th, 2007 at 11:26 pm
Moon photos and stars:
http://en.wikipedia.org/wiki/Examination_of_Apollo_moon_photos#There_are_no_stars_in_any_of_the_photos
October 18th, 2007 at 12:54 am
Thanks, Kristin. I’m familiar with the analemma and what it represents; the ecliptic was a new concept to me, and I didn’t get a clear understand of what it was from this post and how it related/differed from the analemma.
Phil said the sun makes a big circle in the sky over the course of a year, called an ecliptic. The analemma is the path that the sun takes over the course of a year at a fixed time of day, and this is clearly not a circle (as seen in several APOD photos). So I remain confused, but not yet to the point where I’ll look it up, as I’ve been working for over 20 hours now and it’s time for bed.
October 18th, 2007 at 2:05 am
Johnny Vector
Thanks for the explanation, now even I got it. What really puzzled me, I think, is the off-hand way the statements about the sun moving through the stars in the course of the year are usually made. To me it sounded like something totally obvious, something you can really see day for day (like the sun rising and setting or the stars moving in an arc across the sky at night), when in reality it is a rather abstract concept (at least to me), that can not easily be observed (meaning “be looked at”) from earth.
October 18th, 2007 at 2:51 am
BA, that’s not a bad pic. Can you tell us the length of the exposure please?
I recently bought a new camera (my first digital, woohoo!), and its maximum exposure is 60 seconds. I tried this out (first light, I guess) recently, and got a reasonable pic of Ursa Major with the camera set to wide-angle, but zoomed in (12x optical zoom), all the stars were curved lines. I had not realised that the 0.25 degrees the Earth turns in a minute would be enough to streak the stars across my image.
For a typical camera (say with a 35 mm objective), is there an optimal compromise between exposure time and keeping the stars as point-like sources (assuming perfect seeing)?
October 18th, 2007 at 5:19 am
Tailspin:
“AbdreH: “…You can’t see the Sun and stars in full daylight…â€
Obviously you can see the sun in full daylight. After all the Sun is what makes it daylight. But I think I know what you mean.”
Sorry, but in did not say this.
Mark Martin:
“There is no question that stars can be photographed in the lunar sky. The problem is photographing simultaneously with the bright lunar landscape, astronauts, etc. The exposure settings for one are not optimal for the other. Notice, please, that there are no stars in photographs taken from the space shuttle under similar conditions. Under conditions optimized for star imaging, they can be photographed. Star imaging is in fact routinely used by remote spacecraft for navigation.
Notice also that BA’s photo above was taken well after the Sun had set, and that there are only a very few of the brighter sky-objects (the Moon, Jupiter, Antares) registered on it. The many other stars in that field of view didn’t show up at all, because the exposure wasn’t adequate to register them.”
Thanks for the explanation. But I knew this already. I tried to be ironical.
I was really surprised Jupiter can be seen on the photo although the moon seems to be some magitudes brighter and bigger. Therefore my thinking was mayby some HB may claim this.
Andre
October 18th, 2007 at 9:57 am
“Thanks for the explanation. But I knew this already. I tried to be ironical.”
Ah, I understand now. Please accept my apologies.
October 18th, 2007 at 5:45 pm
Thanks for saving me from looking this up myself, Phil! I was driving across town last night at about 9:30 at night and saw a very low crescent moon (at the stage between “New” and “First Quarter” that I call the “Cylon Moon”), and noticed that it was positioned much farther to the South than I’m used to seeing. I knew the 2007 edition of the Old Farmer’s Almanac has a good article on “high” and “low” moons for the year, and I meant to look it up to see if we were at a “low” extreme. Now I don’t have to!
October 19th, 2007 at 12:09 am
Mark Martin: “Ah, I understand now. Please accept my apologies.”
No one has to apologise for the truth!
Sometimes it seems (for what reason ever) that irony is not detected when I try. Maybe as a non native English speaker I don’t get the correct twist.
Andre
October 19th, 2007 at 10:29 am
I have developed an annual planet calendar – http://www.bautforum.com/questions-answers/65218-venus.html#post1077662. For 16 October it shows that Moon was conjunct Jupiter, and half way between the lunar nodes. This is a quick rough and ready method to check main planetary ephemera.
October 20th, 2007 at 7:08 am
I was never looking at stars this way – like you do! It’s great!
October 20th, 2007 at 8:41 pm
Phil Plait’s point was that we could see that the Moon and Jupiter were about five degrees apart (north-south) because their conjunction this month was square to the lunar nodes, when moon is furthest from the ecliptic. Coming up on 3 and 4 November, we can see the conjunction between the Moon and Saturn will be exact (ie on the ecliptic) because Saturn is conjunct the South Lunar Node where the moon crosses the earth-sun plane. I am not sure if it will be an occlusion. In my previous post I linked to the BAUT thread where we discussed this. The direct link to the image is http://www.bautforum.com/attachments/questions-answers/6359d1190861952-venus-2007-planet-calendar-dates.gif. I am now producing an update calendar for 2008. Inclidentally, I live in Australia, and for us Antares is to the left of Jupiter as they set, not to the right as in Phil’s great picture. And another thing, the linked image shows how Jupiter is tracking to a Christmas link up with the Sun, Mercury and the planet whose name we dare not speak.
Daphne – assuming you were talking about my picture, the reason you have never looked at the stars this way is that I invented it.
October 21st, 2007 at 6:14 pm
Correct link is http://www.bautforum.com/attachments/questions-answers/6498d1192937205-venus-2007-planet-calendar-dates.gif
March 9th, 2009 at 6:03 pm
this is soooooooooooooooooooooo georgious and awesom
March 9th, 2009 at 6:04 pm
if i were to see something like that i would freak! <3 Josy