Starship Asterisk*

Multicolor Venus

Explanation: Brilliant Venus now shines in western skies at twilight. Seen as the prominent evening star, the planet is a tantalizing celestial beacon even for casual skygazers. Venus can offer less than satisfying telescopic views though. The planet is shrouded in reflective clouds that appear bright but featureless at the eyepiece. Still, careful imaging with a series of color filters, as used in these composite images, can reveal subtle cloud patterns. Captured early last month from a backyard observatory in Manchester, New Hampshire, USA, the images are based on video camera frames. The data was recorded through near-ultraviolet, green, and near-infrared filters (left), and red, green, and blue filters while Venus stood high above the western horizon just before sunset. This season's evening apparition of Venus is the best one for northern hemisphere observers in 7 years. It will ultimately end with a solar transit of the planet, the last one to occur in your lifetime, on June 5/6.

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Pardon our ignorance, but what makes Solar transits of Venus such a rare(ish) event ?
Clearly the orbits of the Earth and Venus play a part, but is there more to it than that ??

Ron wrote:Pardon our ignorance, but what makes Solar transits of Venus such a rare(ish) event ?
Clearly the orbits of the Earth and Venus play a part, but is there more to it than that ??

http://en.wikipedia.org/wiki/Venus_transit wrote:

[b][color=#0000FF]Diagram of transits of Venus and the angle between the orbital planes of Venus and Earth[/color][/b]

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<<Venus, with an orbit inclined by 3.4° relative to the Earth's , usually appears to pass under (or over) the Sun in the sky at inferior conjunction. A transit occurs when Venus reaches conjunction with the Sun at or near one of its [early June or early December] nodes, the longitude where Venus passes through the Earth's orbital plane, called the ecliptic. Although the inclination between these two orbital planes is only 3.4°, Venus can be as far as 9.6° from the Sun when viewed from the Earth at inferior conjunction. Since the angular diameter of the Sun is about half a degree, Venus may appear to pass above or below the Sun by more than 18 solar diameters during an ordinary conjunction.>>

Venus; one hot planet! Also thought to be the Goddess of Love!

Looks like Neufer and Orin got their post swapped this morning.......

FloridaMike wrote:
Looks like Neufer and Orin got their post swapped this morning.......

Frankly, I don't believe in Stratford upon Avalon.

Have these images been flipped on their vertical axis? From earth at this time of year, I would have expected to see the bright side of Venus on the other side. If I am in the northern hemisphere facing due west, the Sun goes down slightly to my left and Venus is up in the sky farther to my left. It seem like the side of Venus facing the sun should be the right side and pointing down slightly which is not what these images show. Thanks for any feedback.

I note that the parts of Venus that are brightest in ultraviolet light are the least blue, or rather the most red, in UBV. How weird. (Or are we seeing Ha emission here?)

Ann

It may not be the last time for everyone. For example if a child at his ten follow apod and see the transit, then it's possible that he may live to his 115 and watch the next transit of 2117

I really like this APOD. It's time for Venus to get some attention. Venus is approaching its maximum brightness at crescent phase, the less illuminated the bigger the apparent diameter and the brighter the planet is. By May Venus will be really bright and slim, a beautiful sight. And it's a great time to experiment if the famous Ashen light is real or not.
Venus usually favous the south hemisphere observers but this is the northern venus trip in many years. Including a visit to the Pleaiades.

luigi wrote:Venus usually favous the south hemisphere observers but this is the northern venus trip in many years.

I don't believe it is accurate to say that Venus favors either hemisphere. At any given time, its declination will place it north or south, but over any significant period it spends an equal amount of time favoring both hemispheres.

Chris Peterson wrote:

luigi wrote:Venus usually favous the south hemisphere observers but this is the northern venus trip in many years.

I don't believe it is accurate to say that Venus favors either hemisphere. At any given time, its declination will place it north or south, but over any significant period it spends an equal amount of time favoring both hemispheres.

Are you sure Chris? I had the idea that Venus is on a southern declination most of the time as Mercury is (I'm sure about mercury) but maybe my thinking was wrong

Wouldn't b e a gas if Pluto also had an atmosphere ?

The transit of Venus is an important event.
The alignment with the Sun and the Earth must have a impact our planet atmospheric.

nuclearcat wrote:It may not be the last time for everyone. For example if a child at his ten follow apod and see the transit, then it's possible that he may live to his 115 and watch the next transit of 2117

While possible, it is extremely rare. There are only 27 known people worldwide that lived beyond 115 years of age (of which there is only one living today). Not only does one need to be alive in 2117, the eyes of the old watcher need to be in such condition at that age, that the event is watchable at all, or the transit of 2012 will still be the last one really witnessed.

Wolf kotenberg wrote:Wouldn't b e a gas if Pluto also had an atmosphere ?

Pluto does have an atmosphere- thin, but enough to be detectable, and to create a significant greenhouse effect.

luigi wrote:Are you sure Chris? I had the idea that Venus is on a southern declination most of the time as Mercury is (I'm sure about mercury) but maybe my thinking was wrong :D

I don't see how this could be, either for Venus or for Mercury. The planets all orbit on planes tilted some small amount with respect to each other, with a common intersection point at the Sun. So with respect to the Earth's orbital plane, the other planets must spend half their time above it and half below (ignoring the slight impact of orbital eccentricity). The only way I could see one hemisphere or the other having a better view would be if the planets were in orbital resonance with the Earth... which they are not. Certainly, there can be a sort of aliasing between the orbits, such that we cycle through periods where planets are higher in one hemisphere or the other, but I don't see anyway this could be the case over the long term.

Chris Peterson wrote:

luigi wrote:Are you sure Chris? I had the idea that Venus is on a southern declination most of the time as Mercury is (I'm sure about mercury) but maybe my thinking was wrong

I don't see how this could be, either for Venus or for Mercury. The planets all orbit on planes tilted some small amount with respect to each other, with a common intersection point at the Sun. So with respect to the Earth's orbital plane, the other planets must spend half their time above it and half below (ignoring the slight impact of orbital eccentricity). The only way I could see one hemisphere or the other having a better view would be if the planets were in orbital resonance with the Earth... which they are not. Certainly, there can be a sort of aliasing between the orbits, such that we cycle through periods where planets are higher in one hemisphere or the other, but I don't see anyway this could be the case over the long term.

Because of the seasons I think.
In the case of Mercury it is higher in the sky (maximum elongation) when it's early autumn and late winter for the south hemisphere meaning the skies are darker and we can see mercury for a longer time. I think it's very hard to see Mercury high in totally dark skies in the North Hemisphere but it is something common in the South hemisphere.

I'm not sure about Venus but I think it can be the same case?

Chris Peterson wrote:

luigi wrote:Are you sure Chris? I had the idea that Venus is on a southern declination most of the time as Mercury is (I'm sure about mercury) but maybe my thinking was wrong

I don't see how this could be, either for Venus or for Mercury. The planets all orbit on planes tilted some small amount with respect to each other, with a common intersection point at the Sun. So with respect to the Earth's orbital plane, the other planets must spend half their time above it and half below (ignoring the slight impact of orbital eccentricity). The only way I could see one hemisphere or the other having a better view would be if the planets were in orbital resonance with the Earth... which they are not. Certainly, there can be a sort of aliasing between the orbits, such that we cycle through periods where planets are higher in one hemisphere or the other, but I don't see anyway this could be the case over the long term.

From this Wikipedia article:
http://en.wikipedia.org/wiki/Mercury_(p ... bservation

"Mercury is more often easily visible from Earth’s Southern Hemisphere than from its Northern Hemisphere; this is because its maximum possible elongations west of the Sun always occur when it is early autumn in the Southern Hemisphere, while its maximum possible eastern elongations happen during late winter in the Southern Hemisphere. In both of these cases, the angle Mercury strikes with the ecliptic is maximized, allowing it to rise several hours before the Sun in the former instance and not set until several hours after sundown in the latter in countries located at southern temperate zone latitudes, such as Argentina and New Zealand. By contrast, at northern temperate latitudes, Mercury is never above the horizon of a more-or-less fully dark night sky."

Similar explanations for Mercury appear in the RASC Observer's Handbook and Guy Ottewell's Astronomical Calendar. The Wiki article doesn't explain why it happens, but Ottewell says "The reason is that the planet [Mercury] is then farthest out from the sun, near its eccentric orbit's aphelion, which is in the part of the orbit tilted southward in relation to the earth." Note that Mercury has a considerably higher eccentricity (0.21) and inclination (7.0 degrees) than any of the other planets (now that Pluto is excluded).

Venus has an eccentricity of 0.007 and an inclination of 3.4 degrees. I've never seen any reports of such a visibility asymetry for Venus.

Joe Stieber wrote:From this Wikipedia article:
http://en.wikipedia.org/wiki/Mercury_(p ... bservation

"Mercury is more often easily visible from Earth’s Southern Hemisphere than from its Northern Hemisphere; this is because its maximum possible elongations west of the Sun always occur when it is early autumn in the Southern Hemisphere, while its maximum possible eastern elongations happen during late winter in the Southern Hemisphere. In both of these cases, the angle Mercury strikes with the ecliptic is maximized, allowing it to rise several hours before the Sun in the former instance and not set until several hours after sundown in the latter in countries located at southern temperate zone latitudes, such as Argentina and New Zealand. By contrast, at northern temperate latitudes, Mercury is never above the horizon of a more-or-less fully dark night sky."

That's interesting. I was ignoring the eccentricity and inclination, but I guess it's enough to be significant in the case of Mercury, which never achieves a very great elongation. Of course, this relationship will still change with time... I guess it's just a few millennia, not years!

Venus has an eccentricity of 0.007 and an inclination of 3.4 degrees. I've never seen any reports of such a visibility asymetry for Venus.

I think that the low eccentricity and lack of orbital resonance means that there will be very little difference in observation quality between the northern and southern hemispheres.

The next transit is due on 2117 Dec 11 at 02:48 Universal Time. That's just typical, as I will likely be asleep at that time of night!

Perhaps if people alive now really wanted to see the next transit they could be put into a medically induced coma and be brought out of that in time. It's just a thought.

Chris Peterson wrote:

Joe Stieber wrote:From this Wikipedia article:
http://en.wikipedia.org/wiki/Mercury_(p ... bservation

"Mercury is more often easily visible from Earth’s Southern Hemisphere than from its Northern Hemisphere; this is because its maximum possible elongations west of the Sun always occur when it is early autumn in the Southern Hemisphere, while its maximum possible eastern elongations happen during late winter in the Southern Hemisphere. In both of these cases, the angle Mercury strikes with the ecliptic is maximized, allowing it to rise several hours before the Sun in the former instance and not set until several hours after sundown in the latter in countries located at southern temperate zone latitudes, such as Argentina and New Zealand. By contrast, at northern temperate latitudes, Mercury is never above the horizon of a more-or-less fully dark night sky."

That's interesting. I was ignoring the eccentricity and inclination, but I guess it's enough to be significant in the case of Mercury, which never achieves a very great elongation. Of course, this relationship will still change with time... I guess it's just a few millennia, not years!

On the (late summer) morning of March 3, 2008, Mercury (near aphelion) was 27.13º higher in altitude than (and west of) the Sun on the Tropic of Capricorn [ http://apod.nasa.gov/apod/ap080310.html ] (but only 19.23º higher in altitude than the Sun on the Tropic of Cancer).

On the (late winter) evening of Sept 10, 2008, Mercury (near aphelion) was 26.75º higher in altitude than (and east of) the Sun on the Tropic of Capricorn (but only 16.22º higher in altitude than the Sun on the Tropic of Cancer).

Chris Peterson wrote:
Of course, this relationship will still change with time... I guess it's just a few millennia, not years!

I'm guessing that it requires getting Mercury's perihelion to precess
into the Southern Hemisphere which is more like 100,000 years.

neufer wrote:

Chris Peterson wrote:Of course, this relationship will still change with time... I guess it's just a few millennia, not years!

I'm guessing that it requires getting Mercury's perihelion to precess
into the Southern Hemisphere which is more like 100,000 years.

Like I said, a few millennia. <g>

Chris Peterson wrote:

neufer wrote:

Chris Peterson wrote:
Of course, this relationship will still change with time... I guess it's just a few millennia, not years!

I'm guessing that it requires getting Mercury's perihelion to precess
into the Southern Hemisphere which is more like 100,000 years.

Like I said, a few millennia. <g>

• • King Henry VI, Part iii Act 4, Scene 7
  MONTAGUE: What talk you of debating? in few words,
  • If you'll not here proclaim yourself our king,
    I'll leave you to your fortune and be gone
    To keep them back that come to succor you:
    Why shall we fight, if you pretend no title?

What I was hinting at with my atmosphere on Pluto commentary was actually hoping not for an atmosphere so we can see something after New Horizons long trip. I would not shed tears if it crashes into Pluto, a la Ranger, and JPL gets fantastic close ups.