LOONNNGGG time watcher, first time poster.....

I was telling my 7 year old son about New Horizons (he was born on the one-year aniversary of the launch). He was particulary interested in the remoteness of Pluto and was astonished when I told him about how the sun is much less bright way out there on the edge of the solar system. Does anyone have a good practical way of simulating the lighting conditions out there? For example, is the amount of available light similar to the moonlight on a full moon night? Thanks

Sure- sunlight is about 1000x fainter on Pluto than on Earth (~32x further from the sun, and the sun's brightness goes as 1/R^2). That sounds like a lot, but the human eye is amazingly adaptable- we can see fairly well in full moonlight, which is about a million times fainter than sunlight.

Illumination on Pluto is something like ordinary subdued indoor domestic lighting like you might have at home in the evening. If you have a camera which reports exposures settings you can check this- for a pair of similarly-exposed photos, illumination of the scene is proportional to (f-stop)^2/(exposure time). ["^2" means "squared"]

[edit] As an example, if you expose an outdoor scene at 1/250th second at f11, and an indoor scene (with the same ISO) at 1/8th second at f2, the brightness ratio of the two scenes is about 950x.

John

The Sun would be a point, not a disc, but still be over 200 times the brightness of the full moon (an average, given the elliptical orbit).
Phil Plait has a good article on this:
http://blogs.discovermagazine.com/badastro...sun-from-pluto/

I believe it's about 250x brighter than a full moon. About 1/1500th as bright as the Sun at Earth.

Someone may want to check my maths on this....but....

One way to express it is with a camera. If you go outside with a DSLR and open the aperture fairly wide - you might get an exposure of, say, 1/4000th of a second ( the quickest exposure on many off the shelf consumer DSLR's )

Find a place where the same aperture results in an exposure of about 1/3rd of a second. That's how much darker it is on Pluto compared to the Earth.

Alternatively - it's like going from an aperture of F2 to F38....but without the added benefit of great depth of field

Doug

I guess, you intended to write "F1 to F38".
For the other values I got about the same.

Yeah - I as thinking of my 50mm F1.4 - but rounded up

A good way to simulate the brightness of the sun at pluto imho is when a solar eclipse at earth comes close to the totality phase.
I think about 15 to 10 minutes before totality arrives is just about the same brightness level at pluto..but this is only rough guess and depends on the eclipse geometry.
Could one do the math for this please ?

Shadows during this eclipse phase on earth are strange because of the thin sun sickle..shadows at pluto must be still more sharper with almost no penumbra visible.


Robert

I have on just a couple of occasions managed to observe shadows cast by Venus. They are very faint because of course the surface brightness of Venus is thousands of times less than the Sun. But they are also very sharp, making the shadows of near and far tree branches impossible to distinguish. In terms of angular size our Venus is about the same as Pluto's Sun.

With a month of 29.5 days and an angular size of 32' for Sun and Moon, I get 3.2 seconds before/after totality to reduce brightness by a factor of 1500:
29.5d * 32' * 4 / 360° / 1500 / pi = 3.2 s.
(The dependence of the area of the visible part of the Sun from time should converge towards linear near totality in this idealized case of zero totality time, 2nd order equivalent to a horizontally shrinking rectangle with constant height 32'. A circle (area r²pi) is a little smaller than a circumscribed square (area 4r²), therefore the factor 4/pi.)
It's a little longer before/after totality for a larger angular size of the Moon, but further detail would be off topic in this thread.

A fun experiment would to be get a room and cover the windows so that only 1/1000 of the area is window is uncovered. That would give an idea of how bright it would be inside a house anyways.

In terms of a total solar eclipse I agree with Gerald it would be just a few seconds before totality. The exact time depends on the eclipse and the relative sizes of the sun and moon. Even then, the scattered light from outside totality would alter things. I have programmed some empirical formulae to get the sun's brightness depending on the eclipse magnitude (fraction of solar diameter covered), and the relative sizes of sun and moon. I'll try and locate them.

There would also be a time during daily twilight (say on a clear day) when the overall illumination of the ground would be 1/1000th of daytime. I'm guessing it would be about 30 minutes after sunset, with a solar elevation of -6 degrees.

The window experiment also sounds interesting. On a clear day the sky (without direct sunlight) has roughly 10% of the sun's light over the hemisphere. That would be over 20000 square degrees. Therefore if you have a window showing 200 square degrees of sky and no direct sun it might work. The diameter of the window would be about 15 degrees then, so one could stand about 4 times the width of the window away.

...yet another way to look at it: about as bright a full moon expanded to around 8 degrees in diameter.

I moved a bunch of posts to this thread from the old main NH thread.

This thread will be the main thread for what remains of NH's cruise phase (an amazingly short time really, I feel as if NH was recently launched but there are now almost 9 years since it was launched).

Today's awesome PPOD pic is at http://www.boulder.swri.edu/ppod/

Soon you can sign up for push notifications....

And EVEN BETTER! Here's Amanda's latest Postcard from Pluto! http://plutopostcards.tumblr.com/post/9817...itous-things-to …

Enjoy!

PPOD/Pluto Picture of the Day now has an indexed archive! http://guinan.space.swri.edu/nhepo/archive_index

PPOD now allows you to sign up for push notifications. http://www.boulder.swri.edu/ppod/

Hey Alan, you've indicated before that the data from the Pluto flyby in July 2015 will trickle in slowly. Will we still get to see high res images come in as the approach happens or will we have to wait a bit?

I read an interview (somewhere, don't have the link on me!) where the plan is basically that some images from around CA (those worthy of being under the newspaper headlines) are going to be given priority in the downlink sequence. So although it will take ages to get everything down, there won't be a second agonizing wait for the best stuff after July.

Every LORRI image that comes to the ground will be posted to see, with <24 hour delay. (LORRI is the hi-res imager). That will include the very best images we have at P-2 and P-1 days. After C/A, more and more will be downlinked as the bird spends increasing time downlinking v. gathering data. The full data downlink will take 16 months, but you will be along for the ride with us on approach, and on departure.

Interesting to see the PPOD 9/28 artist view, in light of the earlier discussion of the 1/1000 Earth illumination appearance.

http://guinan.space.swri.edu/nhepo/archive/2014/09/28

One might consider some of the assumptions of atmospheric parameters that would go into such a visualization. This includes optical depths of gas and aerosols, as well as their scale heights. The vantage point of the viewer above the mean terrain height helps the depiction of the surface haze layer.

Awesome, thank you. I can't wait!

Reddit AMA with the New Horizons team, - Q&A by Alan Stern et al. with space enthusiasts

http://www.reddit.com/r/IAmA/comments/2igk...s_new_horizons/

This is the first of 10 Infographics being produced for the mission in 2015, thought UMSFers would like seeing it hot off the press!

Looks great Alan! Getting so excited to see Pluto and Charon and the rest of the gang in the windshield.

Very nice, Alan. Thank you for sharing.

What blows my mind, is that, I don't think most people realize that we will be the first humans to ever see Pluto. Man, just thinking about that is crazy.

You should have been around for the Voyagers spacecraft, and the first close-up views of so many planets and their moons. Completely new landscapes on a yearly basis that had never been seen before by any human in history. You are right. It is mind-blowing!

considering i had just turned 10 by Aug ( v2) and sep (v1 ) of 1977
when the Voyagers launched .....
that era was a "time"

the 1976 things and goings on
Viking
Voyager
some of the Mariner missions

All the astronomy books i could get my hands on were being OUTDATED by the time that a 8 to 12 year old could read them

Been seeing new worlds for the first time since Mariner 9.

Never, ever gets old. Not even a little bit.

Went to Pasadena from France on a B707 to be part of Planetfest 89 for VII Neptune encounter...was to be the last for a loooong time...and here we (nearly) are. Thank you Mr Stern and All...

Climber, all- We can;t wait to bring this too you, and to everyone, everywhere... fasten your seat belts!

-Alan

2016 -2017 (like 1990 -1991) should be a great time for bringing out books on the solar system.

Is there going to be another planetfest like gathering for the Pluto flyby?

I'm sure there will be.
Here in Australia, back in the day, Voyager was making its flyby through the Neptunian system.
Our ABC (Australian Broadcasting Corp) had a 2 hour special.
It was evening over here in Western Australia and we had a special public night (Monday) to
view Neptune, btw, I'm a member of the Astronomical Society of the South West.
So there we are, a tiny blue disc in our telescopes, and on the TV some mind blowing images of
Neptune.

I've only seen Pluto once via telescope, a 12.5" f6 Newt (superb optics btw). A dot amongst dots.
So much looking forward to the flyby. Shame we don't have the delta V for orbit.

KBO targets for New Horizons (other than Pluto and Charon, of course) found!
http://hubblesite.org/newscenter/archive/r...s/2014/47/full/

Question - would the major targeting for such an object be done post Pluto system flyby, or (more propellant efficient, but perhaps more disruptive?) by tweaking the flyby parameters for a gravity assisted course correction?

Airbag

After the flyby. The science plan for the encounter is locked and loaded.

Emily is correct. And in addition, we're doing the optimal Pluto system encounter, so we would not degrade it even if we could for the KBO targeting.

So, rough back-of-the-laptop calculation has a cruise time to KBO encounter of ~3.5 years. That's assuming constant speed, ~1 billion miles further to go. Here's to hoping a few more pop out of the woodwork!

Wonderful news and big congratulations to the team.

Does 'definitely reachable' mean the target(s) can be approached arbitrarily closely? Can we look forward to seeing the selected one in as much detail as Pluto and Charon?

EDIT: My question already answered by Emily http://www.planetary.org/blogs/emily-lakda...-has-a-kbo.html

To summarise - Yes, close range is well within reach fuel-wise, but because the target's orbit will not be as accurately determined as Pluto's it will be harder to optimise the flyby distance perfectly for science.

What would have been my next question is also answered. The definitely reachable target is a cold classical KBO.

Terrific news! Congratulations to all the team for their indefatigable efforts in finding a candidate KBO.

I can't imagine that funding for a mission extension will be too hard to negotiate come the time

A little early for image sequencing discussions perhaps, but assuming the object's orbit can be determined accurately enough, is NH capable of undertaking 'skeet-shoot' (as per Cassini at Enceladus) techniques for very close imaging, given the low-light levels and relative speed at closest approach?

Well I have to say it ...

I always had faith in them.

www.unmannedspaceflight.com/index.php?s=&showtopic=2048&view=findpost&p=37681

Congratulations!

We'll soon see how similar Pluto is to Triton (or not as the case may be). Exciting times indeed.

May have to delay that textbook by a couple of years!

I asked Alex Parker about the possibility of searching for scattered disc objects:

They would most likely need to apply for Hubble time again. When someone inevitably writes a book on New Horizons they will have to mention the invaluable amount of help Hubble has done for the mission.

Mag 26.8 for PT1 ... according to Wikipedia, visible from 8m telescopes? They don't need hubble exclusively to track it?

I meant if they wanted to look for a scattered disk object like SFJCody suggested. Not PT1.

Incidentally, which telescope do you think would be able to find KBOs better, Hubble or the Webb?

We will probably try to track these guys from the ground. From our ground-based search campaign, we already have a huge amount of data covering the locations of these objects, from 6-meter and 8-meter telescopes, going back to 2011. These KBOs are too faint to have been *discovered* in those data, but now we know where look, we might be able to *recover* them from the images, and thus extend our knowledge of their orbits. We'll be working on that over the winter, and will also be considering future ground-based tracking observations. Future ground-based tracking won't be as precise as Hubble's, but may provide a useful supplement and backup to Hubble- we'll see.

John

John, this is probably a very premature question, but if JWST launches as currently scheduled could it too play a part in final pre-encounter position & size observations of PT1? Main reason I ask is that STScI is to be the controlling organization for both scopes, if I'm not mistaken.

Yes, quite possibly, *if* it launches in 2018- we certainly won't be counting on it! Keep in mind, of course, that PT1 isn't necessarily our final choice- the other two are still in the running.

John

The NH final wakeup coverage is live now here. (began 0200 GMT/7 Dec)

EDIT: Also, here's a link to Eyes On The DSN. DSS43 at Canberra is currently listening for NH.