Green Baron

A wise decision !

Can't check it any more. Ran out of money and had to sell the boat (including dinghi) :-/

This is of concern for sporty sailing boats and anything that shall move without too much friction. They know quite well what happens at the limiting layer between laminar and turbulent flow. Sailing boat construction, manufacturers of antifouling paint, profiles of sails and aircrafts, there is where i would start to search .... but i am an ignorant in these things. Edit: a desert doesn't keep Australians in Alice Springs from performing a boat race. Though cavitation only plays a role later the day when satisfying thirst :-)

I don't think it does. The dinghi propeller did (a 2.5hp suzuki). The 3 blade folding prop of a volvo penta 75hp of a 43ft Hanse did not. Your ego is safe :-))

Sure, give it here :-) I didn't expect the effect takes place at slow moving propellers as well. I never attributed the bubble spur behind the (plastic !) dinghi prop as cavitation. The 3 blade folding prop of my sailing boat never showed that, but max rpm was 2000/min (which i never really used).

Ok, but the passenger- and merchant ships don't rely on such things ? I read the moving parts wear off quickly. Ferries here are only taken out of the water after impact into harbour walls :-)) The fast multihulls that operate here have diesel engines and water jets.

I know the effect plays a role in river rafting and canoeing behind a step or waterfall, in combination with dynamic movement of water. It might be that mixing of water and air by the propulsion reduces the lift capacity of water. The waters behind fast ferries that run 35+ knots don't look calm at all. Whether it's enough to drown a person, idk. On the other hand, the foam may be only superficial as engineers probably try anything to keep the propellers/jets fully submerged at all times efficiency wise ... Edit: not cavitation, that was simply about mixing of air/water by dynamic movement. Cavitation is, as far as i know avoided as far possible. If at all it only plays a local roll at the blades of propellers, i would guess.

I do not understand everything of the question. The concept of a "surface" doesn't apply to a gas ball like the sun, the density rises when coming closer. The photosphere, that visual "surface" has a temperature of 4-5000K, so solid abjects from whatever real material are probably vaporized. If it sinks into the chromosphere the atoms would be turned into a plasma. If you want to "drop" something from earths orbit you have to get rid of the orbital speed, +/-30km/s. Either according to Hohmann or by performing several swing-by maneuvers behind other orbital masses until the AP is low enough that the gases of sun's outer atmosphere will perform the rest. So the initial "small push" has to be at least strong enough to bring it behind another orbital mass (suggestion: Jupiter, he's good for a lot of things :-)) to initiate a series of swing-by(s) to drop the AP. Jupiter transfer can be made cheap, i think (a few km/s), that's the smallest initial push i could imagine. I would guess that by the high orbital speed of an object, coming down all the way from Earth's or Jupiter's orbit, would be destroyed by friction in the gases surrounding the sun long before it comes close to the photosphere. If you mean by "dropping" to decelerate the object from 30km/s to 0 relative to the sun and then wait you'll end up with a terminal speed "dive-in" speed of 30km/s (how comes :-)). If you give it "decent push" initially (to get behind another mass to initiate a swing-by series) you'll end up with 30km/s +/- decent push. Is that correct ? Edit: not considering any friction in interplanetary gases or near the sun

Looks sturdy. Am curious, since i do not have any experience with an alt/az mount. Do you plan long term exposures ? If so how do you plan to cope with the rotation of the field ? Do you plan to put some sort of equatorial wedge (German "Polhöhenwiege", took me 3 min to find the translation :-)) under it ?

psst .. take Fomalhaut or Elmuthalleth or Shurnarkabti Shashutu

Gosh, they should have equipped Schiaparelli with a flagpole on one side and a stick with a shoesole on the other. Just to settle the matter with all due imprint :-)

That's two and a half years ahead. I think the 2018 moon trip is already ambitious. I hope they can find a sink for the money that makes more sense. Like another vlbi capable big fat telescope.

Yes, the effect is for an ocean ship moving at some speed. A maneuvering or slow moving ferry or a small sailing boat does not have an expressed wave system. The small sailing boat because is too small and usually doesn't move at its hull speed under engine and the hull is normally very effectively streamlined. A small motorboat usually leaves it's wave system and pushes itself on the bow wave. Also the small to tiny propeller eventually might hurt you (even badly) if you get in contact with it but it will not kill you. People falling overboard on the open waters usually are not found any more. These are more than might think, quite few every year, more from recreational boats than huge ships. People falling overboard in harbour areas have a tiny chance, if it is not by night. But often times you read or hear the SAR messages on the information systems (NAVTEX) for a few hours and then they are canceled. If you want to learn more i'd suggest you take a look at the reports of the various marine accident investigation boards. :-) Edit: how strong the Bernoulli effect can actually be is best shown by accidents in narrow canals or tidal streams ways, were even huge ships can collide just because the effect attracts them until contact if not counteracted in time. Editedit: and accidents between small boats and swimmers/divers sadly happen very often ! Normally beaches and swimming areas are separated from the open water by a chain of yellow buoys signaling that no boat traffic is allowed. Sometimes channels, marked with a red and green buoy signal a narrow path for dingies or diver boats when there is an anchorage nearby.

Hi, there are different effects at work. Let's assume open water, that makes it easy. In a canal or a narrow things get complicated. Also a boat that leaves it's wave-system (gliding/surfing etc.) is a different thing. So, the clear answer is: it depends (where you fall in) ! Have a look at the waterline of a moving boat: there is overpressure at the bow, shown by a wave the boat pushes in front it. Water then accelerates along the hull, and according to Bernoulli (or so) the pressure sinks, as shown by a long 1/2 lambda "negative" wave along the waterline. At the stern there is underpressure and turbulence, "sucking" the boat backwards. Additionally there is the propulsion, usually a (or more) propeller that shoves water from front to back thus pushing the hull through the water. So if you happen to drop in the first third of hull of a long boat you are probably pushed away by the water. If you happen to drop in the under pressure area where maybe the suction of the propeller helps you have a good chance of having fun in the Great Roundabout. If you hop off near the stern you'll probably just hit the hull and then be left behind, reflecting over the future and your family having fun with your life insurance. Me as a hobby sailor tells you: falling overboard is almost sure death, because if no IMMEDIATE (seconds) action is taken you will not be found again. Water temperature and quality of the life vest determine how much time you have left. A "person overboard" is an emergency and reason for an immediate distress (aka "Mayday"). :-) Edit: partly ninja'd by @kerbiloid Second edit: i mean, of course, a quiet inland lake is another thing like a journey on the open waters.

Bode's alone is a little too small for the fov of my telescope/camera without reducer (1.3°*1.0°). But the couple M81/M82 will fit nicely. @munlander1: Calculate the field of view of your scope/camera combination. Image size of the scope is a function of focal length, while the size of the chip determines how wide an angle of that image it actually sees. The size of the pixels determine the resolution (together with the scope's resolution and the the seeing conditions of course). A quick search will show you the formulas. You might discover that with 1m focal length and an aps-c chip you might have something in the range of 1.6°*1.3° (not calculated just pi*windowframe !). It seems like the grid in the overview is 1° wide (?), so you can estimate of what you'll see with your scope/camera combination.

I must say that i am disappointed about what happened in the other thread. It is not the march that has a bad notion, it is people that dispute and get mad at each other over details while totally ignoring or forgetting about the big picture, the cause for the march in the first place. A few are enough to disrupt a party of many. I surely have (re-)learned a lesson and I kindly ask to reflect about this. For those who are interested, there are more activities announced for the course of the week, and a wikipedia article has been written. Please do not derail this thread as well :-)

An funny accident (video): https://www.youtube.com/watch?v=Ti-zq4azB_8 Happened in the harbour of Las Palmas de Gran Canaria on friday. I know the harbour, have been there many times when sailing the Canaries. According to preliminary information the boat suffered a complete power loss as it had just left the harbour basin and was turning around in a sharp curve towards the north when that happened. Apparently rudder wasn't functional and it took a few seconds to switch the engine to backwards (they have, of course a gear for switching directions). Short after impact it then runs backwards s you see by the propeller water. You can see the dimensions in comparison to the car that luckily passed a few seconds before impact. 180 were on board, 13 persons suffered minor wounds, mainly bruises, one broken clavicle. Sad thing: 60.000l (The decimal is thousands. Savvy ? :-)) of diesel ran into the sea as the diesel supply to the berths was cut by the impact. As was a tube of a water desalination plant, so the city is a little short on fresh water now. 30.000l were pumped out directly by salvage crews, the rest is assumed to evaporate over the next days. The carpet is confined to an area of 3 by 1,2 km along the coast. "Phew" :-) Edti: just watched the video another time with a friend and he asked "Why didn't they drop the anchor ?". They did, one can see the chain tight as a string, but the water is deep and rocky (around 40m) and the angle bad. The anchor could not dig in and thus only served as an additional means to lower the speed.

Correct in my eyes. Problem is, we do see more and more tries to actually force people into believing and diminish the role of science. But in the end it's not belief that keeps people healthy and alive and fed and it's not belief that leads to new discoveries. Nor is it exertion of influence, which can only limit the work of scientists, not broaden the view. That's why i find these marches important. But, of course, as any scientist, i might be wrong. But i need arguments to change my mind :-) Edit: oh, btw., some geoscientists actually copied their work to private machines a few months ago. They seem to be in a diffuse fear that they might need a backup in a few years.

The personal freedom is corrupted when anyone tries to tell you how to interpret something or keeps you from thinking what you want or channels the information that reaches you. Science does not do so, in contrary it encourages people to question even the own findings and share them with others to come to a conclusion that a majority can accept. It has its rules, which are open and do not change (edit: every legislation period). Modern philosophy tells us to use reason to come to our findings and not to just put forward claims without a chance to prove or disprove. The former views on of cognitive sciences have been replaced by Empirical Falsification and Critical Rationalism.

I gave asylum to this little stray killer machine. After a few months roaming around the house we went to cure the parasites and now it apparently is quite relaxed ... Only sometimes i have to clean after it, mainly partly devoured lizards that lost the ability to escape after gears were chewed off or mice that escaped between the furniture. Dead mice deposited in front of the bedroom door are meant to be presents and the cat deserves a commendation. Hair on the keyboards is a very minor problem.

I already started a thread about this a page down: I totally agree with @PakledHostageHostage. Science is highly in danger of being exploited by politics, denied when it contradicts short term gainings, regulated to yield intended results and bent by certain groups who want to gain influence on education. I read the concerns in the journals every week, though these are mainly about recent changes from politics and those that are still pending. The journal Nature expressed the concerns that the US will loose the connection to research in fields such as earth science and renewable energies and thus might not be as good prepared for the changes that are to come. So i too think it is a necessity. Unfortunately i failed lately when i discussed with an elder women who was totally convinced that Ptolemaios' view with the earth in center will have a revival soon and one day we shall all see. I was not able to convince her, reflecting over facts just wasn't her strength :-)

Its on my list.

Another game (factorio)is short before an update. Devs showed the upcoming new stuff in a news-thread yesterday. Now people go crazy and demand a higher price for the game as the fun/price ratio is too low. These are strange times we live in my friends ...

Oh, well, discussing this deeper would violate forum rules :-) I hadn't heard of it before. If were in the area i would have a look and see if it serves a purpose. Since they explicitly call for people who actually do work in science and might discuss their work openly makes me think it is peaceful and serious.