OT: Falcon heavy rocket launch

[Mike Hunt]

Yeah, an immigrant sucking up all the benefits he can get.

[T i m]

That doesn't explain how it's 'now' ok though does it? It's not something they can easily re-run? ;-)

I think someone just picked up the same feed twice .

That seems to happen just as it's approaching some clouds (so my first thought was water droplets) but I guess it could be whatever was supposed to be burning, assuming it wouldn't have all evaporated at that speed?

Cheers, T i m

[Tim Streater]

Like Jezza.

[Tim Streater]

It's too bright in general. People asked the same Q about Apollo moonshot pix from the Moon's surface.

[T i m]

So was it just that the Roadster was on the 'day' side of the earth so it was too bright to see *anything*?

Amazing to think you can see celestial bodies (other than our sun of course) during the day (I have seen some).

Or failing that, an app?

Cheers, T i m

[Harry Bloomfield]

Tim Streater explained on 07/02/2018 :

There is enough polution up there!

[Huge]

The queue of people who would take that risk stretches out of sight round the block.

I think it's incredibly stupid.

[Richard]

They're all using the same movie set.

[Martin Brown]

Too bright for seeing any stars but Venus is doable from the ground when it is at its brightest and maximum elongation close to midday. You just need to stand out of direct sunlight and know exactly where to look.

The hard part is focussing your eyes at infinity.

I'd be very surprised if you couldn't see Venus from space. Or if a video camera didn't capture it in the same frame as a car if it was pointed in the right direction.

The albedo of Venus is 75% which makes it stand out nicely in sunlight.

[Martin]

Thunderbirds set for the return of two of the rockets. How do you explain the crowds who watched? Film extras provided by Rentacrowd

[Mark Allread]

[T i m]

;-)

Cheers, T i m

[Johnny B Good]

I'd have thought focussing your eyes to infinity would be easy seeing as how it's the result of relaxing the eye's focussing muscles used to accommodate for close in vision. Indeed, deep thought about a problem gives you that "Far Away Look", hence the word "consider" which literally translates as "to be with the stars".

That's almost twice as bright as Earth's albedo (39% back in 1976 when Vangelis released his space physics inspired concept album, "Albedo

0.39). Since Venus is closer to the sun, its brightness will be even higher than that simple albedo comparison suggests.

[Martin Brown]

The problem is that to see a faint white speck against a bright blue sky background you have to have an exact focus. Try it and see. It is also quite easy to lose the thing even after you find it the first time.

Looking at a nearby con trail and transferring your gaze to the right spot often works. Seeing a dot is much harder than you might think.

[nothanks]

Not quite correct. With nothing specific to focus on, the eye tends to settle at a couple of metres. All pilots are taught that lookout requires an active action of focussing on the horizon (and then breaking the scan into a series of segments where the eye is stationary, interspersed with re-focussing on the horizon). In the dark there's also the problem of the blind spot.

Many aero-med books discuss these but there are good articles here:

... snipped

[Steve]

It's a good job he's not in the UK as he'd have a hell of a job explaining to the DVLA why his car didn't need the VED paying.

Statutory Off Planet Notice?

[Adrian Brentnall]

I was wondering about that - "Exporting the car then are we Sir. Where to?"

[Johnny B Good]

All very interesting. I guess the real problem with 'focussing' on far away point sources of light is more to do with convergence than with focussing per se. In dim night sky viewing, you need the use of both eyes to mitigate the dark blind spot problem making use of both eyes correctly converged an important requirement.

Eye convergence on distant objects can't be guaranteed by relaxation alone, usually requiring some active trimming by muscular control. Generally, in a sort of learned "Pavlonian" styled response, the lens focussing muscle response takes its cue from the amount of convergence we consciously 'dial in'.

I know from my experience with atropine drops that, my eyes lose all accommodation powers leaving them relaxed into a state of focus at infinity so I'm pretty sure that that bit about the eyes being in an individually relaxed state when looking into the far distance is correct and the corresponding convergence whilst not trimmed to precisely fixate on a particular far and distant object when in deep thought, is sufficient to give the outside observer, of another in deep thought, the impression of "gazing at the stars" or the far away horizon.

However, when it comes to observing the "Morning" or "Evening" star, namely Venus, that generally doesn't present any great difficulty with naked eye observation since it is both very bright and discernible as a tiny crescent, unlike the dimensionless points of light we call stars.

I have to admit that 'focussing on distance objects' relies not so much on relaxed focussing muscles so much as on correct convergence which almost always is a matter of some active muscle control and less about total relaxation which usually only approximates the precise convergence required for viewing distant objects. As you pointed out, my throw away observation wasn't quite correct, merely just a small part of the whole story.

[nothanks]

Well, the correct name for the effect is "empty field myopia", which implies it is down to focus or, possibly, cognition. Muscles can only contract and when relaxed the ciliary muscle pulls the lens to its thinnest (longest focal length) condition ... so I can only surmise that either the ciliary muscle isn't fully relaxed in this state or there's summat else goin' on. I looked around for an explanation and stumbled over this google book, it doesn't have the answer but is a great thing to scan through:

[Martin Brown]

[snip]

For the avoidance of doubt I was talking about seeing Venus with the naked eye at or around midday in a clear blue sky with the sun well above the horizon. You need a good clear day and to stand in shadow.

The eye's default focus is as someone else has said is a few metres away from you if you have normal vision. You have to make an effort to bring the distant horizon into sharp focus assuming normal vision.

If you want a serious test of visual acuity try splitting the star epsilon-Lyra naked eye soon after dark it is a 3' arc double star - actually a double double in a small telescope it looks like:

.. :

with much bigger gap between then.