Orion/SLS "will eat NASA alive if they get there"

Chris Kraft in an interview:

The problem with the SLS is that it's so big that makes it very expensive. It's very expensive to design, it's very expensive to develop. When they actually begin to develop it, the budget is going to go haywire. They're going to have all kinds of technical and development issues crop up, which will drive the development costs up. Then there are the operating costs of that beast, which will eat NASA alive if they get there. They're not going to be able to fly it more than once a year, if that, because they don't have the budget to do it. So what you've got is a beast of a rocket, that would give you all of this capability, which you can't build because you don't have the money to build it in the first place, and you can't operate it if you had it.

The Search For Dark Matter – After The LUX Results

If you want to get "popular science" type of information about the current state in the search for dark matter (but without any of uniformed journalistic hyperbole sadly found in most of the press), then I can highly recommend this article by Matt Strassler. If you want slightly more scientific information, then this article by "Jester" is for you.

(Both articles via Sean Carroll.)

Make Your Own Mirror Blanks

Many people who get into ATM also grind and polish their own mirrors – but very few do make their mirror blanks themselves. Mike Davis uses a small kiln to cast his own mirror blanks from plate glass. He even does hexagon mirrors!

What I haven't seen yet is people doing coatings, be it for lenses, be it for dielectric filters – but you never know what amazing things people out there do in their garage.

Mel Bartels On Exit Pupil And Surface Brightness

Mel Bartels On Exit Pupil And Surface Brightness:

…
For extended objects, things are not as simple as stars. For starters, it is not possible to increase the surface brightness of an extended object by increasing the aperture. An example: take an object of 10 magnitude/ square arcsecond as seen by the unaided eye at night, exit pupil open to 7mm. Now, look at the object through a 10" scope. If there is no magnification to the image, the surface brightness will increase by the ratio of the scope's aperture to the eye's aperture squared, or, (10"/0.3")^2 =~ 1000x. However, in order to fit all of the light from the 10" aperture into the eye's exit pupil, we must use at least 33x. 33x will dilute the image brightness by 33^2 =~ 1000x, so we are back where we started. In fact, because of mirror coatings not reflecting 100%, and the small obstruction caused by a diagonal, the image brightness per area will actually be a little less than with the unaided-eye.

This leads to the interesting conclusion that the brightness of the sky glow as seen in the eyepiece is entirely dependent on exit pupil. At a given location on a given night, no matter the size of scopes, if they are giving the same exit pupil, then the sky glow brightness will be very similar.

So why then is aperture the dominant factor? If exit pupil or sky background brightness is kept constant, then as aperture increases so must the magnification. The object appears larger and is easier to see. It’s like moving in closer. If magnification is kept constant then the object and background brightness increase, also making the object easier to see.
…

This lead me to the interesting (and false!) conclusion that the brightness of any extended object is entirely dependent on the exit pupil – not quite so:

… Nils shows that the best contrast comes when the background is dimmed below visual detection and the object is about one degree in apparent size.

Mel Bartels On Limiting Magnitude

Mel Bartels has some thoughts on limiting magnitude (emphasis mine):

…Illumination drop-off at the edge of the eyepiece? Stated in percentages (e.g. 15% sounds terrible), should be in magnitudes (e.g. 0.06 mag, unnoticeable visually). Mirror coating reflections? Stated in percentages (e.g. 92%) should be in magnitudes (e.g. 0.04 mag loss). It is very difficult to see differences of 0.2 magnitude or less. And when the view is dimmed, both object and background are equally dimmed, leaving the contrast unchanged. Unless the view is grossly dimmed, the unchanging contrast means that the object does not lose visibility.
…

• Aperture is the biggest factor [duh!]. More aperture increases visibility regardless of magnification or power.

• Seeing the object in a larger scope then returning immediately to your smaller scope can result in a half magnitude gain.

• Observer experience is worth 2 magnitudes (I have a series of sketches of M31 from childhood onward).

• Observer variation is a half magnitude or more.

• Age matters a magnitude: young kids can see very faint stars; as we get older, our lens yellows and ability to detect fades.

• Knowing where to look and what to look for worth a magnitude.

• Averted vision is worth a magnitude.

• Dark adaption continues to produce increasing benefits for hours, ultimately worth maybe a half a magnitude.

• Field baffling is an overwhelming factor: the difference between nonexistent and fully baffled views can be worth magnitudes.

• Covering your head with a black cloth also yields improvements, perhaps on the order of a fraction of a magnitude.

• Time at the eyepiece is worth a magnitude (objects gradually become recognizable or detectable over a period of time, and then they fade after a prolonged period of continuous observing).

• Comfort at the eyepiece is worth a half magnitude.

• Rested eyes are worth half a magnitude. I often take short breaks throughout the night. Upon returning to the eyepiece I can see more until my eyes tire.

• Sky transparency is such an overwhelming factor; on rare perfect nights I’ve seen scopes perform as if they had almost unlimited aperture; let’s call superb sky transparency worth a magnitude or two.

• Filters are worth a magnitude.

• Visibility appears to correlate most with aperture, then apparent size (the greater the aperture, the greater the apparent size, limited by the full field of view).

• True binocular or two eyed viewing results in a half magnitude gain in stellar limiting magnitude and about a magnitude gain for extended objects.

Make these factors work for you and you can gain magnitudes in observing prowess. It’s like having a much larger scope on hand.