Sky Safari Plus/Pro now supports NEOs like 2012 DA14

[mithrandir (Andrew)]

Wonder if I can beat Tim/Bill to the punch.

Released today. There is a warning for Android. If on starting the second or third time after upgrading it downloads the data again, leave it at least 10 minutes before starting it again. This appears to be a Google problem.

Originally Posted by Tim on Y!

It's time to spill the beans. Apple has just released SkySafari Plus/Pro 3.7.3 for iOS, and we've released SkySafari 1.7.3 for Mac OS X and Android.

About 2 weeks ago, we started to get these questions about 2012 DA14, and why our apps fail to predict its position accurately. The problem was that SkySafari - like basically all other mobile and desktop planetarium apps - models the motion of comets and asteroids as having a simple Keplerian, elliptical orbit around the Sun. We did not take pertubrations by Earth's gravity into account. So any orbit that describes the asteroid's motion before the flyby will completely fail to predict its position afterwards, and vide-versa. After answering this question the 327th time, I finally decided to do something better.

The solution was to build an "orbit integrator" into SkySafari. Instead of modelling the trajectory of the asteroid as a simple Keplerian ellipse, we now model it using true N-body newtonian physics, taking the gravitational perturbations of Earth (and the Moon, Venus, Mars, Jupiter, and Saturn) into account, along with a decent numerical method (4th order Runge-Kutta). It took a few tries to get this right. After reaching out to some professionals in the field of solar system dynamics, we got some assistance JPL as well. JPL has made clear that they cannot officially endorse any commercial product, but I can confidently say they were impressed that we got this working on a smartphone at all.

We did take some shortcuts. Our model does not take relativity into account, nor the oblateness of the Earth. We also don't include Mercury, Uranus, or Neptune in the set of asteroid-perturbing masses. (Smartphones, whiie very capable, are still not supercomputers. The code still has to run fast enough to be useable.) Nevertheless, even with these shortcuts, our model predicts the position of 2012 DA14 to within arcseconds of JPL's positions on the day of the flyby and for many days before and after. We've even run our integrator out 9 years into the past or future, for a selection of different asteroids and comets, and in nearly all cases it does much better than a simple Keplerian orbit. So we're very confident that we're doing the math right.

Anyhow, that's the theory. In practice, here's what you need to know.

1) Plus and Pro only. The integrator is not in the Basic version.

2) You still need to update your minor body orbit data, just like you did before. The orbit integrator is useless if it doesn't have a decent orbit to start from.

3) The integrator only gets "turned on" when you select a particular comet or asteroid, and it's only used for the asteroid/comet you selected.

4) We run the integrator for one year in the past and future from the date of the orbital elements, using a 1-hour timestep. All that math takes about 1.5 seconds on my iPhone 4, which is the slowest device I own. (You'll feel a brief pause when first selecting a new asteroid or comet).

5) Since we only run the integrator one year from the date of issue of the orbital elements, don't try to use it to find out if asteroid Apophis will hit Earth in 2036. It won't work. At least not in this release. Yet.

So that's it for now. Have fun with it, and let us know how it works for you.

-Tim

[chrisp9au (Chris)]

Mmmm, tried updating SS+ on my Nexus 7 and am getting the repeated download problem.
I'll give it an hour and see what happens...

Cheers

Chris

[mithrandir (Andrew)]

Originally Posted by chrisp9au

Mmmm, tried updating SS+ on my Nexus 7 and am getting the repeated download problem.
I'll give it an hour and see what happens...

Since it appears to be still happening, here's are a couple of postings from Tim and Bill about the download issue:

I swear to you, we tried this multiple times on multiple devices and this never happened over here.

Best thing I can suggest is to delete the app from your phone and do a clean reinstall.

which was reported to fix it and did preserve settings, and

We are still unable to reproduce these Android problems over here. We have done repeated reinstalls, etc. under the debugger and everything works perfectly.

The log files you have sent indicate the Google Play is sending your app the wrong version of the data (v1.7.0, not v1.7.3). But everything looks fine in our Google Developer account - the apps are set up correctly, with the right data assigned to each.

Perhaps Google's servers have not propogated the change correctly all around the world. We suspect this is a temporary Google glitch that may just go away in the next 24 hours or so, on its own.

and

We are still not sure why this is happening, but we suspect it will fix itself if you wait at least 10 minutes before trying to run again. After that the problem should not reoccur. Yes, I know it sounds strange, but sometimes Google doesn't provide us with a valid data file name unless you wait a bit between runs. If you had this problem and later it went away, please email us to let us know that that fixed it.

So far this hadn't worked for those who had tried it.

[chrisp9au (Chris)]

Success!

Re-installed SS+ (1.7.3) and updated minor planet data, all appears to be working just fine!

Thanks Andrew, Tim, Bill

Chris

[netwolf]

Mine keept looping through the download and install of new data post update. After data download and install, when you try minor planets update it says you need to complete download and install of data. So exit and open again and again the download and install happens. Just keeps looping. So uninstalled and reinstalling now, hopefully will resolve.

[netwolf]

Reinstall has fixed it. I can now locate DA14 excellent. Thx

[mithrandir (Andrew)]

Latest on the Android version from Southern Stars.

First, if your device now seems to redraw slowly:

Originally Posted by Tim

I can reproduce this [slow redraw] problem, to some extent, on my Samsung Galaxy Tab 7.0. It's not as bad for me as for you, but then we have different devices. First good news: it's not a bug, and there is an easy fix.

First the fix: go to Settings -> Solar System and change the limiting magnitude for solar system objects to something reasonable, like 15 or 18. (I mean, you can't see things fainter than that anyhow.)

The full story:

Here's what's happening. In SkySafari versions before 1.7.3, we internally treated all solar system objects with magnitudes > 20 as infinitely faint. Now, we don't - we actually try to draw everything up to the Solar System magnitude limit. And there are a ton of those faint little asteroids. So your Android is trying to draw a lot more faint asteroids than before. And it just can't keep up.

I do not see the same slowdown on any of my iOS devices. The same issue is there, but the graphics processors, and the iOS graphics pipeline, is just hands-down much faster than on comparrable Android devices.. This is simply a known a limitation of Android. You just have to draw fewer asteroids for it to keep up.

Second, if you've got 1.7.3 working properly you don't need this one.

Originally Posted by Bill

We think we understand the problem and will spin a 1.7.4 release later today. We really don't need any more chatter on the list telling us if it worked or didn't.

It seems to only affect certain versions of Android or certain versions of the Google Play app, we can't tell exactly which. It never happens on any of our devices so we didn't see it.

Have we mentioned lately how frustrating Android can be to program for? It is just not set up to handle the large databases we need.

Before the release, you can fix it by either:

1. Going to the Android Settings app, doing a "Force stop" and then a "Clear data" on SkySafari (you will be asked to download the data when you rerun).
2. Delete and re-install the app.

In either case your settings and observing lists will be preserved.

[dannat (Daniel)]

Can someone with the android pro or plus version tellme in the settings date/time section if the local sidereal time is displayed?

[Forgey (Paula)]

Originally Posted by dannat

Can someone with the android pro or plus version tellme in the settings date/time section if the local sidereal time is displayed?

I have the Pro version and it is displayed on mine.

[chrisp9au (Chris)]

Originally Posted by dannat

Can someone with the android pro or plus version tellme in the settings date/time section if the local sidereal time is displayed?

I have the Plus version, Local Sidereal Time is displayed.

Cheers

Chris

[dannat (Daniel)]

Thanks Paula & Chris