Astrarium

The aurora has been redrawn. • Colour is now computed from the emission lines themselves. Green (oxygen 557.7nm), red (oxygen 630.0nm), blue-violet (molecular nitrogen ion 427.8nm) and the crimson lower border (molecular nitrogen) are worked out from how strongly each one emits at each altitude, then converted to screen colour through the CIE colour matching functions. Red appears only high up because that line can only shine where collisions are rare, and the model now says so. • Curtains follow the magnetic field. Aurorae are lit by electrons coming down along field lines, so the curtain leans towards the equator as it rises and its rays converge on the magnetic zenith. Folds and vertical rays came with it. • Pulsating aurora. From midnight to dawn, patches tens to a hundred kilometres across blink with a period of a few seconds. Only the green pulsates. • High-altitude red aurora is now visible. The curtain is drawn to 600km and the path the line of sight takes through the emitting layer is counted, so the northern sky reddening as seen from lower latitudes now shows. • The jagged edge where the aurora met the horizon is fixed, and atmospheric extinction now carries it smoothly down to the horizon. • Auroral breakup. A new button plays out a substorm. The arc just before midnight (23h magnetic local time) brightens within seconds, swells 6 degrees (some 670km) poleward, and runs two and a half hours of magnetic local time westward — the westward travelling surge. The precipitation hardens, so the green deepens and the crimson lower border of molecular nitrogen appears. After a quarter of an hour the expansion phase gives way to some forty minutes of fading, through which the curtains turn into blinking patches. The clock runs at 60x while it plays and goes back to what it was doing afterwards. • The curtains are softer. The rays along the field lines stood out more sharply than they do in the sky; they are now blurred the way a real aurora looks. • Fixed the aurora breaking into gaps when zoomed in on the horizon view. • Forecasting the aurora now refreshes the space weather panel as well — solar wind events and the NASA/CCMC notices. The 3D solar system map has changed a great deal. • The paths 35 spacecraft actually flew are now carried inside the app (370,000 points), so Voyager's and Cassini's tracks are drawn where there is no signal. • Comets went from 951 to 4,122 — the MPC's file together with JPL's SBDB, which brings in the one-time visitors and the sungrazers. • Comets are now coloured by dynamical family: Jupiter-family, Halley-type, Encke-type, Saturn-family, and the Kreutz sungrazers (subgroups I and II). • Tap a body and its orbit is drawn, so you can see at a glance whether it belongs to the belt or to the outer system. • Two fingers pan the map; pinch zooms. The Sun no longer has to sit in the middle. • A new Data panel says where each table came from and when, and can fetch it again or go back to the one shipped with the app. • Bodies you search for and add now move along their orbits as the clock runs. The deep-sky star catalogue (2.34 million UCAC4 stars to 12th magnitude) is no longer carried in the app. Whoever wants it downloads it from the foot of the Explore tab, so everyone else is 37 MB lighter. Once downloaded it stays on the device and needs no connection afterwards. Also • Cards and panels can be picked up by the strip at the top and moved out of the way. • The Comets button now reaches to 18th magnitude, and only for a few objects, on nights when nothing is brighter than 12th. • AR works on the Mac as well, driven by hand where there is no orientation sensor. • Fixed a bug where the screen could keep shaking on iPhone. • Fixed a gap in the inner ring of the auroral oval when seen from inside the belt. • Fixed spacecraft on the 3D map not showing their description when tapped.