Aurora Forecast 3D
     - Satellite

Release v4.5

Quick look guide

Thanks for installing the Aurora Forecast 3D - Satellite. Hopefully, you will enjoy it and make use of it as a tool to track down the aurora. It renders the Earth in 3D with rotation and scaling at your fingertips. You can mark location and make your own Station anywhere on the planet. The Sun illuminates the globe as it updates in near real-time (1s). The short term forecasts are up to +6 hours, while long term forecast are up to 3 days ahead in time. They are updated when the app is active and connected to internet.

The Skyview module shows a fish-eye view of the sky including the auroral ovals, satellites, planets and stars as seen from any ground point location.

Below is a short description on how to use the app.

Legend

The above screen shot is marked with text labels. The circular green/red transparent belt is the aurora oval [1,2]. The red colored part of the oval represent the dayside Cusp aurora. Two colored polygons mark the positions of your Station (red) and the Ground-track point (orange). The optical horizon for 110 km of altitude is visualized as a transparent disk centered at the track point.

City lights are included based on data from the NASA/Goddard Space Flight Center[3]. In addition, an aurora compass is shown in the top left corner and 8 x speed buttons are grouped to the right. The auroral activity is presented using a speedometer layout.

The Aurora Compass

The Aurora Compass shows where the auroral oval is located as you look up at the sky from the center Ground-track point.
This point is marked with an orange circular polygon on the Globe. Tap it, if you want to mark it as "Marked location". The latitude and longitude are shown at the top of the screen. You can rotate the Globe to move to any desired position.

The oval all-sky cover is shown in percentage in the center of the compass. The orange star marks the position of the Sun in the compass. The Moon symbol is explaned below according to phase and age. These will only appear if they are within the field of view as seen from the Ground-track point.

The Moon

The above symbols represent the Moon as observed from the northern hemisphere. In the southern hemisphere these moon symbols are swapped horizontally (mirrored).

Kp index indicator

The speedometer is used to visualize the auroral activity based on the Kp index (0 - 9).
The index is a measure on how disturbed the planetary geomagnetic field is. It is directly related to auroral activity. The short term predicted Kp values (0, +3 or +6 hours) are estimated by the Space Weather Prediction Centre (NOAA-SWPC) using satellites that monitor the Sun.

Hint: You can set your own Kp index by tapping the color scale on the wheel.

Buttons

Aurora sky view probability as seen from the Ground-track point.
+0 hour Nowcast.
+3 hour Forecast.
+6 hours Forecast.
Toggle Day/Night ON/OFF.
Return to Station point.
Zoom RESET.
Zoom IN.
Zoom OUT.
Share Screenshot (Android and iOS)
Repeat news ticker - text line
Track Satellite position

The Sun

The Planets

The positions [4] and apparent size of the inner planets are scaled in 3D according to the size of the Earth, but the distance is for artistic reasons not correct. It is in reality much further away. The apparent distance of the Sun is scaled down 500 times. The outer planets are scaled down and located at infinity close to the stars. Textures of the Earth, the Sun and the Moon are downloaded from the internet [5,6].

The Stars

The stars in the 3D viewport are from the Tycho catalog sky map by NASA [7] version 2.0. The map is projected using a cylindrical-equidistant transform that is wrapped to a outer celestrial sphere.
The red cross in the star map marks the position of Zero Right Ascension (RA) and Declination (DEC).
It is known as the First Point of Aries and is the location of the vernal equinox

The Satellites

The positions of the satellites are calculated by code [8] based on Two-Line Element (TLE) sets provided by the Center for Space Standards and Innovation (CSSi). Each set groups the satellites according to mission objectives like communication, navigation or pure scientific purpose etc. The TLE sets are updated automatically every 72 hours. You may force an updated TLE by using the "Refresh" button in the "Edit" menu.

Default satellite is the International Space Station (ISS). Hit the "Track" button in the "Setup" menu to locate the current position of it.

The Skyview module

The Skyview module is activated by tapping the Aurora Compass in the 3D viewport. The Bright Star Catalogue edition 5 (BSC5) [9] is used to plot stars brighter than magnitude 4. A red circle identifies the selected object to track in azimuth (AZ) and elevation (EL).

The ForeCaST (FCST) module

The FCST (ForeCaST) module summarizes the 3-day forecast from NOAA-SWPC. Three hours wide color coded bars are plotted as a function of time. The storm limits at Kp = 5 and Kp = 9 are plotted as two red horizontal lines. The highlighted bars are the current short term forecasts, accompanied by a five line text summary. You may click on each bar to view the effect in both the 3D viewport and in the Skyview module.

Note that any aurora occurrence of the 3-day long term forecast depends highly on the solar wind IMF configuration, and might not kick in.

Make your own station list

You can make your own station or modify the pre-defined station list that came with the app. Note that it is not possible to delete "Marked location". It is hooked up to the on click handler of the Ground-track point. Go to the "Setup" menu and open the Editor by clicking on the "Edit" button.

STEP 1
First, enter only letters for the station name. All numbers are float using the dot "." as decimal separator. Latitude must be entered as decimal degrees and is positive to the North and negative to the South. Correspondingly, longitude is positive to the East and negative to the West. The altitude is in units of meters (m).

STEP 2
Secondly, test the input values by using the "Check" button. If this operation ends with an "OK", then proceed to the third and final step.

STEP 3
The station is added to the end of the list if you hit the "Add" button. It will be deleted from the list if you use the "Delete" button. If you simply want to modify or update the station, then use the "Update" button.

Hint: Zoom IN the 3D viewport and press (click) on the Ground-track point to update "Marked Location". Then change the name of it and simply add it as a new station.

STEP 4
Finally, save your new station list and default settings for the app by clicking the "Save" button in the "Setup" menu.

Alert messages

If a geomagnetic storm occurs (Kp>5), then you will receive an alert message. It pops up as a vertical aligned text line to the left in the 3D viewport. The alerts are grouped according to the definition provided by NOAA-SWPC.

Geomagnetic storms
Scale
Description
Kp
Frequency
G1
Minor
5
1700
G2
Moderate
6
600
G3
Strong
7
200
G4
Severe
8
100
G5
Extreme
9
4
The frequency is number of events per solar cycle (11 years).

Acronyms and abbreviations
Short
Description
AR
Active sunspot Region
AST
Apparent Solar Time
CH
Coronal Hole
CIR
Co-rotating Interaction Region
CME
Coronal Mass Ejection
DSF
Disappearing Solar Filament
FCST
ForeCaST
HSC
Heliospheric Current Sheet
HSS
High Speed Stream
IMF
Interplanetary Magnetic Field
L1
Lagrangian point 1
LHA
Local Hour Angle
SI
Sudden Impulse
SIR
Stream Interaction Region
SPE
Solar Proton Event
SSBC
Solar Sector Boundary Crossing
UT
Universal Time

In addition to the above forecasts, three day alerts from NOAA-SWPC are shown as sliding text - news ticker. Click bottom left button to repeat message. Enable the "Alerts" checkbox in the "Edit" menu to use this option (Default is ON).

Travel tip

First, locate a city or an airport above the Arctic Circle. Secondly, remember that it has to be dark. The Sun needs to be ~10 degrees below the horizon. Otherwise, the aurora will be drowned in solar light. In the northern hemisphere, this means late autumn to early spring with best viewing conditions during the late afternoon and into the night. At Svalbard we see it all day during mid-winter. Thirdly, I would recommend a location where there is stable in-land climate during the winter. For example, Fairbanks in Alaska or Alta in Norway are excellent locations. Another option is to take a boat trip and hunt for clear skies.

How to hunt for the aurora

For most people on Earth, you will have time to eat dinner. Then check your local weather forecast for clear skies. Start the app and locate the auroral oval. If you have a clear view of the oval above your head, seen in the Aurora Compass, then you have up to 75% chance to see the aurora. Happy hunting!

Change time

The app is setup to Nowcast and Forecast in Universal Time (UT). The Apparent Solar Time (AST) is calculated using the Local Hour Angle (LHA) of the Sun. As a consequence, AST depends on you location and may be crudely measured with a sundial.

If you want to change date to study the ovals at any other time epoch, then enter the 'Edit' menu. Enable the 'Prediction' checkbox and enter the date selection menu. Do the same for the 'Update' menu to set the clock. You can now also change the Kp index by tapping the color wheel in the Kp-indicator.

Network and settings

Note that the app will still work if your device is not connected to the internet. But the Kp index and the alerts are then not updated. The help file is locally installed and do not require a network connection. Default input values and locations can be restored. Close the app and delete the cash / data used by the app. This is done in your phone's settings. You can now restart with default settings.

Warning sign

A warning sign appears when the forecasts are not valid or when there is no internet.

References

[1] Sigernes F., M. Dyrland, P. Brekke, S. Chernouss, D.A. Lorentzen, K. Oksavik, and C.S. Deehr, Two methods to forecast auroral displays, Journal of Space Weather and Space Climate (SWSC), Vol. 1, No. 1, A03, DOI:10.1051/swsc/2011003, 2011.

[2] Starkov G. V., Mathematical model of the auroral boundaries, Geomagnetism and Aeronomy, 34 (3), 331-336, 1994.

[3] The Visible Earth catalog, http://visibleearth.nasa.gov, NASA/Goddard Space Flight Center, April-October, 2012.

[4] P. Schlyter, How to compute planetary positions, http://stjarnhimlen.se, Stockholm, Sweden, 1979.

[5] T. Patterson, Natural Earth III - Texture Maps, www.shadedrelief.com, October 1, 2016.

[6] Nexus - Planet Textures, www.solarsystemscope.com, January 4, 2013.

[7] Bridgman, T. and Wright, E., The Tycho Catalog Sky map- Version 2.0, NASA/Goddard Space Flight Center Scientific Visualization Studio, http://svs.gsfc.nasa.gov, January 26, 2009.

[8] Vallado, David A., Paul Crawford, Richard Hujsak, and T.S. Kelso, Revisiting Spacetrack Report #3, AIAA/AAS-2006-6753, https://celestrak.com, 2006.

[9] Hoffleit, D. and Warren, Jr., W.H., The Bright Star Catalog, 5th Revised Edition (Preliminary Version), Astronomical Data Center, NSSDC/ADC, 1991.

Copyright
The application is made by F. Sigernes (email: freds@unis.no), Longyearbyen, Svalbard, Norway (2016). It is considered licensed as fredware.