Recent Posts

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General Discussion / Re: Reports
« Last post by admin on September 01, 2020, 12:54:40 pm »
This report includes long-term light pollution studies using SQM meters from 2011:

Measurements of sky brightness at Bosscha Observatory, Indonesia by D. Herdiwijaya and others.
Connected meters (SQM-LE/LU/LR/DL) / Re: GPS integration
« Last post by admin on January 29, 2020, 10:09:31 pm »
Some computers reassign the communications port at power up or re-connection, so to ensure that the UDM can recognize both the SQM and the GPS, please follow these steps:
  • Disconnect the SQM and GPS from computer before powering up.
  • Power up the computer.
  • Start up UDM.
  • Connect the SQM and ensure you get a reading.
  • Disable the GPS connectivity from the log continuous tab.
  • Connect the GPS, and under the Log Continuous GPS tab ensure you are getting GPS location data.
  • Carry on from there.
General Discussion / SQMs strapped to a plane
« Last post by admin on December 31, 2019, 02:45:11 pm »
Here is an interesting report by Phil Langill using two SQM-LU meters strapped to the side of an airplane:

 Measuring and Monitoring Darkness at 10,000 feet (PDF)
 Measuring a darkness baseline for new developments near the Rothney Astrophysical Observatory
 Poster  presented at the Starlight Conference in Lake Tekapo NZ back in October 2019
 By Phil Langill – RAO Director, University of Calgary

General Discussion / [PAPER] Impact of Space Weather on the Natural Night Sky
« Last post by admin on November 06, 2019, 03:45:29 pm »
Here is an interesting paper on the Impact of Space Weather on the Natural Night Sky by Albert Grauer and colleagues using readings from the Unihedron SQM which will be presented at the IDA Annual General Meeting in Tucson Arizona on Saturday November 9 2019.

The abstract:
  In 2018, Solar Cycle 24 entered a deep solar minimum. During this period, we collected night sky brightness data at Cosmic Campground International Dark Sky Sanctuary (CCIDSS) in the USA (2018 September 4–2019 January 4) and at Aotea/Great Barrier Island International Dark Sky Sanctuary (AGBIIDSS) in New Zealand (2018 March 26–August 31. These sites have artificial-light-pollution-free natural night skies. The equipment employed are identical Unihedron SQM-LU-DL meters, used as single-channel differential photometers, to scan the sky as Earth rotates on its axis. We have developed new analysis techniques which select those data points which are uninfluenced by Sun, Moon, or clouds to follow brightness changes at selected points on the celestial sphere and to measure the brightness of the airglow above its quiescent level. The 2018 natural night sky was measured to −2change in brightness by approximately 0.9 mag arcsec at both locations. Preliminary results indicate the modulations of the light curves (brightness versus R.A.) we observed are related in complex ways to elements of space weather conditions in the near-Earth environment. In particular, episodes of increased night sky brightness are observed to be contemporaneous with geomagnetic activity, increases in mean solar wind speed, and some solar proton/electron fluence events. Charged particles in the solar wind take days to reach near-Earth environment after a coronal hole is observed to be facing in our direction. Use of this information could make it possible to predict increases in Earth’s natural night sky brightness several days in advance. What we have learned during this solar minimum leads us to search for other solar driven changes in night sky brightness as the Sun begins to move into solar maximum conditions.

You can read the paper here:

Connected meters (SQM-LE/LU/LR/DL) / Re: Observing Conditions interface in ASCOM 6.2
« Last post by admin on November 03, 2019, 01:53:27 pm »

Thanks to Martin Mangan at Dizzy Astronomy for updating his ASOM driver to 64 bit for Windows. You can get that here:

It allows operation of the connected SQM devices to N.I.N.A. software:
SQM-LU-DL (Datalogging light meter) / Erratic timing [SOLVED]
« Last post by admin on September 30, 2019, 10:54:10 am »
Symptom: Records are taken at irregular intervals even though the trigger was previously set at something like "every 5 minutes on the 1/12 hour".

Affected models: Anything shipped before 2019-09-30

Cause: The internal Real Time Clock lost power  (probably more than one week or longer)  and its wake-up alarm setting was not reloaded. Loading the alarm values is normally done by changing the logging mode.

If you do not want to install new firmware, just re-set the time in the meter, then switch the logging mode from OFF to the desired trigger which resets the wake-up alarm setting in the real Time Clock.

To plot this intermittent data without showing a broken line, select "Continuous line" from the settings section in the plotter. The broken line issue is caused because UDM guesses on where to separate different reading sessions with the break.

The proper long term solution is to upgrade the firmware which is very easy ...
Install the latest UDM (version number 239).
For Windows:
For MacOSX:
For Linux:

The new firmware is called:

The steps are:
  1 Connect the meter
  2 Start UDM
  3 Select the found DL meter
  4 Press Version button
  5 Go to Firmware tab
  6 Select SQM-LU-DL-4-6-73.hex
  7 Press Load Firmware button
  8 Wait until finished loading
  9 Select the found DL meter again
 10 Press Version button
 11 Proceed to set your Datalogger time and trigger as before.

This will not affect your existing records in the meter.
General Discussion / European Symposium for the Protection of the Night Sky 2019
« Last post by admin on June 21, 2019, 12:46:36 pm »
You may be interested in the "European Symposium for the Protection of the Night Sky":

November 3rd through 5th, 2019, in Mulranny, County Mayo, Ireland. The symposium will immediately follow the Mayo Dark Sky Festival:
Electromagnetic Radiation Spectrum poster / Updated 20" version of poster
« Last post by admin on May 14, 2019, 02:22:46 pm »
I have made some changes to the EMR poster so that it will ship at a lower cost (now 20" wide instead of 24" wide).

The latest version is close to being sent to the printer.

Here is a compressed thumbnail image:

You can see the full poster here (1.2MB PDF).

Github link here (spectrum20 branch.

You comments are welcome.
SQM-LU / Controlling SQM-LU with an Arduino/compatible
« Last post by admin on March 24, 2019, 10:59:24 pm »
Here is an example of connecting the SQM-LU (or SQM-LU-DL) to an Arduino compatible single board computer.

The Arduino compatible computer I used was the Teensy 3.2 which is availabke for about $19.80USD.

A USB host interface is required that the SQM-LU can be plugged into. I used the USB Host Shield V2.0 mini for about $4.85USD available from here:

The USB Host shield 2.0 is documented here:

The software library is located here:

Here is the schematic (PDF):

Here is the wiring diagram:

This is the code that I used:
Code: [Select]
#include <cdcftdi.h>
#include <usbhub.h>

#include "pgmstrings.h"

// Satisfy the IDE, which needs to see the include statment in the ino too.
#ifdef dobogusinclude
#include <spi4teensy3.h>
#include <SPI.h>

class FTDIAsync : public FTDIAsyncOper
    uint8_t OnInit(FTDI *pftdi);

uint8_t FTDIAsync::OnInit(FTDI *pftdi)
    uint8_t rcode = 0;

    rcode = pftdi->SetBaudRate(115200);

    if (rcode)
        ErrorMessage<uint8_t>(PSTR("SetBaudRate"), rcode);
        return rcode;
    rcode = pftdi->SetFlowControl(FTDI_SIO_DISABLE_FLOW_CTRL);

    if (rcode)
        ErrorMessage<uint8_t>(PSTR("SetFlowControl"), rcode);

    return rcode;

USB              Usb;
//USBHub         Hub(&Usb);
FTDIAsync        FtdiAsync;
FTDI             Ftdi(&Usb, &FtdiAsync);

void setup() {
  Serial.begin( 115200 );
  #if !defined(__MIPSEL__)
    while (!Serial); // Wait for serial port to connect - used on Leonardo, Teensy and other boards with built-in USB CDC serial connection

  Serial.println("USB Host starting up...");

  if (Usb.Init() == -1)
      Serial.println("OSC did not start.");
void loop()

    if( Usb.getUsbTaskState() == USB_STATE_RUNNING ) {
        uint8_t  rcode;
        char strbuf[] = "rx\r";
        rcode = Ftdi.SndData(strlen(strbuf), (uint8_t*)strbuf);
        if (rcode){
                  ErrorMessage<uint8_t>(PSTR("SndData"), rcode);
        delay(1000); //Wait a while for SQM to respond.
        uint8_t  buf[64];
        for (uint8_t i=0; i<64; i++)
            buf[i] = 0;
        uint16_t rcvd = 64;
        rcode = Ftdi.RcvData(&rcvd, buf);
              if (rcode && rcode != hrNAK)
            ErrorMessage<uint8_t>(PSTR("Ret"), rcode);
              if (rcvd > 2)

This is the output on the Arduino serial monitor:
Code: [Select]
USB Host starting up...
r, 09.37m,0000015912Hz,0000000000c,0000000.000s, 020.6C,D
r, 09.37m,0000015909Hz,0000000000c,0000000.000s, 020.6C,D
r, 09.37m,0000015909Hz,0000000000c,0000000.000s, 020.6C,D
r, 09.37m,0000015909Hz,0000000000c,0000000.000s, 020.6C,D

Some interesting troubleshooting notes are here:

General Discussion / Calibrating camera to produce SQM results
« Last post by admin on March 08, 2019, 01:28:18 am »
Here is a paper by Zoltán KOLLÁTH, and Anita DÖMÉNY  which provided detailed steps to calibrate an all sky image from a camera to produce mag/arcsec^2, similar to SQM meters:

An example image produced by Andrew Cool from Yadlamalka Australia
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