Lunar Crescent Workshop (Thierry Legault)

Lunar Crescent Workshop

Thierry Legault

Surabaya, Indonesia

April 26-28 2014

Edition 2

Lunar crescent workshop - Thierry Legault 2014 1

Agenda: day 1

• The Moon and the crescent:

– Basic notions

– Using Stellarium planetarium program

– The lunar phases

– Seeing and imaging the crescent

• The GM8 mount and the Gemini2 system:

– assembly and installation

– polar alignment

• Outdoor practice with GM8 and Gemini2


Agenda: day 2

• Imaging:

– Setting the telescope

– Making and using the solar filter and the sunshield

– Adjusting the solar and lunar rates

– Pointing the Sun and the Moon

– Checking the celestial coordinates

– Using the video camera

– Processing the video sequences

• Outdoor practice with GM8 (optional)


Agenda: day 3

• Outdoor practice of lunar video acquisition

• Processing the video sequences

• Workshop feedback/wrap-up


Basic notions:

angles in astronomy


• An angle represents the apparent size of an object or the apparent distance

between two objects

• Moon = Sun = ½° diameter

• The angle between the Moon and the Sun is called the Elongation

Basic notions:

the Universal Time (UTC)


• UTC = Universal Time Coordinated

• Reference for astronomical and scientific/technical world

• Formerly: Greenwich Mean Time (GMT)

• West Indonesia = UTC + 7h

• Central Indonesia = UTC + 8h

• East Indonesia = UTC + 9h

The Moon and the crescent:

using Stellarium


Startup


using Stellarium


Choosing location


using Stellarium


Choosing location


using Stellarium


Choosing date/time


using Stellarium


Choosing date/time


using Stellarium


Choosing speed


using Stellarium


Finding object


using Stellarium


Finding object


the lunar phases


(source: http://upload.wikimedia.org/wikipedia/commons/4/46/Moon_phases_en.jpg)


the lunar phases


• The phase is the fraction of the lunar disk illuminated by the Sun as seen from

Earth:

• Full Moon (all night) = 100%

• First/Last Quarter (evening/morning) = 50%

• Visible Crescent (sunrise/sunset) = a few percent

• New Moon (daytime) = less than 1%

• Total solar eclipse = 0%

• Average time between two Full Moon or two New Moon: 29d 12h 44m 2.9s

• New Moon can happen at any hour (day or night), depending on the date


the lunar orbit


Inclination of lunar orbit ~ 5°

with respect to ecliptic (Earth orbit plane)


the conjunction


• Conjunction (New Moon) happens when:

lunar ecliptic longitude = solar ecliptic longitude

• Topocentric conjunction: as seen from a specific place on Earth

• Geocentric conjunction: as seen from the center of the Earth

• Topocentric and geocentric times may differ by up to 4 hours, because of the

parallax

• At conjunction, the Elongation (EL) can take any value between -5° and +5°

• When EL is less than ½°, there is a solar eclipse (partial or total)

• The Age of the Moon is the time passed after conjunction

• The EL increases with the Age, at an average of 12°/day

• Crescent brightness and thickness increase with EL

• Solar glare decrease with EL


the elongation in Stellarium



visibility of the first thin crescent


Conjunction Later


visibility of the first thin crescent


• Visibility with naked eye or binoculars needs:

• a dark sky => after sunset

• the Moon a few degrees above the horizon

• This implies a lower limit to EL => 12 hours minimum after conjunction

• Moonset (Moon at horizon) is invisible because of atmospheric extinction

(absorption of light)

• Transparency of the atmosphere is very important:

• no clouds

• no fog, smoke, pollution, humidity => blue sky even close to horizon

• moutain sites are often better (if no high clouds)


the conjunction crescent (1/2)


• EL is always less than 5°

• The Moon and the Sun set almost at the same moment

• The conjunction crescent is detectable in daylight only with photography

• Visibility with the eye (naked or aided with telescope) is physically impossible

• Daylight photography needs infrared filter (and monochrome sensor, sensitive to

infreared) to decrease the brightness of the blue sky


the conjunction crescent (2/2)


• The EL must not be too small

• World record so far: EL = 4.2°

• Transparency of the atmosphere is critical:

• no clouds

• no fog, smoke, pollution, humidity => blue sky even close to the horizon

• moutain sites are often better (if no high clouds)


topocentric conjunction time


Find the time when Ecliptic Topocentric longitude of Moon and Sun are closest














visibility charts


http://www.icoproject.org/

http://www.staff.science.uu.nl/~gent0113/islam/islam_lunvis.htm

Charts are approximations based on past experience and lunar position calculations






visibility charts



visibility charts



visibility charts



visibility charts


The GM8 mount:

assembly and installation


Deploy the tripod legs

The GM8 mount:



Extend the tripod legs

Do not install the tripod

on loose or unstable

ground where the tripod

can sink or slide

(sand, mud, gravel…)

The GM8 mount:



Install the mount on the tripod and tighten the 3 screws

The GM8 mount:

the axis of the mount


Movement axis:

- RA = Right Ascension

- DEC = Declination (δ)

Polar alignment axis:

- AZ = Azimuth

- LAT = Latitude

The GM8 mount:

the equatorial coordinates


RA is expressed in hour/min/sec

05h 34m 56s

Range: 0 to 23h 59m 59s

DEC is expressed in degrees/min/sec

45° 12’ 09’’

Range : -90° to +90°

The GM8 mount:



Direct the polar axis leg to South for the southern hemisphere (North for northern hem.)

with the help of the compass

The GM8 mount:



Adjust the tripod legs for horizontality (2 bubble levels)

Bad Good

The GM8 mount:



Pre-adjust the latitude of the observation site with the LAT knob and scale

The GM8 mount:



Use a bubble level and a triangle (cut according to the latitude) to adjust the latitude.

If necessary, use the polar axis leg extension

The GM8 mount:



The latitude triangle

Surabaya example: latitude = 7.25°; tan(7.25°) = 0.127; 200*0.127 = 25.4 mm

The GM8 mount:



Screw the counterweight bar and install the counterweight

The GM8 mount:



Install the telescope (« CWD » position = CounterWeight Down)

The telescope:

components


The GM8 mount:



Unscrew RA knob, adjust counterweight balance.

Check that the counterweight does not touch the tripod leg.

Put the mount in « CWD » position. Screw RA and DEC knobs.

The GM8 mount:



Install the control panel.

The GM8 mount:



Screw the RA motor.

Plug the RA cord between the control panel and the RA motor

The GM8 mount:



Screw the DEC motor.

Plug the DEC cord between the control panel and the DEC motor

The GM8 mount:



Plug the hand controller in « Graphic HC ».

The GM8 mount:



Plug the GPS in « Serial port 1 »

The GM8 mount:



Plug the 12V power supply

The GM8 mount:

The Gemini 2 system


Complete user manual:

http://www.gemini-2.com/




The Gemini 2:

initialization


Switch on the mount while in « CWD » position

Let the star display pass

The Gemini 2:

initialization


Press « cold start », « Back »

The Gemini 2:

initialization


Press « Back » again to go to the Main Menu page

The Gemini 2:

site check


From Main Menu page, press « Menu », « Site »

Press « Query GPS » when outside and check coordinates and Timezone

The Gemini 2:

time check


From Main Menu page, press « Menu », « Time »

Check (or change) Timezone, Civil date and Civil Time, press « Set »

The Gemini 2:

mount parking


From Main Menu page, press « Menu », « Park », « Park at CWD Position »

The GM8 mount:



Align the finder on a distant target (terrestrial at several km, or celestial)

The GM8 mount:

polar alignment (southern hemi.)


• Polar alignment consists in physically aligning the polar axis of the mount with the

polar axis of the Earth, so that:

• all stars can be perfectly tracked with the rotation of the RA axis of the mount

at sidereal rate (one turn in 23h 56m 4.09s)

• The « GOTO » system of the mount can point any celestial object with

sufficient accuracy

• Poor polar alignment leads to a drift of objects in the field of view (eyepiece or

camera)

• For crescent imaging, polar alignment shall be better than 3 arc minutes (1/20 °)

The GM8 mount:

setting the sidereal tracking rate


From Main Menu page, press « Menu », « Track », « Sidereal »

The GM8 mount:

polar alignment southern hemi.


Point a bright star at North and altitude between 30° and 60° (halfway between

horizon and zenith).

The GM8 mount:



Align the axis of the crosshair eyepiece with the axis of the mount

The GM8 mount:



If the star drifts up, use the AZ knob to rotate the mount counterclockwise

If the star drifts down, use the AZ knob to rotate the mount clockwise

Repeat the corrections until there is no visible drift during at least 3 minutes

The GM8 mount:



If the star drifts up, use the AZ knob to rotate the mount counterclockwise

If the star drifts down, use the AZ knob to rotate the mount clockwise


The GM8 mount:



Point a bright star at East and low altitude (15 to 25°)

The GM8 mount:



If the star drifts left, use the Latitude knob to pull down the polar axis

If the star drifts right, use the Latitude knob to pull up the polar axis

Repeat the correction until there is no visible drift during at least 3 minutes

The GM8 mount:



If the star drifts left, use the Latitude knob to pull down the polar axis

If the star drifts right, use the Latitude knob to pull up the polar axis


The GM8 mount:



Go back to the previous star and check the drift, etc.

Make adjustments until there is no visible drift on both stars during at least 3 min

The GM8 mount:

polar alignment northern hemi.


Point a bright star at South and altitude between 30° and 60° (halfway between

horizon and zenith).

The GM8 mount:



Align the axis of the crosshair eyepiece with the axis of the mount

The GM8 mount:



If the star drifts up, use the AZ knob to rotate the mount clockwise

If the star drifts down, use the AZ knob to rotate the mount counterclockwise


The GM8 mount:



If the star drifts up, use the AZ knob to rotate the mount clockwise

If the star drifts down, use the AZ knob to rotate the mount counterclockwise


The GM8 mount:



Point a bright star at East and low altitude (15 to 25°)

The GM8 mount:



If the star drifts left, use the Latitude knob to pull up the polar axis

If the star drifts right, use the Latitude knob to pull down the polar axis


The GM8 mount:



If the star drifts left, use the Latitude knob to pull up the polar axis

If the star drifts right, use the Latitude knob to pull down the polar axis


The GM8 mount:



Go back to the previous star and check the drift, etc.

Make adjustments until there is no visible drift on both stars during at least 3 min

The GM8 mount:

polar alignment


CAUTION:

If the mount or one leg of the tripod is moved,

even by 1 mm,

Alignment is LOST

Imaging:

setting the telescope


Imaging:

making the solar filter


Use the instruction sheet provided with the filter:

http://www.baader-planetarium.com/sofifolie/bauanleitung_e.htm

Internal diameter of housing matches the external diameter of the end of telescope




Imaging:

making the sun shield


Use currugated cardboard roll, width at least 1.20 m

Imaging:

making the sun shield


Cut cardboard at least 1.20m long, make a tube, insert it over the telescope shield

and fix the ends with cord

Imaging:

pointing the Sun


From Main Menu page, press « GOTO », « Solar system », « Sun »

Imaging:

setting the solar tracking rate


From Main Menu page, press « Menu », « Track », « Solar »

Imaging:

synchronizing on the Sun


From Main Menu page, press « Menu », « Align », « Synchronize »

The display comes back to Main Menu page saying: Sync Sun

Imaging:

pointing the Moon


From Main Menu page, press « GOTO », « Solar system », « Moon »

Imaging:

calculating the lunar tracking rate (1/3)


Note the RA/DE (of date) lunar coordinates in Stellarium, 1 hour before

and 1 hour after the imaging time (here: 2:46:25)

Imaging:



Input them in the lunar rate calculation Excel sheet

Imaging:



Press Menu, Track, User Define.

Input the calculated differences Delta RA and Delta DEC in the User

Define Rate page of Gemini2, with timespan = 2:00:00, then press « Set »

Recalculate every 1 hour or so

Imaging:

setting the lunar tracking rate


From Main Menu page, press « Menu », « Track », « Comet/User Defined »

Do NOT use « Lunar »

Imaging:

checking the lunar/solar coordinates


Compare Main Menu RA/DEC coordinates to RA/DE (of date) in Stellarium

Difference must be less than 1m / 15’

Imaging:

video acquisition


Pulg the camera to the computer and launch iCap software

Imaging:

video acquisition


View useful toolbars

Imaging:

video acquisition


View histogram

Imaging:

video acquisition


Choose record directory and video filename with time stamp

Imaging:

video acquisition


Choose frame rate as maximum possible (30)

Imaging:

video acquisition


Choose format AVI and Codec RGB24 (uncompressed)

Imaging:

video acquisition


Choose video sequence duration: click on Toggle Recording Control Dialog,

then on the little clock and input duration

Imaging:

video acquisition


Let gain at 0.00 dB, manual (no Auto)

Imaging:

video acquisition


Adjust exposure time so that histogram maximum is 2/3 to 3/4 of the range

Imaging:

video acquisition


Bad: underexposed Bad: overexposed

Imaging:

video acquisition


Launch video sequence acquisition with « start recording » button

Imaging:

video acquisition


View elapsed time and number of frames with Record Video File dialog box

Video processing step 1


Launch VirtualDub and open the AVI video file to process



Export to a BMP image sequence

Name: i

Minimum number of digits: 1



Export to a BMP image sequence and note the number of last frame (here 887),

Click OK and let the process finish (a few minutes needed)



Launch Iris and check the presence of the Command window

and the Threshold window

Video processing


Settings of Iris (to do once): set the working path = video directory

and file type = FIT



Convertion: in the command window, type convertbmp24 i i N

Press enter and let the process finish (a few minutes needed)

(N is the number of the last bmp file)



Stacking: in the command window, type add_norm i N

Press enter and let the process finish (a few minutes needed)



Background removal: click Processing, Wavelet



Background removal: slide Remain to 0 (left) and press OK



Background removal: in the Command window, type offset 16000

Press Enter

Slide the high threshold to the right (32767)



Slide little by little the high threshold to the left and the low threshold to the right

to increase contrast



Save the image in JPEG: click File then Save

Choose JPEG as file type and give a name

Imaging checklist


1. If necessary, switch on the mount (CWD position)

2. Install the solar filter

3. Point the Sun with GOTO

4. Focus the Sun through the eyepiece

5. Connect the video camera to the computer and launch iCap software

6. Adjust video camera parameters for good visibility of sunspots

7. Focus carefully on sunspots through the video image

8. Center the Sun in the camera frame with the hand controller buttons

9. « Synchronize » the Gemini2 on the Sun

10. check solar RA/DEC coordinates

11. Point the Moon with GOTO and check RA/DEC coordinates

12. Remove the solar filter

13. Calculate and set the lunar tracking rate

14. Adjust video camera parameters for lunar acquisition

15. Take video sequences of 1 minute long

16. Every hour or so, check focus and re-synchronize on the Sun (step 2 and more)

Possible mistakes and problems


Problem Symptom

Poor polar alignment Objects drift in sensor/eyepiece

Wrong tracking rate Objects drift in sensor/eyepiece

Wrong time or site Wrong direction when use of GOTO

Poor focus Objects fuzzy (or not visible) in

sensor/eyepiece

Solar filter not in place for Sun Danger for sensor or your eyes!!!!!!!!!!!!!!!!!!!!!!!

Solar filter in place for Moon Nothing visible (black image)

Mount axis not tighten Wrong direction when use of GOTO

Mount axis moved manually after

polar alignment/synchro

Wrong direction when use of GOTO

Tripod moved or az/lat knobs touched

after polar alignment

Polar alignment lost

Message « motor stalled » Motor disconnected

The 3 keys for success


Train

Train

Train



Notes


Notes


Notes


Notes

Documents

Lunar Crescent Workshop (Thierry Legault)