Author: Richie Jarvis © 2020-07-09

Website: https://deepsky.org.uk

Contact: richie@deepsky.org.uk

Description of Parts

The camera is a peltier cooled CCD chip with a black and white Sony HDR sensor.  Made by Starlight Xpress Instruments, the model is the SX814 Monochrome camera.   To reduce electrical noise, it is cooled to -30 degrees below zero using an electrical cooler. Professional observatories use liquid nitrogen to do the same job.

Before I can start taking exposures, some initial calibration of the equipment is required.  The computer needs to know where it is on Planet Earth as well as what time it is. GPS can be used is used to get that information, or it can be entered manually, using Google Maps, or the Internet to find the correct Latitude and Longitude.  Once entered, the computer stores this information for future reference.

Initial Setup

Starting with the telescope in the home position, pointing North and with the weights down.  Using the computer sky chart to control the mount to move the telescope to a bright star, and line it up on the camera chip.  Repeat that three times and the computer knows how reality relates to its internal model of the sky.  Luckily, if I “park” the mount after use, and don't knock it, it keeps pretty good alignment night after night, so I only need to repeat the full Initial Setup procedure once or twice a year.

Focusing the Camera

Before taking any exposures for use in an image, the telescope and camera need to be focused.  Focus changes with temperature, this also means that each night the focus position will be slightly different.  To add complexity, as the equipment cools, and contracts, the focus point changes.  The automatic focuser I use, a Starlight Instruments (no relation to the camera manufacturer) Focuser Boss II Electronic Focusing Control and stepper motor.  This unit learns the change in focus over a 5 degree celsius temperature drop, and using that calibration compensates for changes as the temperature drops automatically.

Before any of that, I need to find a star, and carry out an initial focus run.  This is complicated further as each filter has a slightly different focus point.  Each time I change the filters in the filter-wheel, I need to recalculate the relative differences in position between the Red, Green, Blue, Clear, Hydrogen Alpha, Oxygen 3, Sulphur 2 and Hydrogen Beta filters.  Each one has a slightly different focus point.  More calibration, but the relative calculations stored. I usually redo that once a year, or if I change the filters around.

Slewing to target

Once the stars are focused, I pick a target, say a galaxy or nebula, and tell the scope to slew (move) to point at that location.

The guide camera (CCD2) now needs to be told how it is aligned.  This is a simple software routine which involves the computer making small movements to figure out which way the motors move in relation to the stars.  Once done, it locks on and removes tracking errors automatically.

CCD1 is then ready to take a long exposure.  At this point, CCD2 is taking pictures every second, sending commands to the mount motors to correct for errors.  This keeps the stars on the same pixels on CCD1 during a long exposure!  Otherwise you get lines, not points of light, and those do happen but go in the bin.

I take many exposures because the objects are so very very dim that long exposures to collect as much light as possible for a long time.  That also introduces random noise in the raw data.  To remove that, astrophotographers take multiple exposures for each filter. Some images require all the filters.

Example Results - Messier 51 - The Whirlpool Galaxy

Here is some more of my processed and published work:

https://deepsky.org.uk/astro-imaging.html

All images and text are licenced under the http://creativecommons.org/licenses/by-nc-sa/2.0/uk/

Contact: Richie Jarvis richie@deepsky.org.uk

© 2020-07-09

Here is the result:

Full capture details & clickable large image available here

I have had some nice activity on it which looks good at 120fps

(note to self... Upgrade Joomla and get youtube support...)

Linky here:

https://youtu.be/EqNL-PYjchI

I've been playing for the last few nights with anything vaguely clear (its been shocking!).  Tonight I finally had a decent sky to play with for a little while, so went back to my old favourite Messier 51, the Whirlpool Galaxy (here for info and some of my other shots).  Mounted as usual on my EQ6 Pro and through the F/7 TMB 115mm running with a Televue TRF-2008 x0.8 Focal reducer.  The camera is mounted on the Starlight Xpress filter wheel via a T-adaptor screw fitting, then into the Focal Reducer, which fits the other side of the filter wheel using another T-adaptor thread.

I managed to get 12 x 10 minute exposures over the last 2 clear nights, and also have started on some 5 minute colour data for fun as well.  Here is the result so far.  That is a satellite in the Green data, giving the streak.  I am not sure which one, but might try and track it down.

The Iridium satellites are used for satellite phone calls.  They are named because it was originally intended to launch 77 satellites providing call coverage around the globe.  However, it was determined that all 77 satellites were not needed to provide full worldwide coverage, so there are currently 66 operating satellites in orbit, with 6 spares in a holding orbit. The orbital height of the operational satellites is 485 miles on average.  They are travelling at 16,832 miles per hour, and complete one orbit of the Earth every 100 minutes.

The reason for the flare seen in the picture is that these satellites have 3 door-sized antennas angled at 40 degrees away from the main body of the satellite itself.  They are arranged equally, with 120 degrees between them.  When the light from our Sun hits the antenna, about 4-5 times a day the reflected light create a 6.2 mile wide circle of light on the surface of the Earth.  To an observer, this appears as a bright flash of light which suddenly gets brighter, then dimmer as the satellite moves over their head.  The date and time of each flash is easily predictable, as the orbit and attitude of the satellite is known precisely.

To find out whether I had accidentally caught an Iridium flare, and check which satellite and antenna  my camera saw the reflection from, I checked on http://www.heavens-above.com, which provides detailed prediction for most satellites circling the Earth, including the International Space Station and Iridium Flares.

I was able to determine exactly which satellite I had captured - Iridium 72 - and the reflection was from the front facing antenna (its direction of travel).  At the time of the flash, the satellite was 640 miles away.

Here is the track of the satellite from Heavens-Above.com showing the predicted position of the flare:

I PDF'd a version of the Flare information from Heavens-Above.com, which you can download here.

This year, I decided to see if I could take a picture of the whole of the Veil Nebula.  My camera (SXVR-H18) and telescope (101mm @ F/7) combination can only see 1.4 x 1.1 degrees at F/5.6 with my Televue Focal Reducer, so to get the complete veil requires taking images of different areas of the sky, and stitching them together.  You can see the boundaries of the panes in the image above.  Each 'pane' is the result of stacking many images together.  So far there are 97 images making up this mosaic.  So far, I have been concentrating on the Hydrogen emission wavelength with my Ha narrowband filter.

This will be a several year project, as I then need to shoot with an Oiii (Oxygen) filter, and then choose whether to shoot with an Hb (Hydrogen Beta) or Sii (Sulphur).  I might even be able to incorporate some of the data from previous imaging runs - time will tell.  I have some gaps to fill in the Ha band - I just need some clear nights!

Here are some of the other pictures I hope to incorporate should the inclination take me:

NGC6992/NGC6995/IC1340 is known as the Eastern Veil, or Network Nebula
NGC6992 is the bright area, NGC6995 is the 'rectangle' element of the Eastern Veil Nebula.  Between the Eastern and Western Veil, Pickerings Wisp is the fainter triangle shaped structure
NGC6960 is known as the Western Veil, Witches Broom, Finger of God, of Filamentry Nebula

At a distance of 1,470 light years away, the Veil Nebula is the result of a supernova which is thought to have exploded 5,000 to 8,000 years ago.  The resulting gas and dust released spread out into this 3 degree area of sky (roughly 6 times the diameter of a full moon) in the time since the explosion.  It is one of the largest, brightest features in the X-ray band.  The dust and gas is estimated to be travelling at the huge speed of 370,000 miles per hour away from the original star which spawned it.

Read more about the Veil Nebula and see a beautiful picture from the Hubble Space Telescope here: http://www.space.com/4136-veil-nebula-pierced-hubble-gaze.html

Subject: [vsnet-alert 16812] Re: PSN J09554214+6940260: bright (11.7 mag) supernova in M82
At UT 2014 Jan 22.305, we obtained a spectrum of PSN_J09554214+6940260 (discoverer: S. J. Fossey) with the Dual Imaging Spectrograph on the ARC 3.5m telescope. We classify this as a Type Ia supernova with a Si II velocity of 20000 km/s. The best superfit match is SN2002bo at -14d. The supernova has a red continuum and deep Na D absorption.

A type 1a supernova is what happens when a binary star system starts to tear itself apart.  In essence, a very small dense white dwarf rips the material from the surface of its neighbouring star.  It appears to be relatively common when one of the stars in a binary star system inflates when it becomes a red giant.  The surface of the red giant is now much closer to the companion star, and so matter starts to transfer from the red giant to the smaller star.  As the smaller star accepts matter from the giant, the system becomes unstable, and the small white dwarf explodes violently.

The velocity quoted above shows that the shockwave of this star exploding is travelling at 20,000 km/s - thats almost 12,500 miles per second - pretty quick.

Type 1a supernovae are special because they allow astronomers to accurately gauge the distance from the Earth of the galaxy that spawned it.  Each one that is identified gives astronomers much more accurate data about the Universe around us.

I managed to gather a quick snap of Messier 82 tonight before the clouds rolled in.  This animation shows the difference between some Messier 82 images I took last year in February versus the 2 exposures I managed to capture tonight.

You can listen to some of the old episodes here

This episode of the Sky at Night was dedicated to the LCROSS lunar impact (http://lcross.arc.nasa.gov) event on the 16th October, and was broadcast in November 2009. I was asked to come along and setup my scope at the seaside to try and capture the impact, unfortunately, cloud prevented us from seeing anything. The good news was that no-one else did either, as the impact was not visible from Earth!

The Sky at Night - January 2010

This episode was filmed in December 2009. I was asked to come along and bring some imager friends, so I invited Neil Richardson, Stephen Green and Iain Melville. I also took Emily along as well.  We had a great time filming, and also got some imaging in as well. Iain taught Emily how to do Star Trails with my Canon 350D, and caught some beauties.  More of her work here: Emily's Star Trails

Here is the video, Emily and I are on at 1 minute 30 seconds: https://youtu.be/UbIcwvYTih8