Exposure vs Linearity

March 14, 2019

Astrophotographers 'hate' sky background at night time. This is worst in cities of course with all the street lights, Billboards and what not. We live on the ground and we light up the sky only because we are careless.

Here is a simple data from a series of images i took from my observatory. Starting from 1 sec and doubling the exposure with each image; these are seven in total.

Celestron C14, SBIG ST9XE CCD camera, Astrodon Luminance filter (and more) was used to acquire this data.

Notice a perfect linear relationship here (notice R^2 value). CCD cameras have excellent linear response to star light photons and here, sky background photons. This is the reason we like CCD's or CMOS for that matter (until they remain linear). CCDs are always better than CMOS.. there are many reasons for that.

I have attached a short clip of these seven images as well.. you will see very few stars in a single second exposure and many more with increasing exposure. Telescope was not being guided so you will see black bands in the images; this is the result of aligning unguided exposures.

Sun in Halpha Telescope - 27 January, 2019

January 27, 2019

Sunday is the only day when i can do anything with my solar telescopes. So today was a blessing when the sky was clear. I have Lunt 152 Halpha telescope which shows the atmosphere of our Sun so nicely.

With ZWO 174 mono camera and imaging at 130 frames per second helps a lot to find the sharpest moments in the earth’s atmosphere which is always a problem for high resolution solar/planetary Imaging.

Above image is the stack of 4000 sharpest from about 20,000 frames. AVIStack, Registax and Photoshop was used to produce this image.

M3 Globular Cluster

January 23, 2019

500,000 stars held together, some 35,000 light years away from us, with almost 300 variable stars is known as M3 Globular Cluster. This deep sky object is probably the one which caused Charles Messier to start logging nebular objects in the sky.

Equipment: Celestron C14 + SBIG ST9XE + Astrodon I photometric filter

Exposure time: Subs of 60 seconds (so the core does not get over exposed) totaling 75 images.

Satellite passing right in the middle of a beautiful galaxy

January 17, 2019

This is not a recent image. The galaxy here is the famous, M63 or Sunflower Galaxy. Since most night sky objects are very very dim; astroimagers expose their camera with the starry photons for minutes or even hours (if the sky permits).

While imaging M63 at 5 minutes of single exposure, here came the image.. a satellite had just passed right through the center of the galaxy! Of course the satellite was in the foreground and the galaxy is way way too far from us.

Now that’s an interesting image!

Famous Asteroid 433 Eros

January 14, 2019

Asteroid 433 Eros is famous because in 1998 Space Probe NEAR Shoemaker visited it and gave us stunning views of this asteroid.

The above image is a stack of 263 images; each image was of 5 seconds exposure in luminance filter. Telescope was being tracked but not guided. The Asteroid was moving from right side of this image to left. The time of image acquisition was 30 minutes.

Top right has a beautiful close visual binary star which are almost 9 arcseconds distant from each other and both have about 7 magnitude brightness. Hipparchus Star Catalogue has it with an entry as HIP 21108.

Milky Way from a hill station

January 13, 2019

Few years back, i went to Nathia Gali and took my DSLR, Canon 6D with me. I had recently purchased Rokinon 24mm lens which can operate at f/1.4 and also has a lens to correct spherical aberration.. a great lens for wide field low light imaging tasks, namely our own galaxy Milky Way.

Above is a stack of multiple 30 seconds exposures. I had just put the DSLR on a chair and lens was looking straight up in the sky and this is what it saw. Of course this image has gone through Photoshop.. we cant live without PS can we! All the colors are true in this image.. just enhanced a bit.

NGC 1788 - A reflection nebula in Orion

January 10, 2019

Orion is dominated with many Deep Sky Objects; the crown is of course the most imaged nebula, M42. In the same constellation lies a reflection nebula which is cataloged as NGC 1788.

It is 1300 Light Years away from us and is located about 5 degrees North from Rigel. It contains extremely young stars and shines with the reflection of these stars’ light.

Image details:

Telescope: Celestron C14

Camera: SBIG ST9XE

Filter: Astrodon Luminance

Mount: Losmandy Titan

Guiding: Autoguided with SBIG Adaptive Optics at 6.4 Hz

Sub Exposures: 5 minutes each

Total Exposure time: 100 minutes

I do need to collect more photons from this object which i will in coming nights. I will also image this object in Infrared band.

Oh and btw, i have shrunken the fat stars in the picture :)

NOMAD shows that at my location with Luminance filter i can go a bit beyond 18 magnitude around 50 degrees altitude south side.. it is two magnitudes deeper than my previous location.

Above is the graph of autoguiding errors from The Sky X Pro.. Left side is the latest. Notice the ‘Guide Star’ was behaving a lot better a while ago but it started to jump all around before i stopped the imaging run. This happened because the Seeing got worst!

Solar Outreach at Science Festival Faisalabad

May 7, 2018

Solar Outreach at an orphanage at Islamabad (April 28, 2018)

May 7, 2018

Solar Outreach at LGS 1A1 School (April 26, 2018)

May 7, 2018

Basic Astro-Imaging talk at LUMS (April 20, 2018)

May 7, 2018

SPADES is a Science & Engineering society at The Lahore University of Management Sciences. They organised a symposium on Astronomy where i talked about basics of Astro Imaging.

Bit of a Media exposure

May 7, 2018

Solar Outreach in UMT University

April 19, 2018

Solar outreach at UMT today in Lahore. Started with delivering a presentation on our Sun and how to see it safely and then moved out in the ground for the observation session.

Some 100 people showed up.. asked many good questions!

Temperature dip in the observatory after opening the roof

April 18, 2018

Upper Graph: Inside observatory temperature Lower Graph: Outside observatory temperature — Upper Graph: Inside observatory temperature
Lower Graph: Outside observatory temperature

So the highest temperature today went to about 35 C. I kept the roof of the observatory closed and opened it around 22:30. Notice the sudden dip in the upper graph. This shows the sudden release of the heat trapped inside the observatory even after 4 hours of sunset and then the heat loss ratio became stable.

Lower graph shows the temperature loss outside the observatory.. of course no sudden dip around 22:30.

Solar Outreach in UET University

April 18, 2018

UET Science Society invited us for a Solar Outreach activity at UET, today. Not many people came there, it seems the event was not publicized and organised.

We did enjoy, talking with those who came there!

Solar outreach in LGS EME School

April 12, 2018

The weather is getting hot now.. In the direct sunlight, it is getting hard to stand and keep talking to hundreds of students.. of course, who cares about that!

Today i met super charged students of LGS EME branch.. Some 400 kids from 6th and 7th grade. They saw the Sun through Solar Glasses donated by CBSAP and my Lunt 152 Hydrogen Alpha Solar telescope; i use this scope with B3400 which gives a bigger field of view of the Sun.

They were shooting questions about every thing they could think of in the entire Universe.. Extra-terrestrial life forms, Black holes, Alien planets, Formation of Stars, planets and moons, Space Missions and what not! I was speaking at the maximum possible speed my sound system could manage with continuously taking water to keep it running. At the end of it all, some 3 hours later, the sound system broke and i am very very happy with that!

Students of LGS EME, you are great!

Strong Winds at Zeds Observatory

April 8, 2018

This is the graph from my Weather Station at the observatory.. Upcoming three days are predicted to bring thunderstorms.

The following is the highest wind speed recorded at the observatory last year.

The blue line is indicating rain here.. Red line are clouds and the yellow is daylight.

LAST's April 2018 Monthly Meeting

April 7, 2018

Lahore Astronomical Society meets every first Friday of every month, except Ramadan. This month it was yesterday where Schehrzade Syed gave a presentation on Life of late Stephan Hawking and his most famous works. It was extremely entertaining and there were many video clips embedded. I felt like i was meeting with the family & friends of Hawking through the entire presentation.

Good job Schehrzade!

Solar Outreach at COMSATs

April 4, 2018

Being under the burning sunlight, standing for hours, constantly talking to hundreds of people, continuously repeating every time to a new observer what to see, how to see and what is being seen.. this all does not drain me at all; On the contrary, it gives me such energy which i cannot explain in mere words.

Just give me a crowd.. hundreds? yes.. thousands? even better! I have been doing it for decades and will do it everyday.. all my life!

Today i went to COMSATS, Lahore and took my Hydrogen Alpha Solar Telescope with me, CBSAP Glasses and spectral rings. Alpha who is new to our Astronomical Society's core group also came and helped a lot!

Gassendi Crater

April 2, 2018

Pierre Gassendi (1592-1655) was a french philosopher, priest and mathematician. He explained parhelia, measured the speed of sound with some accuracy, became the first person to observe the transit of a planet (Mercury) across the Sun. (Wikipedia). He also corresponded with Galileo and was a strong beliver of Copernican system.

The big crater on the right in the image is named after Pierre Gassendi.

Gassendi crater is located on the western limb of the moon (in the right image, an arrow is pointing to this crater). Right below this crater is Mare Humorum (Sea of Moisture), a 389 km diameter impact basin.

A small portion of North-West Rim of the basin of Mare Humorum is visible in the image.

Gassendi A & B Crater:

Gassendi A is a 32 km sized crater which has impacted on the northern rim of Gassendi crater, which resulted in destroying that part of the rim and raising of the northen floor of Gassendi. Gassendi A was once called Clarkson but IAU does not recognise it with this name.

Gassendi B is 25 km wide and seems much older than Gassendi A due to its rounded rim. Also there is a peculiar secondary rim near the eastern rim of Gassendi B, which starts from the base of the bigger rim goes straight down to South for 77 km and then terminates. But it seems a faint one going towards SouthWest side.

Gassendi Crater:

Now coming back to the star of the show, the main crater Gassendi. It seems a bit oval in shape but that is due to its placement on the moon where moon's spherical shape changes the viewing angle from circle to an oval.

Compare this picture with the image from LRO lunar orbiter which shows its true circular shape.

Gassendi is an old crater, estimated to be around 4 billion years old. Although the floor of the crater is all fragmented but it seems that it was flooded, probably from the Mare Humorum. There are many central peaks in the center and the highest is 1.2 km tall.

The walls of the crater seems intact everywhere so perhaps the lave came under the walls?

Mare Humorum seems to be the source of this lava. Note the southern part of Gassendi, where Mare is located, is distinctly smoother than the rest of the crater floor.

Also the Southern most rim is also the weakest part of the entire rim. Other parts of the rim have no terrace structure which is easily visible in other big craters such as Copernicus. This is probably because of the moon quakes or the impacts near Gassendi, specially Gassendi A, that the terraces have disappeared form the rims.

Gassendi Floor Structure:

Gassendi has probably the most complex rille (narrow channel) structure of all the craters we can see on the moon. A huge contrast is Plato. I have drawn some rough lines of this rille pattern in yellow so it can be seen a bit easier. These rilles are probably a few hundred meters deep. These rilles are believed to be formed by the collapsed lava tubes or extinct lava channels. A lot was once happening at Gassendi!

Another interesting area is this crater to the west of Gassendi. This crater has a marked bright ejecta in its surroundings. The crater is 2.5 km wide and the ejecta is more than 10 km wide.

North West area of Gassendi is very uneven and has various smaller craters. Gassendi was once a potential target for Apollo 17 mission because it can offer highlands as well as the material from the Mare. But it was too difficult to move around so they went to Taurus-Littrow Valley.

Gassendi is also very famous for a rare phenomenon noticed by avid lunar observers, called Transient Lunar Phenomenon (TLP). They report a sudden brightness of light and color in and around Gassendi.

Image Acquisition:

Here is an overview of how i took this image:

Telescope: Celestron C14 with 2.5X Powermate

Camera: ZWO ASI 174 mono with Red Filter

Mount: Losmandy Titan

Processing: Stacked 2,000 frames from 25,000.

Autostakkert, Registax, PS.