Tuesday, November 26, 2013

Observatory Guest Nights at Montgomery College

Sorry if this post rambles a bit! As we gear up for a more regular schedule of guest nights, I wanted to give a little history and perspective about how we got here.

When I was hired by Montgomery College the summer of 2009, construction of the new Science Center on the Rockville campus had just begun. It looked like this:

Photo credit to Montgomery College
During my interview I was told there would be a new observatory (in addition to the two telescopes on top of Macklin Tower!). The observatory was one of the main reasons I decided to join the college.

By June of 2010, the new observatory was taking shape:

Observatory June 2010

And by August 2010, we had walls and a roof:

Observatory August 2010, view from Macklin Tower


It wasn't until October of the following year that we were ready to install the scopes. In the photo below, the Astropiers are just sitting on the ground and I'm testing the data connections. The scopes were mounted on the piers shortly after.

Observatory October 2011

The first observatory public nights I hosted were at the Macklin Tower observatory before construction was complete on the roof of the Science Center. We ran these events in a true open house style. That is, we would open for a couple of hours and guests would come any time during that two hour period. We kept to a regular schedule of first and third Fridays of the month, weather permitting. Once the new observatory was ready for guests, we took the same approach.

Happily, the public nights were a success. We had a good showing of guests from the college and local community. We were so successful in fact, that we were in danger of exceeding the fire marshal occupancy limit!

What to do?

I decided to try out the paradigm used by the UNC Chapel Hill Observatory. (I was a graduate student at UNC and telescope operator for the guest nights during my time there.) The dome at UNC can accommodate only a limited number of people, so the event was reservation based. It used to be that guests would have to call the physics department to reserve a space. The event would be rain or shine. If the weather prohibited viewing, we would give a talk and simply show the telescope.

So here we are. 

I've run a grand total of two guest nights using the reservation paradigm, similar to what we did at UNC. With the support of the Physics & Engineering Department and college administration (thanks!), as well as the dedication of the MC Stargazers club (major thanks!), we're going to give this method a go on a regular schedule.

Were going back to first and third Fridays, as long as the college is open.

As we transition to this new approach, I'd like to thank you for your patience and understanding. We're working to make the observatory nights a fun, educational, and engaging experience for everyone. Suggestions are welcome. All of us involved in putting together these events do so on a volunteer basis. (Myself included- I'm a full-time faculty member and any observatory work is in addition to my duties as an associate professor.) It's definitely a labor of love. There are few things I enjoy more than sharing what I know about the universe.

The new schedule is posted on the Event Schedule page. You can make reservations via EventBrite here. My contact information is here. Please feel free to let me know how we can make the observatory nights better, as well as letting me know the things you really like about the events!

Looking forward to seeing you at the observatory.

-carrie

Roof upgrade

The work hardly took any time at all. The gates on the roof have been modified. Check it out:

Monday, September 2, 2013

Hottie Pixels and Processed Images

I've been lazy about image processing. To get nice astro images, it takes more than aligning and summing multiple images. Why?

CCD images have artifacts.

Here are the problems:

  1. Hot pixels - These are bright dots that appear in the same spot on each image.
  2. Vignetting - This is uneven illumination of the field.
  3. Dust spots - These end up looking like unfocused blobby blobs.
  4. Noise - Read noise is what gives a grainy appearance to an image.

Above: M57 (Ring Nebula). 15 2-second exposures with Opticstar CCD on 14-inch w/ focal reducer. Fully processed.

What to do? Let's start with the noise. Electronic noise can be subtracted out with a "bias frame". A true bias frame is an image of zero exposure time where the CCD is read out without having been exposed to any light (scope is covered). This allows you to isolate the effect of read noise. The shortest exposure time I can get with camera control software I have (Nebulosity) is 10 ms (0.01 seconds), so this is what I use for my bias frames. It's best to take many bias frames and average them to make a master bias frame.

Above: M31 (Andromeda Galaxy). 20 2-second exposures with Opticstar CCD on 14-inch w/ focal reducer. Fully processed. This galaxy is 2.5 million light years distant!!

To get rid of the hot pixels, you use a "dark frame". This is simply an image with no illumination (again, the scope is covered) taken under the same circumstances as your real astro image. Darks should be taken the same night the real image is taken. It's considered good practice to take about the same number of exposures and same exposure time that you have of the real image and average them into one happy dark frame.

Above: M15. 20 2-second exposures with Opticstar CCD on 14-inch w/ focal reducer. Fully processed.

To minimize vignetting, you use a "flat frame". Flat frames are images with an even illumination. You can use the sky at twilight or a white screen. The recommendation is to take several flats and combine them. The software I use (Nebulosity) scales the intensity of the flats, so the exposure time isn't so important. I use the same exposure time for the flats as I do for the real images.

The flat frame should be pre-processed, that is you should subtract the dark frame and the bias frame from the flat.

The Nebulosity software has a processing algorithm. All I have to do is combine the dark frames and bias frames, and pre-process and combine the flat frames.

Above: My flat frame. Combination of 30 2-second exposures. Telescope was pointed at a white posterboard.

In summary:

To minimize read noise, subtract the bias frame from your real image.

To remove hot pixels, subtract the dark frame from the image frame.

To minimize vignetting, divide your real image by the flat frame.

Or, in equation form:

Good = (Raw - Dark - Bias) / (Flat - Dark - Bias)

The processing equation above is applied to each of the real images. Next the images are aligned and combined. Once again, Nebulosity has an algorithm for aligning and combining. For each image you select two stars, and the software will translate and rotate each image before they are combined.

Saturday night I took dark frames, flat frames, and bias frames. I also took more exposures of each image. I think the images are looking better!

Sunday, August 25, 2013

The Queen, the Dragon, and the Flying Horse

Finally, a gorgeous and clear Saturday night, and my first chance to test out the new focal reducer. Long story short, it's awesome.

My life will never be the same.

It is simply fabulous to be able to fit M13 (Hercules Cluster) on the chip. It's like having skinny jeans for a telescope. Maybe that's a bad analogy. Anyhow, I took a few images of the bright globular, but honestly, they were sort of meh. I've gotten better results with the Canon Rebel DSLR attached with a T-mount. But still, happy dance because M13 fits!

Here's M13 w/ the focal reducer (it's not too bad):

M13 w/ Opticstar DS145C on 14-inch, 6 2-second exposures stacked

The scopes were well behaved (no alignment issues) and I therefore had lots of time to spend actually looking at objects. Here's the rundown of what I saw by constellation:

The Queen (Cassiopeia)

  • NGC 457 (a.k.a the Owl Cluster, the ET Cluster, or Caldwell 13) is an open star cluster about 7900 light years distant and approximately 21 million years old. Discovered by William Herschel in 1787.

    NGC 457 w/ Opticstar DS145C on 14-inch, 6 2-second exposures stacked
  • M103 (a.k.a. NGC 581) is an open cluster between 8000 to 9500 light years distant and about 25 million years old. Discovered in 1781 by Pierre M├ęchain.

    M103 w/ Opticstar DS145C on 14-inch, 6 2-second exposures stacked
  • M52 (a.k.a. NGC 7654) is an open cluster with an uncertain distance between 3000 and 7000 light years and an estimated ate of 35 million years. Discovered by Charles Messier in 1774.

    M52 w/ Opticstar DS145C on 14-inch, 6 2-second exposures stacked

The Dragon (Draco)

  • NGC 6543 (a.k.a. The Cat's Eye Nebula) is a planetary nebula. I was super excited to see it, but it didn't photograph well. It's small and faint. Basically it looks like a fuzzy little star and of course nothing at all like the Hubble images.

The Flying Horse (Pegasus)

  • M15 (a.k.a. NGC 7078) is a globular cluster estimated to be about 12 billion years old. (One of the oldest globulars!) It was discovered by Jean-Dominique Maraldi in 1746.

    M15 w/ Opticstar DS145C on 14-inch, 7 4-second exposures stacked

Overall, I think the astrophotography is getting a little easier, and a maybe just a little better with each attempt. The major lesson learned from these images is that I really need to take more, and perhaps longer exposures.

I need more photons.

Thursday, August 15, 2013

Focal Reducer

I've played around with our Opticstar CCD cameras enough now that I feel limited by their relatively small field of view (FOV). For the 14-inch telescopes the FOV w/ CCD is approximately 8 x 6 arcminutes. Saturn and the Ring Nebula (and other planetary nebulae) fit just fine, but I'd also like to image larger objects, like globular clusters.

The easy solution is a focal reducer. We recently purchased what seems to be the only focal reducer in the universe that will work with our CGE Pro EdgeHD telescopes. It's a beast of an accessory at 3.25 pounds, so today we balanced one of the scopes with the focal reducer and camera.

The reducer will reduce (go figure) the the focal length by 0.7. By my calculations, the new field of view (for the CCD camera) should be about 12 x 9 arcminutes. It's not a huge gain, but it will allow me to fit globulars like M10 and M12 (constellation Ophiuchus) in the field. The Hercules Cluster, M13, may be too big, but I'll likely try to image the core anyway.

Focal reducer at base of 14-inch w/ Opticstar CCD camera
BTW, I calculated the FOV in arcminutes using this:

FOV = (S x 3438) / f

where S is the size of the CCD chip in mm, and f is the focal length of the telescope in mm. Exciting, I know.

I don't plan on changing out the focal reducer anytime soon since balancing the scope is a pain in the keister. What will the FOV be with a regular eyepiece? A rough calculation gives me 32 arcminutes for our 26 mm eyepiece and 44 arcminutes for our 40 mm eyepiece. Big, but not quite big enough to fit the 60 arcminute Brocchi's Cluster. We may have an eyepiece (a Panoptic?) with a larger apparent FOV, though. I'll have to check.




Nice night, but no pictures

Last night was absolutely gorgeous. I made it to the observatory a little before 9pm. My mission was to re-align the east 14-inch scope. It was being fussy during the observatory beta test. The scope aligned just fine, and tracked well. I played around a bit, bopping here and there, but didn't do any photography. With a first quarter Moon and a tiny amount of haze, the sky was a bit glowy.

I spent some time looking for the possible nova in Delphinus. I think I found it, but since it looks like a regular magnitude 6 star, I can't be certain. On the bright side, I did find a faint planetary nebula (also in Delphinus), NGC 6905.

Monday, August 5, 2013

Observatory Beta Test

We had a clear night for the observatory open house beta test. We were able to see Saturn, M57 (the Ring Nebula), NGC 6826 (the blinking planetary),M13 (Hercules Cluster), and Albireo (double star system in Cygnus, well actually a triple star system, but we can only see two).

I had hoped we'd somehow get to take more pictures, but alas, we only snapped a few of the Albireo system.

Lots to think about before the next open house.


Friday, July 26, 2013

Clouds!

I arrived at the observatory around 8:30 PM, and the sky looked reasonable with just a few clouds on the southwestern horizon. Unfortunately the situation has not improved. The satellite doesn't look promising either.

I took some flats, with the DS145C, but looks like I won't have much use for them tonight. *sigh*