Observing Log for Friday 21 October

What a fabulous night with clear skies and delightfully cool fall air. Below is a summary of what we observed last night.

• Jupiter : Heat coming off the roof made the image a little fuzzy, but we were able to make out cloud bands on the planet as well as all four Galilean satellites- Io, Ganymede, Europa, and Callisto.
• Saturn : Saturn looked lovely and we were easily able to see the moon Titan. Rhea, Dione, and Tethys were fainter, but also visible.
• M57 (the Ring Nebula): This fine example of a planetary nebula appeared as a delicate smoke-ring in the eyepiece of the 8-inch scope.The Ring Nebula is located in the constellation of Lyra and is about 2,300 light-years from Earth. Planetary nebulae are the remnants of lower mass stars (like our Sun) after they've used up their nuclear fuel.
• M31 (Andromeda Galaxy): We looked at the Andromeda Galaxy in the 14-inch. This object is a neighboring galaxy located about 2.5 million light-years from us. It's a spiral galaxy like our own Milky Way, but it's larger. M31 is about 220,000 light-years across compared to the Milky Way's 100,000 light-year diameter. Through the telescope M31 looked like a small fuzzy ball with a star-like center. The bright center is the core of M31 and the fuzziness is the light from the hundreds of billions of stars that make up the galaxy.
• The Albireo System: Through the 8-inch, we observed this double-star in Cygnus. The stars of Albireo (one blue, one gold) can't be resolved with the naked eye, but through our telescopes we are able to see the pair. The brighter yellow star is also a binary system, but these two stars are two close for our telescopes to resolve. Albireo is about 430 light-years distant.
• NGC 6826 (the "blinking planetary"): NGC 6826 is planetary nebula located in the constellation of Cygnus. It's called the blinking planetary because when you have it centered in the eyepiece, it appears to blink "on" when you look away from it and "off" when you look directly at it. The effect happens because our peripheral vision is more sensitive than our forward vision.

Sincere thanks to Stacey and Harold for making the evening a success!

And as always, thank you to everyone who attended. Your presence and enthusiasm fill me with happiness.

Observing Log for Friday 20 September 2019

This was our fifth observatory night in a row that wasn't clouded out! Woo hoo!

Earth hasn't moved that much around the Sun since our last event (and the one before that), so the observing log is the same as it has been, save for the Andromeda Galaxy. Here's what we saw:

• Jupiter : Heat coming off the roof made the image a little fuzzy, but we were able to make out cloud bands on the planet and three of the four Galilean satellites- Europa, Ganymede, and Callisto. Io was behind Jupiter and not visible while we were watching.
• Saturn : The lovely ringed planet was also a little low, but even still, we could make out the brightest of its moons (Titan, Rhea, Dione, Tethys, and possibly Enceladus.)
• M13 (the Hercules cluster): Next we looked at the globular cluster, M13. M13 can be found in the constellation of Hercules and is about 22,000 light-years from Earth. There are about 150-160 globular clusters located in the halo of our galaxy. These clusters contain some of the oldest stars in the Milky Way.
• M57 (the Ring Nebula): After M13, we headed to M57. The Ring Nebula is located in the constellation of Lyra and is about 2,300 light-years from Earth. Planetary nebulae are the remnants of lower mass stars (like our Sun) after they've used up their nuclear fuel. The Ring Nebula appeared as a delicate smoke-ring in the eyepiece.
• M31 (Andromeda Galaxy): We looked at M31 through the 8-inch scope on the deck. This object is a neighboring galaxy located about 2.5 million light-years from us. It's a spiral galaxy like our own Milky Way, but it's larger. M31 is about 220,000 light-years across compared to the Milky Way's 100,000 light-year diameter. Through the telescope M31 looked like a small fuzzy ball with a star-like center. The bright center is the core of M31 and the fuzziness is the light from the hundreds of billions of stars that make up the galaxy.
• The Albireo System: We finished the night with a double star in Cygnus. The stars of Albireo (one blue, one gold) can't be resolved with the naked eye, but through our telescopes we are able to see the pair. The brighter yellow star is also a binary system, but these two stars are two close for our telescopes to resolve. Albireo is about 430 light-years distant.

Sincere thanks to Iadviga and Ryan for their assistance with the event.

And as always, an astronomical-sized thank you for everyone who attended. Your enthusiasm for the night sky is a joy to witness!

Upcoming events, guest night recap, and some links

Yesterday evening was our last official observatory guest night of the season, but there are a couple of other upcoming events that we'll be participating in:

This coming Monday 19 October, we'll be hosting a satellite event for the 2015 White House Astronomy Night at the Montgomery College Planetarium on the Takoma Park / Silver Spring campus. Details are here. Dr. Harold Williams and I will be there with students from MC's Engineering and Science Adventure Club and the MC Stargazers.

On Saturday 14 November we will be bringing a couple of our telescopes to the Croydon Creek Nature Center for a star party. To register, go to events (menu on the right-hand side of the screen), and then scroll through the dates until you get to 14 November.

Here is a recap of what we observed last night:

Through the 14-inch scope

• Albireo (double star in Cygnus)
• M57 (planetary nebula in Lyra)
• M31 (Andromeda Galaxy)
• NCG 6826 (The "blinking planetary" in Cygnus)

Through the 8-inch scope

• Waxing crescent Moon
• M13 (Hercules globular cluster)
• Epsilon Lyrae (a multiple star system in Lyra)

Last night I recommended several astronomical links to different folks. First, here's the link to the planetarium software package Stellarium. Stellarium is free and operates on Windows, Mac, and Linux. I've used it on all three platforms without issue. There is a mobile version ($2.49, last time I checked) as well.

I also use the website Heavens Above for astronomical and satellite data.

Finally, the US Naval Observatory's Data Services page is a fantastic resource and one I use frequently.

A clear evening for this past observatory night

It's been awhile, but we had clear skies this past Friday. We observed the following objects:

Through the 14-inch scope

• Albireo (double star in Cygnus)
• M13 (Hercules globular cluster)
• M57 (planetary nebula in Lyra)
• M31 (Andromeda Galaxy)

Through the 8-inch scope

• Saturn
• Waxing crescent Moon

Binoculars

• Waxing crescent Moon
• Brocchi's Cluster
• Antares (taking note of the twinkling from atmospheric turbulence)

Many thanks to Kim and Ryan for operating the 8-inch telescope and binoculars, respectively, and thanks also to the MC Stargazer club members. These events would not be possible without the time and talent of Montgomery College students.

The next two events are full, but we've added a wait list to the Eventbrite ticket reservations. If you are on the wait list, you will be notified by email if a slot opens up.

The MC Stargazer's club is planning to do some daytime solar observing events on the Rockville campus this coming October. I will post information when we have the details.

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!