Bright nebulae at Milky Way core

Summer views of Milky Way are spectacular because the galaxy bulge is brighter and broader than its spiral arms visible the rest of the year. Located near Sagittarius and Scorpius constellations, the bright nebulae and dark lanes of the area creates a beautiful contrast in brightness and colors.

This picture is a 4-pane mosaic ensambled with free software Fitswork 4.40. Every pane is a 10 minutes exposition through a 55mm lens attached to a Canon EOS 450d (Rebel XSi) DSLR camera, mounted over a motorized equatorial mount, Sky Watcher EQ6.

A full resolution picture is available at AweSky

EQ6 periodic error

I took a bunch of 30 seconds shots aiming M42 nebula as regular, in order to stack them later. Polar alignment was also regular, using EQ6 polar scope, probably not perfect.

I think M42 is a good target to measure periodic error in RA movement due to its near 0 degrees declination.

In order to show the drift, I stacked the shots without drift correction using a free software called startrails that gets the brightest pixels per shot, obtaining that way the best startrail you can achieve.

To measure the length of the drift, I requested a single shot solved plate from astrometry.net. They provide an exact width in arcminutes of the field. Then, I divide the width field by the width in pixels of my DSLR camera sensor, obtaining the resolution per pixel in arcseconds (a number close to 1 arcsecond/pixel for a 1,200 mm effective focal length telescope).

Then I measure the height of RA drift pattern with my regular post-processing free software, Fitswork4, and multiply that value by the previous resolution.

That is the way I have found that my EQ6 mount drifts around 40 arcseconds in RA movement. Dividing total exposure by the number of cycles (top peak to lower peak) I got the elapsed time needed to fulfill the periodic error: around 6 minutes long.

North America Nebula

This picture of North America Nebula (NGC 7000, a bright nebular region located in the Milky Way area of Cynus) was taken yesterday, 2010-11-03 under good transparency skies, using a 55mm lens and Canon EOS 450d, Rebel XSi and an EQ6 mount doing the unguided tracking. This is just one shot of 1380 seconds of exposition (23 minutes).

Postprocessing done using PSP9 and Fitswork4.

NGC 7000 is an emission nebula in the constellation Cygnus, near Deneb (α Cygni), also called the North American Nebula. The dark central region called the Gulf of Mexico, as in some astronomical plates for many years resembled that region of America.

Nebula NGC 7000 is the largest covering an area equivalent to the full moon, but its low surface brightness does not normally visible to the naked eye (though, in a dark, using a UHC filter can be seen without optical aid) NGC 7000 and the nearby Pelican Nebula (IC 5070) are part of the same interstellar cloud of ionized hydrogen (HII region). The dark area in the center is a very dense region of interstellar material in front of the nebula and which absorbs light of it, giving the group its characteristic shape.

It is not known with precision the distance that separates us from NGC 7000, neither the star responsible for the ionization of hydrogen that results in the emission of light. Supposing Deneb is the star that illuminates the nebula NGC 7000 then the distance to Earth is on the order of 1800 light years.

Capella, the brightest star in Auriga

Capella is the brightest star in Auriga constellation. It is very easy to spot in the Northern hemisphere. It is a circumpolar star, very bright one. The picture has been taken through a 300mm telephoto lens and Canon EOS 450d over a Sky Watcher EQ6 equatorial mount.

Here it is the full frame, with a lot of stars in the field and great detail:

http://www.awesky.com/Deep+Sky/Misc/Capella+-+Alpha+Aurigae/

M57, the Ring Nebula

The Ring Nebula (also known as the Planetary Nebula M57, Messier 57, M57 or NGC 6720) is a prototypical planetary nebula in the constellation of Lyra. This is one of the most famous nebulae often used as an example of this type of astronomical objects. It is located at 0.7 kpc (2300 light years) from Earth and was discovered by Antoine Darquier de Pellepoix in 1779.

Their joint magnitude V-band (green filter) is equal to 8.80. Its real form is possibly a bipolar nebula seen with an inclination of 30 ° from its axis, and calculated that it has been expanding around 1600 years.

From their radial velocity, -19.2 km/s, it follows that approaches Earth more than 69120 km/h: this rate is caused by the combination of the sun’s orbital speed around the nucleus of the Milky Way and the speed of the Earth itself.

M57 is illuminated by a white dwarf at its center of visual magnitude 15.8.

This picture is a single shot of 30 seconds exposition through a SkyWatcher 6 inches refractor telescope at prime focus. Fitsworks4 was used to remove a bit the background noise.

M101 with 300mm telephoto lens

This is a crop of the resulting stacking of 36x30s + 2x360s subframes taken this month in two different sessions. The area showed corresponds to M101 and surroundings (in Ursa Major), in which we find other 2 galaxies NGC 5474 and NGC 5477. Below, I have added a DSS2 image of the are for comparison. My stars are blobs, meanwhile DSS2 are pinpoint. On the other hand, I use to lose star colours specially in the brightest ones , when postprocessing and stretching histogram. Maybe some day I will learn how to fix all these errors …

Polaris A & Polaris B

Polaris has a close neighbor at 18 arcseconds that can be spotted easily through a telescope.

This is a 15 seconds exposure through a Meade Lightbridge 16-inch, a Dobson with no tracking, but fortunately Polaris moves very slowly through its small circumpolar path, due to its proximity to north pole in the sky. The camera used was a Canon EOS 450d, also known as Rebel XTi. The method employed was an eyepiece projection using a 14mm Meade Series 5000.

Light Pollution

Light pollution in suburban skies makes nearly impossible astrophotography. Nevertheless, there exists some computer techniques to make it possible. I have used a dark frame to catch the exact pattern of the light pollution in the photographed area. The way to accomplish this is not difficult. Shooting in continuous mode the DSLR camera facing the zenith in my home window, and forcing every frame to last 15 seconds I got a sequence of subframes to be processed afterward.

To get the dark frame I do some image arithmetic with Paint Shop Pro 9: I choose 3 or 4 distant subframes and compute them using “darkest” option. This way, stars become to fade until disappearing.

With Paint Shop Pro 9 and batch processor I apply a barrel lens distortion of 17 (empirical value to correct a 18mm focal lens like Canon’s) to every subframe and also to the dark frame.

Once got the dark frame DeepSkyStacker is needed to stack the single subframes and substract the dark frame. The sideral drift of the field is automatically compensated with the intelligent algorithm that DeepSkyStacker provides.

The resulting image is surprising taking into account this is an urban sky.

Dobsonian Astrophotography

Question: I have a 14 inch dob and interested in taking photos with it. Do I really need tracking?

I have a Dobsonian Meade Lightbridge 16-inch and I am also trying to do astrophotography with it. This is a challenge. The Moon is the easiest target for a Dob. Tracking is not compulsory to take good images of the Moon. Next target may be planets. Here it is my last image of Saturn through my Dob:

Saturn improved

Next target would be bright stars and clusters. And the most difficult target of all is deep-sky astrophotography. With no tracking system you have to use some tricks to get deep sky images. I am using shift-and-add technique with moderate results.

My focuser does not let me to use my DSLR camera at prime focus, so I am using afocal method through low power eyepieces. You don’t have to spend much money to do this kind of photographic experiments. Patience and effort sometimes give more satisfaction that a lot of money expended in sophisticated equipment.

Background substraction

Astrophotos taken in light polluted skies use to show a noisy gray background that should be avoided mainly for aesthetic reasons, and also to gain contrast in deep-sky objects. Using some image software like Paintshop Pro or Photoshop it is simple to correct the image in 4 steps:

1.- Make a copy of the image.

2.- Level the copy from zero to the highest background noise value. This way bright stars will appear as dim as background.

3.- Gaussian Blur the copy.

4.- Substract the copy to the original picture. You may add a small offset to the substraction if the background removal is very hard.

Here is an example with Orion constellation: