Moon

A combination of 4 of the best images, automatically selected using CCDOps. Partially overexposed. Click on the image to see the full version.

2003-10-16:

The Bubble Nebula NGC 7635

My first true LRGB image.

2003-10-11:

Uranus, Umbriel, Oberon and Titania

The following image of Uranus and three of its moons was taken on the night of October 11, 2003 in front of my apartement in San Jose, CA. In this image, North is down, and East is left. Uranus has a computed magnitude of 5.75, and an apparent angular diameter of 3.62 arc seconds. Known stars of the GSC catalog are marked with their GSC magnitudes (decimal dot before last digit removed).

Using AIP4WIN (star aperture 4, inner sky annulus 6, outer sky annulus 10) and the magnitude 11.2 GSC 5805:40 star at the top left of the image (chosen because it is the faintest one mentioned in the Tycho catalog, and therefore assumed to have a more reliable magnitude: Vt=11.265), it was determined that the three moons had the following magnitude:

Object	Magnitude
Umbriel	-
Oberon	13.9
Titania	13.8

Umbriel is too close to Uranus in the image for an accurate magnitude determination. These values are close to the values calculated using the NASA Ephiremide generator:

Object	Magnitude
Umbriel	15.0
Oberon	14.2
Titania	14.0

The difference is caused by the fact that the image was obtained through a RGB red filter, while the comparisment star magnitude is a V magnitude. Another reason is that the difference in brightness between the moons and the comparisent star is almost 3 magnitudes, which reduces the accuracy.

2003-10-10: 8 minute exposure (50x10s). Camera cooled to -20°C.

Using the known positions of the GSC stars, it was determined that the center of the image is located at 22h 06m 18.67s -12d 29m 56.55s. Similary, the locations of Uranus and its moons were determined as:

Object	RA             Dec
Uranus	22h 06m 17.00s -12d 29m 39.79s
Umbriel	22h 06m 16.79s -12d 28m 20.68s*
Oberon	22h 06m 17.10s -12d 29m 06.70s
Titania	22h 06m 16.24s -12d 29m 19.85s

*The position of Umbriel is only an approximation, as it could not be determined accurately.
The apparent angular distance between the objects in arc seconds and their position angle is:

Object   Uranus     Umbriel Oberon    Titania
Uranus   -          ?       33.1 2.6  22.9 330.8
Umbriel  ?          -       ?         ?
Oberon   33.1 357.4 ?       -         18.2 316.1
Titania  22.9 29.2  ?       18.2 43.9 -

Miranda & Ariel are too close to Uranus (8 arc seconds from center) and could not be imaged. The star left under of Uranus can be found in the USNO-SA2.0 database as a mag 15.3 star. The object right of Uranus doesn't exist in this database (in other words, I do not know yet what it is).

Galaxy NGC 891

A clear improvement of my first attempt, 9 months earlier on my third imaging session.

2003-10-10: 15 minute exposure (3x300s). Camera cooled to -20°C.

Planetary Nebula NGC 246

This planetary nebula was discovered in 1785 by William Herschel. It is of relatively low surface brightness. As can be seen in this image, the central star of this nebula is actually two stars close in angular separation. The central star is of magnitude 11.9. Its companion at 3.8 arcseconds distance is of magnitude 14.

The planetary nebula has an apparent diameter of 4 arcminutes. Compare this to the moon, which has an apparent diameter of 30 arcminutes. Several stars are superimposed on this nebula.

2003-10-10: 30 minute exposure through a red, green and blue filter each (3x3x600s). Camera cooled to -20°C.

Galaxy M77 (NGC 1068)

M77 is a magnitude 9.6 (8.9?), type Sb spiral galaxy in the constellation Cetus. It is over 170,000 light years across (bright part measuring about 120,000 light years,) and over 49 million light years away (60000 (kly)?).

It is the nearest and brightest example of a type II Seyfert galaxy, showing broad and strong emission lines due to high velocity gas in the galaxy's inner regions. A strong radio source (probably a supermassive blackhole) known as Cetus A sits in the nucleus.

The foreground star to the left of M77 is the magnitude 10.81 HIP 12668, on a distance of 982.40 light years and spectral type G0. Using this image, I determined the angular separation between this star and the galaxy core is 88.1 arcseconds (PA 295°).

2003-10-10: 30 minute exposure through a red, green and blue filter each (3x3x600s). Camera cooled to -20°C.

Galaxy M31

Last night I did my first attempts to color imaging with my ST-7XE. This LRGB image depicts the central region of M31. The dust is clearly visible, but the coma in the source images made it impossible for me to properly line up the individual images.

2003-10-10: Camera cooled to -20°C.