Date: 25 December 2006 U.T.
Time: 4:50 - 5:18 & 5:45 - 6:05 U.T.
Telescope: 30cm Newtonian
Magnification: 38x
Seeing: Good
NELM: 6.0
Temperature: +12 F (-11 C)
Prior to getting down to business:
The telescope was set up shortly after sunset, allowing Andrew a peek at the crescent moon at 80x. Later, after moonset, Ann and Andrew got good views of the Great Orion Nebula at 80x. Andrew stuck around long enough to view a few additional objects.
Starting at 4:50 U.T. I once again worked on sketching the Andromeda Galaxy (M 31). At 5:45 U.T., after having taken a break, I revisited the Pleiades Star Cluster (M 45) for yet another sketch of the associated nebulosity. As it turned out, this wasn't a very good night for these tasks; but I did the best I could under the circumstances. The difference between a 6.5 and 6.0 magnitude sky is quite noticeable when one is attempting to study faint objects or features. Nevertheless, I feel that I now have enough raw material to attempt new and improved paintings of both celestial showpieces.
Telescope Care:
By the end of the session the porch, grass, telescope, etc. had acquired a coating of frost. Yet, due to preventive procedures, I was able to avoid any frost or dew formation on the telescope mirrors -- while outdoors as well as after returning indoors.
Many years ago, after bringing in a very cold telescope, I had learned an important lesson. The telescope had been outside for several hours when the air temperature (excluding any windchill) was -20 F (-29 C). After bringing the frigid telescope indoors, the cold glass and metal attracted moisture like magnets. Before long the telescope had acquired a thick coating of ice (remember, this was after the scope had been brought inside). After more time had passed and the telescope had warmed sufficiently, chunks of ice broke off, fell to the floor, and gradually liquified. Of course, water spots persisted on the optical surfaces after the scope had completely dried.
Now I always cover all optical surfaces, tube openings, etc. before bringing a cold telescope indoors. When practical, either the entire telescope or key components are also boxed prior to bringing them indoors. Despite several recent nights of use at below freezing temperatures, the mirrors of the 30cm telescope have never had any form of condensed moisture on them. Consequently, the optics remain pristine -- no 'water spots'.
25 December 2006
22 December 2006
Andromeda Revisited
Date: 22 December 2006 U.T.
Time: 2:55 - 4:06 U.T.
Telescope: 13cm refractor
Magnification: 21x
Seeing: Good
NELM: ~6.0
Temperature: +19 F (-7 C)
The sky was partly cloudy at the beginning of this session and almost totally cloud covered by the end. Once again I worked on the Andromeda Galaxy and surrounding star field. This time I was able to see the entire visible portion of the galaxy within the refractor's wide, 3.1 degree FOV.
Most of the session was devoted to marking the numerous field stars. Unlike the sketch that was uploaded with my previous posting, this time all visible stars were recorded excepting only those that I would have had to 'work at' to see.
As for the Galaxy itself, brightness variations were better recorded and dust lanes were less obvious (not that they were all that obvious earlier).
I've yet to transform the 'at the telescope' sketch into a sketch suitable for uploading. I want to try one more M31 session with the refractor in an effort to ferret out any 'hidden' details that might remain to be seen at 21x. I hope to eventually make a painting that more accurately shows the visual appearance of the three galaxies and surrounding star field. If I'm successful, this painting will be the beginning of yet another new project. If I'm not successful, I'll just have to keep on trying until I am!
Time: 2:55 - 4:06 U.T.
Telescope: 13cm refractor
Magnification: 21x
Seeing: Good
NELM: ~6.0
Temperature: +19 F (-7 C)
The sky was partly cloudy at the beginning of this session and almost totally cloud covered by the end. Once again I worked on the Andromeda Galaxy and surrounding star field. This time I was able to see the entire visible portion of the galaxy within the refractor's wide, 3.1 degree FOV.
Most of the session was devoted to marking the numerous field stars. Unlike the sketch that was uploaded with my previous posting, this time all visible stars were recorded excepting only those that I would have had to 'work at' to see.
As for the Galaxy itself, brightness variations were better recorded and dust lanes were less obvious (not that they were all that obvious earlier).
I've yet to transform the 'at the telescope' sketch into a sketch suitable for uploading. I want to try one more M31 session with the refractor in an effort to ferret out any 'hidden' details that might remain to be seen at 21x. I hope to eventually make a painting that more accurately shows the visual appearance of the three galaxies and surrounding star field. If I'm successful, this painting will be the beginning of yet another new project. If I'm not successful, I'll just have to keep on trying until I am!
19 December 2006
Andromeda Galaxy
Date: 19 December 2006
Time: 5:25 - 5:50 U.T.
Telescope: 30cm Netwonian
Magnification: 38x
Seeing: Fair
NELM: 6.3
Temperature: +13 F (-11 C)
The above sketch shows the Great Andromeda Galaxy (M31) and two of its satellite galaxies, M32 above and M110 below. South is up. West is to the left. The circular field is 1.7 degrees in diameter. M31's coordinates are: RA 0hr 43', Dec +41 16'. Only a few of the field stars are shown in this sketch. 38x is my lowest magnification and 1.7 degrees is my widest FOV for the 30cm Newtonian. In order to see M31 in its entirety a smaller telescope (with a wider FOV), or binoculars is necessary. Notice the two dust lanes below the great galaxy's nucleus. Those lanes (and others) are easier to see at higher magnifications.
Time: 5:25 - 5:50 U.T.
Telescope: 30cm Netwonian
Magnification: 38x
Seeing: Fair
NELM: 6.3
Temperature: +13 F (-11 C)
The above sketch shows the Great Andromeda Galaxy (M31) and two of its satellite galaxies, M32 above and M110 below. South is up. West is to the left. The circular field is 1.7 degrees in diameter. M31's coordinates are: RA 0hr 43', Dec +41 16'. Only a few of the field stars are shown in this sketch. 38x is my lowest magnification and 1.7 degrees is my widest FOV for the 30cm Newtonian. In order to see M31 in its entirety a smaller telescope (with a wider FOV), or binoculars is necessary. Notice the two dust lanes below the great galaxy's nucleus. Those lanes (and others) are easier to see at higher magnifications.
Pleiades Star Cluster
Date: 19 December 2006 U.T.
Time: 3:04 - 3:51 U.T.
Telescope: 30cm Newtonian
Magnification: 38x
Seeing: Fair
NELM: 6.3
Temperature: +15 F (-9 C)
The above sketch shows the Pleaides Star Cluster, also known as M45 and The Seven Sisters. It's located at RA 3hr 47', Dec +24 07'. South is up. West is to the left. The circular field is 1.7 degrees in diameter. Note the nebulosity visible around a few of the brighter stars.
Time: 3:04 - 3:51 U.T.
Telescope: 30cm Newtonian
Magnification: 38x
Seeing: Fair
NELM: 6.3
Temperature: +15 F (-9 C)
The above sketch shows the Pleaides Star Cluster, also known as M45 and The Seven Sisters. It's located at RA 3hr 47', Dec +24 07'. South is up. West is to the left. The circular field is 1.7 degrees in diameter. Note the nebulosity visible around a few of the brighter stars.
18 December 2006
The Crab Nebula
Date: 18 December 2006 U.T.
Time: 5:20 U.T.
Telescope: 30cm Newtonian
Magnification: 155x
Seeing: Bad
NELM: 6.2
Temperature: +12 F (-11 C)
The above sketch shows the Crab Nebula, also known as M1 and NGC 1952. South is up. West is to the left. The sketched field is about eleven minutes of arc wide. The Crab is located at: RA 5hr 34.5', Dec. +22 01'. The Crab is a supernova remnant - the remains of an exploded star. It's visible with small binoculars from a dark site as a tiny, faint, smudge on the background sky.
Later on this night an observation of Saturn was attempted; but seeing conditions were too poor to allow the use of reasonable magnifications.
In response to Bill Hudson's question: I use pencil on white paper at the telescope. Later I make use of the telescope sketch to make a better quality, scannable sketch. I'm still experimenting to some degree. Sometimes for the scannable image I've used pencil alone, sometimes I've also use pen. I've been posting negatives of those images to the blog. IIRC, my website only has 'positives'. There's a link to the website on my 'profile'. Thanks for your question!
15 December 2006
Aurora Borealis
Date: 15 December 2006 U.T.
Time: 2:00 - 4:15 U.T.
Transparency: Mostly Clear to Mostly Cloudy
Latitude: 45.5 North
Location: Northwestern U.S.
Shortly before 2:00 U.T. I stepped out the south door to check sky conditions. (The sky had been cloudy earlier.) I was greeted by a mostly clear sky and a strong glow in the east. A look out the north door verified my suspicion: An aurora was in progress.
A large, bright, pale green auroral glow extended from within Orion in the east-southeast through Auriga, Cassiopeia, etc. all the way to Cygnus in the northwest (basically following the Milky Way) and all points northward. The display consisted of an amorphous glow with a few, small, pulsating patches -- mostly in the northeast.
At roughly 15 minute intervals I checked on the auroral activity. Throughout my auroral watch the large glow described above remained visible. This glow had the appearance of a huge, broad dome. Its high point, in the direction of magnetic north, was within a few degrees of the zenith.
Around 3:15 U.T. a pulsating arc would occasionally appear and disappear in a matter of seconds, passing above Polaris.
By 3:45 U.T. the thin clouds were beginning to grow thicker everywhere. A short, bright, rayed-arc was visible near the horizon in the direction of magnetic north (a few degrees east of true north). This arc, in addition to the huge glow mentioned earlier, remained visible until the clouds became nearly opaque at 4:15 U.T.
Time: 2:00 - 4:15 U.T.
Transparency: Mostly Clear to Mostly Cloudy
Latitude: 45.5 North
Location: Northwestern U.S.
Shortly before 2:00 U.T. I stepped out the south door to check sky conditions. (The sky had been cloudy earlier.) I was greeted by a mostly clear sky and a strong glow in the east. A look out the north door verified my suspicion: An aurora was in progress.
A large, bright, pale green auroral glow extended from within Orion in the east-southeast through Auriga, Cassiopeia, etc. all the way to Cygnus in the northwest (basically following the Milky Way) and all points northward. The display consisted of an amorphous glow with a few, small, pulsating patches -- mostly in the northeast.
At roughly 15 minute intervals I checked on the auroral activity. Throughout my auroral watch the large glow described above remained visible. This glow had the appearance of a huge, broad dome. Its high point, in the direction of magnetic north, was within a few degrees of the zenith.
Around 3:15 U.T. a pulsating arc would occasionally appear and disappear in a matter of seconds, passing above Polaris.
By 3:45 U.T. the thin clouds were beginning to grow thicker everywhere. A short, bright, rayed-arc was visible near the horizon in the direction of magnetic north (a few degrees east of true north). This arc, in addition to the huge glow mentioned earlier, remained visible until the clouds became nearly opaque at 4:15 U.T.
14 December 2006
Geminid Meteor Shower
Date: 14 December 2006 U.T.
Time: 6:12 - 7:08 and 9:05 - 9:21 U.T.
NELM: 6.5 and worse (see below)
Temperature: +40 F (+4 C)
Wind: Moderate
After completing my observation of NGC 2174 (my previous posting) I spent some time looking for Geminid meteors with the unaided-eye.
From 6:12 until 7:08 U.T. I saw 102 Geminids and at least half a dozen sporadic (non-Geminid) meteors. Most of the Geminids were quite bright -- first or second magnitude. Some left trains that remained visible briefly after their parent meteors had vanished. The Geminids were relatively slow moving compared to most meteors. Their color seemed to be yellow-white. The sky remained mostly clear with a NELM of 6.5. An auroral glow reduced the limiting magnitude in selective directions; but the winter Milky Way remained visible from my northwest horizon to my southeast horizon. I took a break at 7:08 U.T.
From 9:05 until 9:21 U.T. I saw 26 more Geminids. The sky was covered with clouds, mostly thin; but in some places they were nearly opaque. The crescent moon was low in the east-southeast. The light from the brighter Geminids penetrated the clouds with ease.
Time: 6:12 - 7:08 and 9:05 - 9:21 U.T.
NELM: 6.5 and worse (see below)
Temperature: +40 F (+4 C)
Wind: Moderate
After completing my observation of NGC 2174 (my previous posting) I spent some time looking for Geminid meteors with the unaided-eye.
From 6:12 until 7:08 U.T. I saw 102 Geminids and at least half a dozen sporadic (non-Geminid) meteors. Most of the Geminids were quite bright -- first or second magnitude. Some left trains that remained visible briefly after their parent meteors had vanished. The Geminids were relatively slow moving compared to most meteors. Their color seemed to be yellow-white. The sky remained mostly clear with a NELM of 6.5. An auroral glow reduced the limiting magnitude in selective directions; but the winter Milky Way remained visible from my northwest horizon to my southeast horizon. I took a break at 7:08 U.T.
From 9:05 until 9:21 U.T. I saw 26 more Geminids. The sky was covered with clouds, mostly thin; but in some places they were nearly opaque. The crescent moon was low in the east-southeast. The light from the brighter Geminids penetrated the clouds with ease.
NGC 2174
Object: NGC 2174
Date: 14 December 2006 U.T.
Time: 5:45 - 6:00 U.T.
Binoculars: 25x100 tripod-mounted
Seeing: Good
NELM: 6.0 or better
Temperature: +40 F (+4 C)
Wind: Moderate
The above sketch is a close-up of the binocular view of NGC 2174 (RA 06hr 09.7', Dec. +20 30'). North is up. West is to the right. The sketch covers an area approximately 30 minutes of arc across. This nebula appeared considerably fainter in the binoculars than shown in the sketch. It was difficult to ascertain its edges. A bay-like structure was visible in the southwest. Fainter nebulosity extended southward from the brighter region.
Date: 14 December 2006 U.T.
Time: 5:45 - 6:00 U.T.
Binoculars: 25x100 tripod-mounted
Seeing: Good
NELM: 6.0 or better
Temperature: +40 F (+4 C)
Wind: Moderate
The above sketch is a close-up of the binocular view of NGC 2174 (RA 06hr 09.7', Dec. +20 30'). North is up. West is to the right. The sketch covers an area approximately 30 minutes of arc across. This nebula appeared considerably fainter in the binoculars than shown in the sketch. It was difficult to ascertain its edges. A bay-like structure was visible in the southwest. Fainter nebulosity extended southward from the brighter region.
12 December 2006
NGC 247 and More
Objects: NGCs 247, 216, and 210
Date: 12 December 2006 U.T.
Time: 2:46, 3:08, and 4:05 U.T. respectively
NELM: greater than or equal to 6.5
Seeing: Good (for magnifications used)
Telescope: 30cm Newtonian
Magnifications: 56x, 81x, and 98x
Site Latitude: 45.5 North
Temperature: +22 F. (-6 C)
NGC 247: (RA 00hr 47.1', Dec. -20 46') Above is a sketch of NGC 247 with south up and preceding (west) to the left. The sketched area is approximately 31' wide. This fairly bright galaxy appeared better on this night at 56x. NGC 247 appeared large and elongated with a very gradually, little brighter, elongated, central region. An easily visible star punctuated the galaxy's southern end. The north end of NGC 247 appeared to be a little wider and more indistinct (fainter) than the galaxy's south end. Twenty-one point five degrees south declination is near the southern limit for the 30cm telescope. This is the same limit as one series of charts in the Millennium Star Atlas. The south wall of my open-air observatory prevents an unobstructed view much closer to my southern horizon. Consequently, current plans call for observing objects (with the 30cm telescope) at or north of 21.5 degrees S. Dec.
NGC 216: (RA 00hr 41.4', Dec. -21 03') This galaxy was missed at 56x; but at 98x it looked like a small, faint stain on the background sky.
NGC 210: (RA 00hr 40.6', Dec. -13 52') At 98x NGC 210 was small and bright with a much brighter center. A bright star was just west of this galaxy.
Other Notes: An aurora fooled me into thinking the moon was about to rise (most of my low northern sky was blocked from view as seen from my observing site). Frost found its way to most exposed surfaces fairly quickly on this night. I took a quick look at the Great Orion Nebula. It was an awesome sight! Following up on a posting I read on sci.astro.amateur, I used 8x42 and 20x80 binoculars to checkout NGC 2174 in the northeast corner of Orion. This patch of nebulosity is indeed visible with small binoculars. I failed to take time out for a high magnification view of Polaris for an accurate determination of seeing conditions; but stars remained reasonably sharp at all magnifications used on this night.
Date: 12 December 2006 U.T.
Time: 2:46, 3:08, and 4:05 U.T. respectively
NELM: greater than or equal to 6.5
Seeing: Good (for magnifications used)
Telescope: 30cm Newtonian
Magnifications: 56x, 81x, and 98x
Site Latitude: 45.5 North
Temperature: +22 F. (-6 C)
NGC 247: (RA 00hr 47.1', Dec. -20 46') Above is a sketch of NGC 247 with south up and preceding (west) to the left. The sketched area is approximately 31' wide. This fairly bright galaxy appeared better on this night at 56x. NGC 247 appeared large and elongated with a very gradually, little brighter, elongated, central region. An easily visible star punctuated the galaxy's southern end. The north end of NGC 247 appeared to be a little wider and more indistinct (fainter) than the galaxy's south end. Twenty-one point five degrees south declination is near the southern limit for the 30cm telescope. This is the same limit as one series of charts in the Millennium Star Atlas. The south wall of my open-air observatory prevents an unobstructed view much closer to my southern horizon. Consequently, current plans call for observing objects (with the 30cm telescope) at or north of 21.5 degrees S. Dec.
NGC 216: (RA 00hr 41.4', Dec. -21 03') This galaxy was missed at 56x; but at 98x it looked like a small, faint stain on the background sky.
NGC 210: (RA 00hr 40.6', Dec. -13 52') At 98x NGC 210 was small and bright with a much brighter center. A bright star was just west of this galaxy.
Other Notes: An aurora fooled me into thinking the moon was about to rise (most of my low northern sky was blocked from view as seen from my observing site). Frost found its way to most exposed surfaces fairly quickly on this night. I took a quick look at the Great Orion Nebula. It was an awesome sight! Following up on a posting I read on sci.astro.amateur, I used 8x42 and 20x80 binoculars to checkout NGC 2174 in the northeast corner of Orion. This patch of nebulosity is indeed visible with small binoculars. I failed to take time out for a high magnification view of Polaris for an accurate determination of seeing conditions; but stars remained reasonably sharp at all magnifications used on this night.
10 December 2006
SUNSPOT OBSERVATION
Object: SUNSPOT
Date: 10 December 2006 U.T.
Time: 18:47 - 19:00 U.T.
Seeing: Fair
Telescope: 102mm SCT
Magnification: 72x
Filter(s): Baader, White-Light, Objective Solar Filter
Seeing conditions improved enough from earlier this morning to allow
a sketch to be made of the large sunspot that was mentioned in my previous post. It's worth pointing out that this sunspot's umbra had a boundary consisting of a multitude of "spikes" sticking out radially into the spot's penumbra -- as shown in the sketch. North is up. Preceding (west) is to the left.
Date: 10 December 2006 U.T.
Time: 18:47 - 19:00 U.T.
Seeing: Fair
Telescope: 102mm SCT
Magnification: 72x
Filter(s): Baader, White-Light, Objective Solar Filter
Seeing conditions improved enough from earlier this morning to allow
a sketch to be made of the large sunspot that was mentioned in my previous post. It's worth pointing out that this sunspot's umbra had a boundary consisting of a multitude of "spikes" sticking out radially into the spot's penumbra -- as shown in the sketch. North is up. Preceding (west) is to the left.
PLANETS IN MORNING SKY
Date: 10 December 2006 U.T.
Time: 13:30 - 14:10 U.T.
Telescope: 80mm refractor
Magnification(s): 17x, 22x
Binoculars: 8x42
Temperature: +17 F (-8 C)
Saturn was spotted with the unaided-eye close to the waning gibbous Moon high in the morning sky.
The morning's tight grouping of Mercury, Jupiter, and Mars was spotted between pine trees low in the southeastern sky using 8x42 binoculars. Mercury was very close to and above Jupiter. The star Beta Scorpii was nearby and above Mercury. Mars was a bit more distant, off to one side. Only Mercury and Jupiter were obvious to the unaided-eye in the brightening twilight. The star and all three planets were close enough to one another to fit within the same FOV with the telescope as well as with the binoculars.
After sunrise I took a quick look at the Sun using the refractor at 22x. An objective solar filter was in place over the front of the telescope for safe viewing. A single, large sunspot was immediately obvious. It was flanked on either side by a smaller spot. Seeing conditions were too poor to justify increasing magnification or making a sketch. The main spot was large enough to be visible to the unaided-eye (protected by looking through a Sun filter).
Time: 13:30 - 14:10 U.T.
Telescope: 80mm refractor
Magnification(s): 17x, 22x
Binoculars: 8x42
Temperature: +17 F (-8 C)
Saturn was spotted with the unaided-eye close to the waning gibbous Moon high in the morning sky.
The morning's tight grouping of Mercury, Jupiter, and Mars was spotted between pine trees low in the southeastern sky using 8x42 binoculars. Mercury was very close to and above Jupiter. The star Beta Scorpii was nearby and above Mercury. Mars was a bit more distant, off to one side. Only Mercury and Jupiter were obvious to the unaided-eye in the brightening twilight. The star and all three planets were close enough to one another to fit within the same FOV with the telescope as well as with the binoculars.
After sunrise I took a quick look at the Sun using the refractor at 22x. An objective solar filter was in place over the front of the telescope for safe viewing. A single, large sunspot was immediately obvious. It was flanked on either side by a smaller spot. Seeing conditions were too poor to justify increasing magnification or making a sketch. The main spot was large enough to be visible to the unaided-eye (protected by looking through a Sun filter).
06 December 2006
TERMINOLOGY
Aperture: This is the diameter of the telescope's objective ( front lens, corrector or primary mirror depending on the type of telescope). A telescope's aperture determines its light-gathering power and resolution limit.
Binocular Terminology: Binocular specifications are given by specifying the magnification and aperture (in millimeters) separated by an "x". For example, 20x80 binoculars have a magnification of 20x and front lenses (objectives) that are 80 millimeters in diameter.
Date: Dates within postings are provided in Universal Time (corresponding to the date in Greenwich, England at the time of the observation) and are followed by "U.T."
FOV: This is an abbreviated term for "Field Of View". It's used to communicate the diameter of the area of sky visible when looking through an optical instrument. It may be specified in degrees and fractions of a degree, as in 3.1 degrees (three and one-tenth degrees); or in minutes and/or seconds of arc as in 32' 15" (thirty-two minutes fifteen seconds). There are 60 minutes of arc in one degree, and 60 seconds of arc in one minute of arc.
Magnification: This is how many times larger an object appears in a telescope than it would appear to the unaided-eye. An "x" appears after the number. For a magnification of fifty-six I would type: 56x. A telescope's magnification is easily changed by changing to a different eyepiece.
NELM: I use this term as an abbreviation for "Naked-Eye Limiting Magnitude". It's the magnitude (brightness) of the faintest star visible to the unaided-eye at the zenith (directly overhead). A larger number signifies a fainter star. NELM is used as a measure of sky darkness. In general I make use of a group of stars of known brightness in the vicinity of Polaris, the North Star. A minor adjustment is made to arrive at the value for the zenith.
Newtonian: A telescope type invented by Sir Isaac Newton that utilizes a parabolic mirror at the back end of the telescope tube to collect and concentrate light. A small, flat, diagonal mirror in the center of the front of the tube redirects the light to the side of the tube where the eyepiece is located. A Newtonian is a type of reflecting telescope.
Refractor: A telescope that utilizes a front, objective lens (or lenses) to collect and concentrate light is a refractor. A "spyglass" is a refractor. Achromats and apochromats are types of refractors.
SCT: "Schmidt Cassegrain Telescope" -- One of several types of telescopes that utilize a combination of mirrors and lenses to collect and concentrate light. The secondary mirror of an SCT is in the center of the front lens (corrector plate).
Seeing: This is a measure of atmospheric steadiness. In this blog I'll use the terms: Excellent, Good, Fair, Poor, and Bad. When appropriate I'll use the appearance of the highly magnified image of a star to determine night-time seeing conditions. This scale (not fully explained here) is dependent upon a telescope's aperture. For example, a night of Good seeing with a small telescope might be a night of equal or worse seeing for a larger telescope.
Telescope: When describing which telescope I used, I first provide the telescope's Aperture (see above) followed by the type of telescope (Newtonian, Refractor, SCT, etc.).
Time: All times, unless otherwise specified, will be Universal Time (basically Greenwich Mean Time). I'll try to add a "U.T." as a reminder, as in 23:45 U.T.
Binocular Terminology: Binocular specifications are given by specifying the magnification and aperture (in millimeters) separated by an "x". For example, 20x80 binoculars have a magnification of 20x and front lenses (objectives) that are 80 millimeters in diameter.
Date: Dates within postings are provided in Universal Time (corresponding to the date in Greenwich, England at the time of the observation) and are followed by "U.T."
FOV: This is an abbreviated term for "Field Of View". It's used to communicate the diameter of the area of sky visible when looking through an optical instrument. It may be specified in degrees and fractions of a degree, as in 3.1 degrees (three and one-tenth degrees); or in minutes and/or seconds of arc as in 32' 15" (thirty-two minutes fifteen seconds). There are 60 minutes of arc in one degree, and 60 seconds of arc in one minute of arc.
Magnification: This is how many times larger an object appears in a telescope than it would appear to the unaided-eye. An "x" appears after the number. For a magnification of fifty-six I would type: 56x. A telescope's magnification is easily changed by changing to a different eyepiece.
NELM: I use this term as an abbreviation for "Naked-Eye Limiting Magnitude". It's the magnitude (brightness) of the faintest star visible to the unaided-eye at the zenith (directly overhead). A larger number signifies a fainter star. NELM is used as a measure of sky darkness. In general I make use of a group of stars of known brightness in the vicinity of Polaris, the North Star. A minor adjustment is made to arrive at the value for the zenith.
Newtonian: A telescope type invented by Sir Isaac Newton that utilizes a parabolic mirror at the back end of the telescope tube to collect and concentrate light. A small, flat, diagonal mirror in the center of the front of the tube redirects the light to the side of the tube where the eyepiece is located. A Newtonian is a type of reflecting telescope.
Refractor: A telescope that utilizes a front, objective lens (or lenses) to collect and concentrate light is a refractor. A "spyglass" is a refractor. Achromats and apochromats are types of refractors.
SCT: "Schmidt Cassegrain Telescope" -- One of several types of telescopes that utilize a combination of mirrors and lenses to collect and concentrate light. The secondary mirror of an SCT is in the center of the front lens (corrector plate).
Seeing: This is a measure of atmospheric steadiness. In this blog I'll use the terms: Excellent, Good, Fair, Poor, and Bad. When appropriate I'll use the appearance of the highly magnified image of a star to determine night-time seeing conditions. This scale (not fully explained here) is dependent upon a telescope's aperture. For example, a night of Good seeing with a small telescope might be a night of equal or worse seeing for a larger telescope.
Telescope: When describing which telescope I used, I first provide the telescope's Aperture (see above) followed by the type of telescope (Newtonian, Refractor, SCT, etc.).
Time: All times, unless otherwise specified, will be Universal Time (basically Greenwich Mean Time). I'll try to add a "U.T." as a reminder, as in 23:45 U.T.
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