Hi, I don't know if this has been posted before.
I am a newbie trying to help other newbies as well. I know very little about telescopes and I wanted to buy one to do astronomy and terrestrial viewing (not watching pretty girls along the streets hor), so I decided to do some research before getting a telescope. I came across this wonderful site that explains the fundamentals of a telescope. There are 31 pages of it, so enjoy!
http://science.howstuffworks.com/telescope.htm
In addition, these are some videos to go along to help you gain some telescope knowledge. Go to this guy's channel, he has more videos to show!
Some useful info for freshies
-
- Posts: 60
- Joined: Sat Nov 20, 2010 2:03 am
- Favourite scope: Celestron Tavelscope 70
- Location: Singapore
Some useful info for freshies
Last edited by Desmond_T on Wed Jul 03, 2013 6:12 pm, edited 1 time in total.
Clear skies~
-
- Posts: 376
- Joined: Fri May 17, 2013 2:50 am
- Favourite scope: maksutov
Re: Some useful info for freshies
A few links that I find useful.
http://www.stargazing.net/naa/scopemath.htm
Cloud satellite view of past 6 hours
http://www.accuweather.com/en/sg/national/satellite
Rain radar ... save URL as bookmark, refresh the page every few minutes for update
http://www.weather.gov.sg/wip/pp/rndops ... /rad70.gif
http://www.stargazing.net/naa/scopemath.htm
Cloud satellite view of past 6 hours
http://www.accuweather.com/en/sg/national/satellite
Rain radar ... save URL as bookmark, refresh the page every few minutes for update
http://www.weather.gov.sg/wip/pp/rndops ... /rad70.gif
-
- Posts: 60
- Joined: Sat Nov 20, 2010 2:03 am
- Favourite scope: Celestron Tavelscope 70
- Location: Singapore
Re: Some useful info for freshies
This is a good site to understand more about the cosmos and astronomy. Khan Academy is like a non-profit tutorial website that teaches Science, Maths, Economics and Humanities subjects. Very interesting concept of learning online. So, enjoy!
http://www.khanacademy.org/science/cosm ... -astronomy
http://www.khanacademy.org/science/cosm ... -astronomy
Clear skies~
Re: Some useful info for freshies
@Hardwarezone - Thanks for sharing links. I found them useful too.
@Desmond_T - Thanks for sharing the links. There are many wonderful astronomy/telescope related channels in YouTube. I think we are living in the golden age in terms of free astronomy info.
The howstuffworks article is a fantastic single online resource about telescopes, mounts, accessories and stargazing info. Very well written overall. But like all information we gather online, not everything mentioned is true or still applicable today.
A few examples from this article:
"no reflective coating for a mirror returns 100 percent of the light striking it -- the best coatings return 90 percent of incoming light."
This statement may be mis-interpreted as 90% is the maximum and may "scare" newcomers considering getting a reflector. Compared to the loss of light through modern refractors, 10% may seems to be a lot. Perhaps better phrasing is "more than 90%".
"The Pleiades has seven bright stars that can be seen with the naked eye; but when viewed in a small telescope like mine, many thousands jump out at you."
I think "many thousands" is an over-exaggeration for a small telescope. Perhaps only true under the best clear skies with the highest quality optics in a small telescope which most people don't have easy access to.
"If you wish to do astrophotography, an equatorial mount is necessary."
To a newcomer, mentioning astrophotography (AP) without further qualifying it and then mention eq mount is *necessary* may be misleading. There are different types of AP - e.g. lunar/planetary, starscapes with just camera + tripod, deep sky objects, afocal with handheld phone/camera over telescopes, ..etc. The computerised AZ goto mounts today can do *some* types of AP well enough.
Again, I would like to mention overall, I find the article very well written and accurate - especially the "Practical Considerations" and "FAQ" segment.
In conclusion, one should read/research as much as possible, from as many different sources/authors as possible and double check their understanding with active/experienced amateur/professional astronomers.
@Desmond_T - Thanks for sharing the links. There are many wonderful astronomy/telescope related channels in YouTube. I think we are living in the golden age in terms of free astronomy info.
The howstuffworks article is a fantastic single online resource about telescopes, mounts, accessories and stargazing info. Very well written overall. But like all information we gather online, not everything mentioned is true or still applicable today.
A few examples from this article:
"no reflective coating for a mirror returns 100 percent of the light striking it -- the best coatings return 90 percent of incoming light."
This statement may be mis-interpreted as 90% is the maximum and may "scare" newcomers considering getting a reflector. Compared to the loss of light through modern refractors, 10% may seems to be a lot. Perhaps better phrasing is "more than 90%".
"The Pleiades has seven bright stars that can be seen with the naked eye; but when viewed in a small telescope like mine, many thousands jump out at you."
I think "many thousands" is an over-exaggeration for a small telescope. Perhaps only true under the best clear skies with the highest quality optics in a small telescope which most people don't have easy access to.
"If you wish to do astrophotography, an equatorial mount is necessary."
To a newcomer, mentioning astrophotography (AP) without further qualifying it and then mention eq mount is *necessary* may be misleading. There are different types of AP - e.g. lunar/planetary, starscapes with just camera + tripod, deep sky objects, afocal with handheld phone/camera over telescopes, ..etc. The computerised AZ goto mounts today can do *some* types of AP well enough.
Again, I would like to mention overall, I find the article very well written and accurate - especially the "Practical Considerations" and "FAQ" segment.
In conclusion, one should read/research as much as possible, from as many different sources/authors as possible and double check their understanding with active/experienced amateur/professional astronomers.
Last edited by Gary on Thu Jul 04, 2013 2:45 am, edited 1 time in total.
http://www.astro.sg
email: gary[at]astro.sg
twitter: @astrosg
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.
email: gary[at]astro.sg
twitter: @astrosg
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.
-
- Posts: 60
- Joined: Sat Nov 20, 2010 2:03 am
- Favourite scope: Celestron Tavelscope 70
- Location: Singapore
Re: Some useful info for freshies
Hi Gary,
Thanks for clearing the sky on some mis-interpretations or misconceptions. I totally agree with you in that all online info should be scrutinised. Some things that work well for someone does not mean it will work well for others.
I have many questions yet to ask in this forum as I am still new to astronomy, should I or any newbie develop any misconceptions along the way, please feel free to correct that for us. It's my personal belief that building the right fundamentals is the right approach to science. Cheers, and clear skies!
Thanks for clearing the sky on some mis-interpretations or misconceptions. I totally agree with you in that all online info should be scrutinised. Some things that work well for someone does not mean it will work well for others.
I have many questions yet to ask in this forum as I am still new to astronomy, should I or any newbie develop any misconceptions along the way, please feel free to correct that for us. It's my personal belief that building the right fundamentals is the right approach to science. Cheers, and clear skies!
Clear skies~
-
- Posts: 95
- Joined: Tue May 21, 2013 11:28 pm
- Favourite scope: Nikon 85mm/f1.4 lens
Re: Some useful info for freshies
not sure whether this is useful, but at least it is more updated than our NEA satellite imagery. it's almost immediately update within 5mins after each hr!
http://www.jma.go.jp/en/gms/large.html? ... 0&mode=UTC
http://www.jma.go.jp/en/gms/large.html? ... 0&mode=UTC
-
- Posts: 60
- Joined: Sat Nov 20, 2010 2:03 am
- Favourite scope: Celestron Tavelscope 70
- Location: Singapore
Re: Some useful info for freshies
Hi, I found this guy's YouTube channel to be very fascinating. He is a lecturer who teaches astronomy and he has like a semister's worth of videos on his channel! Here are some of the videos, you can go to his channel to view all of them! Cheers.
Clear skies~
-
- Posts: 60
- Joined: Sat Nov 20, 2010 2:03 am
- Favourite scope: Celestron Tavelscope 70
- Location: Singapore
Re: Some useful info for freshies
Useful Formulas for Amateur Astronomers
Magnification of a Telescope
The most commonly used formula in amateur astronomy is used to calculate the magnification of a telescope:
magnification = focal length of telescope / focal length of eyepiece
Example: using a 10mm eyepiece in a telescope with a focal length of 1000mm results in a magnification of 100x (1000 / 10 = 100).
Maximum Magnification of a Telescope
Since we can simply use different eyepieces to reach different magnification, the temptation is to "pump-up" the power as high as possible. In theory and practice, a telescope with excellent optics is limited to a magnification of about 2 times the aperture (diameter of main object) measured in millimeters. Example: an 80mm refractor is limited to a maximum magnification of about 160x (80 x 2 = 160). Multiply inches by 25.4 to convert to millimeters.
Focal Ratio of a Telescope
The focal ratio of a telescope is mostly used when considering exposure time for astrophotography, but it is also a general characteristic of the telescope that can be useful in other discussions.
focal ratio = focal length of telescope / aperture of telescope
The result is written as f/focal ratio. Example: an 80mm telescope with an 800mm focal length has a focal ratio of f/10 (800 / 80 = 10 - note that both measurements must use the same unit, in this case mm).
Exit Pupil
The exit pupil of an instrument is the cylinder of light leaving the eyepiece. If the exit pupil is larger than the diameter of the fully opened (dark-adapted) pupil of your eye, some of the light will be wasted. Younger eyes typically have a maximum pupil of about 7mm; older eyes may be limited to 5 or 6mm. Various focal lengths and magnifications result in differing exit pupils.
exit pupil for binoculars = aperture of binocular in mm / magnification of binocular
Example: 10x50 binoculars have an aperture of 50 (the second number) and a magnification of 10 (the first number). The exit pupil of these binoculars would be 5mm (50 / 10 = 5).
exit pupil for telescope = focal length of eyepiece / focal ratio of telescope
Actually just a mathematical rearrangement of the formula given for a pair of binoculars, but this formula turns out to be much easier to work with. Example: using a 25mm eyepiece in a telescope with a focal ratio of f/10 results in an exit pupil of 2.5mm (25 / 10 = 2.5).
True Field of View
The true field of view (TFOV) of an instrument is a measurement of the actual field of view seen through the eyepiece. For example, the field of view might show about 1 degree of the sky at a time. A wider field of view is desirable for extended objects such as large nebula and open clusters. Calculation of the TFOV requires the apparent field of view (AFOV) of the eyepiece in use. This is a statistic available from the eyepiece manufacturer, but it is useful to note that most Plossls have an AFOV of about 50 degrees.
TFOV = AFOV of eyepiece / magnification given by eyepiece
Example: a 10mm Plossl with an AFOV of 50 degrees is used in a telescope of 1000mm focal length. The magnification given by this eyepiece is 100x (1000 / 10) so the TFOV is a half degree (50 / 100 = 0.5).
Resolving Limit
The resolving limit of an instrument is an expression of the smallest detail that can be detected by the instrument. The unit of measure is arcseconds (1/3600th of a degree) and a common test is detecting separation in the components in a very close double star. There are two commonly used calculations:
Rayleigh Limit = 5.5 / aperture of telescope in inches
Dawes Limit = 4.56 / aperture of telescope in inches
Example: the Rayleigh Limit for a telescope with a 6 inch aperture is approximately 0.9 arcseconds (5.5 / 6 = 0.92). To convert an aperture given in millimeters (mm) to inches, simply divide the millimeters by 25.4; for example, an 80mm aperture is 3.15 inches.
Light Gathering Power
This is not really an absolute measurement but rather just a method of comparing two optical instruments. The larger the light gathering power, the fainter the objects that can be detected (also expressed by the limiting magnitude formula below).
ratio of light gathering power = square of aperture of larger instrument / square of aperture of smaller instrument
Example: an 8 inch telescope gathers 4 times more light than a 4 inch telescope (64 / 16 = 4 - note that both measurements must use the same unit, in this case inches). Another example: an 80mm scope gathers about 130 times more light than the naked eye (the maximum aperture of the naked eye is about 7mm so 6400 / 49 = 130.6).
Limiting Magnitude of an Optical Instrument
This one is a little complicated. Limiting magnitude is the magnitude of the faintest object that an average person with fully dark-adapted eyes will be able to detect.
limiting magnitude = 5 x LOG10(aperture of scope in cm) + 7.5
LOG10 is "log base 10" or the common logarithm. This formula would require a calculator or spreadsheet program to complete. Example: considering an 80mm telescope (8cm) - LOG(8) is about 1.9, so limiting magnitude of an 80mm telescope is 12 (5 x 1.9 + 7.5 = 12). Be certain you multiply 5 times the LOG value before you add 7.5).
Info taken from here:
http://www.nexstarsite.com/_RAC/articles/formulas.htm
Magnification of a Telescope
The most commonly used formula in amateur astronomy is used to calculate the magnification of a telescope:
magnification = focal length of telescope / focal length of eyepiece
Example: using a 10mm eyepiece in a telescope with a focal length of 1000mm results in a magnification of 100x (1000 / 10 = 100).
Maximum Magnification of a Telescope
Since we can simply use different eyepieces to reach different magnification, the temptation is to "pump-up" the power as high as possible. In theory and practice, a telescope with excellent optics is limited to a magnification of about 2 times the aperture (diameter of main object) measured in millimeters. Example: an 80mm refractor is limited to a maximum magnification of about 160x (80 x 2 = 160). Multiply inches by 25.4 to convert to millimeters.
Focal Ratio of a Telescope
The focal ratio of a telescope is mostly used when considering exposure time for astrophotography, but it is also a general characteristic of the telescope that can be useful in other discussions.
focal ratio = focal length of telescope / aperture of telescope
The result is written as f/focal ratio. Example: an 80mm telescope with an 800mm focal length has a focal ratio of f/10 (800 / 80 = 10 - note that both measurements must use the same unit, in this case mm).
Exit Pupil
The exit pupil of an instrument is the cylinder of light leaving the eyepiece. If the exit pupil is larger than the diameter of the fully opened (dark-adapted) pupil of your eye, some of the light will be wasted. Younger eyes typically have a maximum pupil of about 7mm; older eyes may be limited to 5 or 6mm. Various focal lengths and magnifications result in differing exit pupils.
exit pupil for binoculars = aperture of binocular in mm / magnification of binocular
Example: 10x50 binoculars have an aperture of 50 (the second number) and a magnification of 10 (the first number). The exit pupil of these binoculars would be 5mm (50 / 10 = 5).
exit pupil for telescope = focal length of eyepiece / focal ratio of telescope
Actually just a mathematical rearrangement of the formula given for a pair of binoculars, but this formula turns out to be much easier to work with. Example: using a 25mm eyepiece in a telescope with a focal ratio of f/10 results in an exit pupil of 2.5mm (25 / 10 = 2.5).
True Field of View
The true field of view (TFOV) of an instrument is a measurement of the actual field of view seen through the eyepiece. For example, the field of view might show about 1 degree of the sky at a time. A wider field of view is desirable for extended objects such as large nebula and open clusters. Calculation of the TFOV requires the apparent field of view (AFOV) of the eyepiece in use. This is a statistic available from the eyepiece manufacturer, but it is useful to note that most Plossls have an AFOV of about 50 degrees.
TFOV = AFOV of eyepiece / magnification given by eyepiece
Example: a 10mm Plossl with an AFOV of 50 degrees is used in a telescope of 1000mm focal length. The magnification given by this eyepiece is 100x (1000 / 10) so the TFOV is a half degree (50 / 100 = 0.5).
Resolving Limit
The resolving limit of an instrument is an expression of the smallest detail that can be detected by the instrument. The unit of measure is arcseconds (1/3600th of a degree) and a common test is detecting separation in the components in a very close double star. There are two commonly used calculations:
Rayleigh Limit = 5.5 / aperture of telescope in inches
Dawes Limit = 4.56 / aperture of telescope in inches
Example: the Rayleigh Limit for a telescope with a 6 inch aperture is approximately 0.9 arcseconds (5.5 / 6 = 0.92). To convert an aperture given in millimeters (mm) to inches, simply divide the millimeters by 25.4; for example, an 80mm aperture is 3.15 inches.
Light Gathering Power
This is not really an absolute measurement but rather just a method of comparing two optical instruments. The larger the light gathering power, the fainter the objects that can be detected (also expressed by the limiting magnitude formula below).
ratio of light gathering power = square of aperture of larger instrument / square of aperture of smaller instrument
Example: an 8 inch telescope gathers 4 times more light than a 4 inch telescope (64 / 16 = 4 - note that both measurements must use the same unit, in this case inches). Another example: an 80mm scope gathers about 130 times more light than the naked eye (the maximum aperture of the naked eye is about 7mm so 6400 / 49 = 130.6).
Limiting Magnitude of an Optical Instrument
This one is a little complicated. Limiting magnitude is the magnitude of the faintest object that an average person with fully dark-adapted eyes will be able to detect.
limiting magnitude = 5 x LOG10(aperture of scope in cm) + 7.5
LOG10 is "log base 10" or the common logarithm. This formula would require a calculator or spreadsheet program to complete. Example: considering an 80mm telescope (8cm) - LOG(8) is about 1.9, so limiting magnitude of an 80mm telescope is 12 (5 x 1.9 + 7.5 = 12). Be certain you multiply 5 times the LOG value before you add 7.5).
Info taken from here:
http://www.nexstarsite.com/_RAC/articles/formulas.htm
Clear skies~
Re: Some useful info for freshies
Good stuff Desmond. Thanks for sharing!
http://www.astro.sg
email: gary[at]astro.sg
twitter: @astrosg
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.
email: gary[at]astro.sg
twitter: @astrosg
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.