Frequently Asked Questions

Astronomy (3)

I saw a bright light in the sky last night. Do you know what it was?

The SAAA does not keep track of unexplained phenomena in the sky, so I cannot tell you for certain what it is that you saw. However, there are several possibilities:

  • First of all, it could not be a supernova because they become very bright for weeks to months, not just for a few seconds. Supernovae that are bright enough for the naked eye to see are also very rare.
  • If the object was moving, there are a few possibilities. If it was near the horizon the object is most likely an airplane with its landing lights on. The brightening and dimming is caused by the plane changing direction. If the object is high in the sky it may be a satellite. These are fairly common. If you are interested in determining whether or not you saw a satellite I recommend looking at the website: Heavens Above. It makes predictions as to what you may see, however it isn’t perfect and it might not predict a satellite that you may have seen.
  • If the object is not moving it is most likely a planet or star. When planets, and especially stars, are low on the horizon they twinkle rapidly, often changing color. If you saw a planet, the reason it disappeared is most likely that a distant cloud, which you could not see, covered it. This is rather common and a likely explanation.

ATM (2)

How do you determine focal length of a telescope’s mirror?

The focal length of a mirror is equal to the focal ratio times the diameter of the mirror. For example, a 1-meter telescope that is f/8 would have a focal length of 8 meters.

Blue Moon (1)

When is the next Blue Moon?

Blue Moon is the name given to the second full moon in a month. Since a full moon occurs every 29 1/2 days, if there is a full moon on the 1st or 2nd day of a month, there is a good chance there will be a second full moon, or blue moon, that month.

In 1999, there were two blue moons very close together. One was January 31st (full moons on the 2nd and the 31st) and another two months later on March 31st (full moons again on the 2nd and the 31st). February had no full moon that year.

After that there was one in November, 2001 (the 1st and the 30th), July 2004, August 2005, June 2007, and we’ll have to wait until May of 2008 for the next Blue Moon.

We won’t see two blue moons in one year again until 2018.

A great web site to check for answers to questions like this is at Ask the Space Scientist. There are several questions in the archives at that site about blue moons, including a table of blue moons through 2028.

Computer (1)

Does anyone know of a good local source for a sheet of red acrylic or plexiglas to use for a laptop screen?

Plastic Supply of San Antonio Inc
102 West Josephine Street
San Antonio, TX 78212
Phone: 210.222.8091

Falklands (1)

What do R.A.F. pilots do for fun in the Falkland Islands?

Noting that the local penguins are fascinated by airplanes, the pilots search out a beach where the birds are gathered and fly slowly along it at the water’s edge. Perhaps ten thousand penguins turn their heads in unison watching the planes go by, and when the pilots turn around and fly back, the birds turn their heads in the opposite direction, like spectators at a slow- motion tennis match. Then, the pilots fly out to sea and then back directly to the penguin colony and overfly it. Heads go up, up, up, and ten thousand penguins fall over gently onto their backs.

Join (1)

How do I join the San Antonio Astronomical Association?

You can print and fill out the membership form and mail it to:

San Antonio Astronomical Association
Post Office Box 701261
San Antonio, Texas 78270-1261

You can also contact our New Member Coordinator.

Leap Years (1)

Where can I find information about leap years?

At the web site Leap Years from the US Naval Observatory

Light in Sky (1)

I saw a bright light in the sky last night. Do you know what it was?

The SAAA does not keep track of unexplained phenomena in the sky, so I cannot tell you for certain what it is that you saw. However, there are several possibilities:

  • First of all, it could not be a supernova because they become very bright for weeks to months, not just for a few seconds. Supernovae that are bright enough for the naked eye to see are also very rare.
  • If the object was moving, there are a few possibilities. If it was near the horizon the object is most likely an airplane with its landing lights on. The brightening and dimming is caused by the plane changing direction. If the object is high in the sky it may be a satellite. These are fairly common. If you are interested in determining whether or not you saw a satellite I recommend looking at the website: Heavens Above. It makes predictions as to what you may see, however it isn’t perfect and it might not predict a satellite that you may have seen.
  • If the object is not moving it is most likely a planet or star. When planets, and especially stars, are low on the horizon they twinkle rapidly, often changing color. If you saw a planet, the reason it disappeared is most likely that a distant cloud, which you could not see, covered it. This is rather common and a likely explanation.

Membership (2)

How do I join the San Antonio Astronomical Association?

You can print and fill out the membership form and mail it to:

San Antonio Astronomical Association
Post Office Box 701261
San Antonio, Texas 78270-1261

You can also contact our New Member Coordinator.

Moon (1)

When is the next Blue Moon?

Blue Moon is the name given to the second full moon in a month. Since a full moon occurs every 29 1/2 days, if there is a full moon on the 1st or 2nd day of a month, there is a good chance there will be a second full moon, or blue moon, that month.

In 1999, there were two blue moons very close together. One was January 31st (full moons on the 2nd and the 31st) and another two months later on March 31st (full moons again on the 2nd and the 31st). February had no full moon that year.

After that there was one in November, 2001 (the 1st and the 30th), July 2004, August 2005, June 2007, and we’ll have to wait until May of 2008 for the next Blue Moon.

We won’t see two blue moons in one year again until 2018.

A great web site to check for answers to questions like this is at Ask the Space Scientist. There are several questions in the archives at that site about blue moons, including a table of blue moons through 2028.

Moonrise (1)

Where can I find information about the sun and moon rising and setting?

You can find the sun and moon rise and set information in planetarium software such as TheSky and SkyMap and on the web at The National Naval Observatory Data Services

Moonset (1)

Where can I find information about the sun and moon rising and setting?

You can find the sun and moon rise and set information in planetarium software such as TheSky and SkyMap and on the web at The National Naval Observatory Data Services

Night Vision (1)

Does anyone know of a good local source for a sheet of red acrylic or plexiglas to use for a laptop screen?

Plastic Supply of San Antonio Inc
102 West Josephine Street
San Antonio, TX 78212
Phone: 210.222.8091

RAF (1)

What do R.A.F. pilots do for fun in the Falkland Islands?

Noting that the local penguins are fascinated by airplanes, the pilots search out a beach where the birds are gathered and fly slowly along it at the water’s edge. Perhaps ten thousand penguins turn their heads in unison watching the planes go by, and when the pilots turn around and fly back, the birds turn their heads in the opposite direction, like spectators at a slow- motion tennis match. Then, the pilots fly out to sea and then back directly to the penguin colony and overfly it. Heads go up, up, up, and ten thousand penguins fall over gently onto their backs.

SAAA (3)

What are the images on the SAAA logo

The galaxies that dominate the logo are known, collectively, as the Whirlpool Galaxy or M51 in the constellation Canes Venatici.  The image immediately above the lettering is the outline of the Alamo, and the image on the left of the logo is the Tower of the Americas.

I saw a bright light in the sky last night. Do you know what it was?

The SAAA does not keep track of unexplained phenomena in the sky, so I cannot tell you for certain what it is that you saw. However, there are several possibilities:

  • First of all, it could not be a supernova because they become very bright for weeks to months, not just for a few seconds. Supernovae that are bright enough for the naked eye to see are also very rare.
  • If the object was moving, there are a few possibilities. If it was near the horizon the object is most likely an airplane with its landing lights on. The brightening and dimming is caused by the plane changing direction. If the object is high in the sky it may be a satellite. These are fairly common. If you are interested in determining whether or not you saw a satellite I recommend looking at the website: Heavens Above. It makes predictions as to what you may see, however it isn’t perfect and it might not predict a satellite that you may have seen.
  • If the object is not moving it is most likely a planet or star. When planets, and especially stars, are low on the horizon they twinkle rapidly, often changing color. If you saw a planet, the reason it disappeared is most likely that a distant cloud, which you could not see, covered it. This is rather common and a likely explanation.

Star Gifting (1)

How do I name a star after my Mother/Father/Girlfriend/Boyfriend/etc?

The International Astronomical Union is the only recognized star-naming organization, and it does not sell names.

There are certain commercial and some nonprofit organizations that may offer a service to “register” a star in someone’s name, generally for a fee, but these are neither sanctioned by the International Astronomical Union (IAU) nor used by professional astronomers. Check out this Star Buying FAQ before you “buy a star”.

Sunrise (1)

Where can I find information about the sun and moon rising and setting?

You can find the sun and moon rise and set information in planetarium software such as TheSky and SkyMap and on the web at The National Naval Observatory Data Services

Sunset (1)

Where can I find information about the sun and moon rising and setting?

You can find the sun and moon rise and set information in planetarium software such as TheSky and SkyMap and on the web at The National Naval Observatory Data Services

Telescope (2)

How do you determine focal length of a telescope’s mirror?

The focal length of a mirror is equal to the focal ratio times the diameter of the mirror. For example, a 1-meter telescope that is f/8 would have a focal length of 8 meters.

Telescope Making (2)

How do you determine focal length of a telescope’s mirror?

The focal length of a mirror is equal to the focal ratio times the diameter of the mirror. For example, a 1-meter telescope that is f/8 would have a focal length of 8 meters.

What is it? (1)

I saw a bright light in the sky last night. Do you know what it was?

The SAAA does not keep track of unexplained phenomena in the sky, so I cannot tell you for certain what it is that you saw. However, there are several possibilities:

  • First of all, it could not be a supernova because they become very bright for weeks to months, not just for a few seconds. Supernovae that are bright enough for the naked eye to see are also very rare.
  • If the object was moving, there are a few possibilities. If it was near the horizon the object is most likely an airplane with its landing lights on. The brightening and dimming is caused by the plane changing direction. If the object is high in the sky it may be a satellite. These are fairly common. If you are interested in determining whether or not you saw a satellite I recommend looking at the website: Heavens Above. It makes predictions as to what you may see, however it isn’t perfect and it might not predict a satellite that you may have seen.
  • If the object is not moving it is most likely a planet or star. When planets, and especially stars, are low on the horizon they twinkle rapidly, often changing color. If you saw a planet, the reason it disappeared is most likely that a distant cloud, which you could not see, covered it. This is rather common and a likely explanation.

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“to promote the study of astronomy and related fields and to pursue observation as a hobby”

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