Definitions

1. Arc seconds are sometimes used to define the measurement of a sky object's angular diameter.

Resolution

1. So, a 100mm objective lens would have 1.2 arc seconds of resolution.

Nebula

1. The bright portion of the nebula is apparently expanding at a rate of 6.8 arc seconds per year, leading to an estimated age of 3000 to 4000 years, i.e.
2. The nebula has a diameter of about 30 arc seconds and a visual brightness of about 9th magnitude.

Magnitude

1. At about the same time, J. Palisa (Vienna, Austria) also found the comet shining like a star of magnitude 8, and gave the coma diameter as 20 arc seconds.

Telescope

1. Its diameter is now below 10 arc seconds, making detail hard to see in a telescope.
2. In metric units, this is: Resolving power (in arc seconds) = 116 divided by aperture of telescope (in millimeters).

Large Telescope

1. Through a large telescope, the planet appears as a blue-green disk with a diameter of about 3.5 arc seconds.

Red Planet

1. When the Red Planet reaches opposition - a rather unfavorable one - on January 29, it shines at magnitude -1.3 and subtends 14.1 arc seconds.

Degrees

1. Remember, an extra 20 minutes per year would mean the celestial sphere shifts 5 degrees every year, and 50 arc seconds per day.
2. It is tipped by 5 degrees 9' (5 degrees 9 arc seconds) to the plane of the Earth's orbit around the sun and this tilted to ecliptic by same amount.

Sun

1. Light requires about 8.3 minutes to arrive from the Sun, during which time the Sun seems to move through an angle of 20 arc seconds.
2. The Sun, as mentioned earlier, has an aberration of just over 20 arc seconds.

Apparent Size

1. Mars increases in apparent size by 1.4 arc seconds and brightens by more than half this month.

Fully Multi-Coated

1. The objective is fully multi-coated and has a resolving power of 1.9 arc seconds.

Angular Diameter

1. Binoculars will easily show it and a small telescope will show a blue-green disc just under 4 arc seconds in angular diameter.

Arc Seconds

1. The FoV is an angular size, measured in degrees, arc minutes, or arc seconds.
2. Angular distance is expressed in degrees, radians, arc minutes (one-sixtieth of a degree), or arc seconds (one-sixtieth of a minute).

Categories

1. Arc Minutes
2. Manufacturing > Measurement > Angle > Angular Diameter
3. Fully Multi-Coated
4. Resolving Power
5. Apparent Size
6. Books about "Arc Seconds" in Amazon.com
   

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