Estimating Time to Record Faint Star on Telescopes

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In summary: A telescope with a 1.2m mirror can record the image of a faint star in 1 hour. However, if you place a telescope in space with the same mirror size, it will only be able to record the image of the star for 0.25 seconds. This is because the atmosphere causes the light from the star to be scattered and reduced in brightness.
  • #1
joker_900
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Homework Statement


An earth-based telescope with a mirror of diameter 2.4 m can record the im-
age of a faint star in 1 hour. A telescope placed in space (above the atmosphere)
has a mirror of the same focal length as that of the earth-based instrument, but
its diameter is 1.2 m. Atmospheric turbulence is assumed to place a limit of 0.25
seconds of arc on the angular resolution obtainable by earth-bound telescopes,
and the mean wavelength of the radiation detected is 550 nm. Estimate the
time required by the telescope placed in space to record the same star.


Homework Equations


f no. = focal length/aperture diameter

The Attempt at a Solution


The only thing I can think of is to calculate the f no. (focal length/mirror diameter) for each and say this is proportional to the time (as it is a measure of brightness, and so flux, and the greater the flux the shorter the time). However this would ignore any atmospheric effect of reducing flux.

There is another part to the question, so this part might not need all the information provided.

Thanks
 
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  • #2
That's not a meaningful question.
The resolution doesn't determine the limiting magnitude (assuming an appropriately matched detector) the only effect putting it in space would have is to to remove sky background (which you aren't given) or atmospheric absorption.
 
  • #3
mgb_phys said:
That's not a meaningful question.
The resolution doesn't determine the limiting magnitude (assuming an appropriately matched detector) the only effect putting it in space would have is to to remove sky background (which you aren't given) or atmospheric absorption.

Thanks for replying

There is a second part to the question which may be what the resolution information is for. But how would you go about this first part? What information would I need to determine the affect of the atmosphere on the brightness?

Thanks
 
  • #4
Sorry probably over analysing the question!
The signal received is proportional to the area of the mirror (assuming everything else is the same), so with half the mirror diameter it will have 0.25 the mirror area and a signal rate 4x less.

It's a common mistake from amateur astronomers that the limiting magnitude depends on the f# which is what I thought the question was asking. Although this is true for naked eye observing it isn't true for cameras.
 

1. How long does it take to record a faint star on a telescope?

The time it takes to record a faint star on a telescope depends on several factors, including the size and sensitivity of the telescope, the brightness of the star, and the atmospheric conditions. Generally, it can take anywhere from a few minutes to several hours to record a faint star.

2. What is the minimum magnitude of a star that can be recorded on a telescope?

The minimum magnitude of a star that can be recorded on a telescope varies depending on the size and sensitivity of the telescope. In general, larger and more sensitive telescopes are able to detect fainter stars. However, even with the most powerful telescopes, there is a limit to how faint of a star can be recorded due to background noise and other factors.

3. How accurate are the time estimations for recording faint stars on telescopes?

The accuracy of time estimations for recording faint stars on telescopes can vary depending on the factors mentioned previously. However, with advanced technology and precise calculations, scientists are able to make fairly accurate time estimations for recording faint stars on telescopes.

4. Can multiple faint stars be recorded at the same time on a telescope?

Yes, it is possible to record multiple faint stars at the same time on a telescope. This is often done by using a technique called "drift scanning," where the telescope is pointed at a specific area of the sky and allowed to move slowly as the stars pass through its field of view.

5. How does the location of the telescope affect the time it takes to record a faint star?

The location of the telescope can greatly affect the time it takes to record a faint star. Telescopes located in areas with less light pollution and clearer skies will have an easier time detecting faint stars compared to those in areas with more light pollution and cloudy skies. Additionally, telescopes located closer to the equator may have a longer window of time to observe a particular star compared to those at higher latitudes.

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