<blockquote>
  <p>the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T).</p>
</blockquote>

<p>That's the frequency of how often the signals occur, <em>not</em> the frequency of the waves they emit. Just compare it to a lighthouse, which has a signal period of a few seconds but a wave frequency of <span class="math-container">$10^{15}$</span> Hz.</p>

<p>The first known pulsars, for example "Little Green Man" or <a href="https://en.wikipedia.org/wiki/PSR_B1919%2B21" rel="nofollow noreferrer">PSR B1919+21</a>, were radio pulsars; your graph shows those waves <em>are</em> detectable from Earth's surface. I stumbled upon <a href="https://academic.oup.com/mnras/article/431/4/3624/1161659" rel="nofollow noreferrer">this article</a> which lists the frequency of some of the pulsars:</p>

<blockquote>
  <p>After the discovery of pulsars at 81.5 MHz (Hewish et al. 1968), the first pulsar detected at 40 MHz was PSR B1133+16 (Arecibo Observatory, 1968, unpublished). In 1969–1970 the pulsars PSR B1133+16 and B0809+74 were detected at 25 MHz (Bruck 1970).</p>
</blockquote>

<p>Below is the full detection range for the telescopes:</p>

<blockquote>
  <p>Therefore joint observations (simultaneous or not) will be highly beneficial, providing a continuous frequency coverage from 8–240 MHz.</p>
</blockquote>

<p>which is roughly equivalent to wavelengths of 40m to 1m.</p>

<p>X-ray pulsars like <a href="https://en.wikipedia.org/wiki/Centaurus_X-3" rel="nofollow noreferrer">Centaurus X-3</a> were discovered later, and not by telescopes on the surface:</p>

<blockquote>
  <p>Centaurus X-3 was first observed during experiments of cosmic X-ray sources made on May 18, 1967. These initial X-ray spectrum and location measurements were performed using a sounding rocket.</p>
</blockquote>

CC BY-SA 4.0
2019-05-25T17:34:36.980Z
This 100% answers my question. Thanks Glorfindel.
pulsardork
CC BY-SA 4.0
2019-05-26T04:07:21.370Z
An additional consideration for radio pulsars: the dispersion delay and broadening of the pulse (and therefore the timing precision) caused by the interstellar plasma scales with frequency^{-2}. This makes higher frequencies better for precise timing and a frequency range is used to estimate the dispersion. See [this figure](https://www.cv.nrao.edu/course/astr534/images/PSRs_scattering.png) of pulse shapes at different frequencies (from [this course](https://www.cv.nrao.edu/~sransom/web/Ch6.html) which also shows the discovery chart recordings of the pulses from "LGM1" or PSR B1919+21)
astrosnapper
CC BY-SA 4.0
2019-05-24T19:58:51.083Z
2019-05-24T19:58:51.083Z
Glorfindel
<p><a href="https://arxiv.org/abs/1801.04318" rel="nofollow noreferrer">This paper on Arxiv</a> indicates that the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T). I have an EE background and it's a long story how I ended up here, but suffice it to say I'm weak on astronomy.</p>

<p><a href="https://en.wikipedia.org/wiki/Radio_telescope#/media/File:Atmospheric_electromagnetic_opacity.svg" rel="nofollow noreferrer">This chart on Wikipedia</a> implies that the entire range of pulsar frequencies should be absorbed by the atmosphere, but <a href="http://pulsarsearchcollaboratory.com/wp-content/uploads/2016/01/PSC_search_guide.pdf" rel="nofollow noreferrer">this guide</a> and even <a href="https://www.rtl-sdr.com/amateur-pulsar-observations-rtl-sdr/" rel="nofollow noreferrer">this budget RF telescope writeup</a> clearly state that pulsars <em>can</em> be detected from Earth's surface.</p>

<p>My questions is: how are pulsars detected from Earth--what am I missing here? Are RF telescopes simply that receptive? Any insights appreciated.</p>

<radio-astronomy><pulsar>
How are pulsars detected from Earth?
pulsardork
# How are pulsars detected from Earth?

(Asked by: username_0 on 2019-05-24)

[This paper on Arxiv](https://arxiv.org/abs/1801.04318) indicates that the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T). I have an EE background and it's a long story how I ended up here, but suffice it to say I'm weak on astronomy.

[This chart on Wikipedia](https://en.wikipedia.org/wiki/Radio_telescope#/media/File:Atmospheric_electromagnetic_opacity.svg) implies that the entire range of pulsar frequencies should be absorbed by the atmosphere, but [this guide](http://pulsarsearchcollaboratory.com/wp-content/uploads/2016/01/PSC_search_guide.pdf) and even [this budget RF telescope writeup](https://www.rtl-sdr.com/amateur-pulsar-observations-rtl-sdr/) clearly state that pulsars *can* be detected from Earth's surface.

My questions is: how are pulsars detected from Earth--what am I missing here? Are RF telescopes simply that receptive? Any insights appreciated.

**Tags:** radio-astronomy, pulsar

---

## 1 answers

### Answer by username_1 on 2019-05-24. Score: 4 | Accepted answer

> the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T).

That's the frequency of how often the signals occur, *not* the frequency of the waves they emit. Just compare it to a lighthouse, which has a signal period of a few seconds but a wave frequency of $10^{15}$ Hz.

The first known pulsars, for example "Little Green Man" or [PSR B1919+21](https://en.wikipedia.org/wiki/PSR_B1919%2B21), were radio pulsars; your graph shows those waves *are* detectable from Earth's surface. I stumbled upon [this article](https://academic.oup.com/mnras/article/431/4/3624/1161659) which lists the frequency of some of the pulsars:

> After the discovery of pulsars at 81.5 MHz (Hewish et al. 1968), the first pulsar detected at 40 MHz was PSR B1133+16 (Arecibo Observatory, 1968, unpublished). In 1969–1970 the pulsars PSR B1133+16 and B0809+74 were detected at 25 MHz (Bruck 1970).

Below is the full detection range for the telescopes:

> Therefore joint observations (simultaneous or not) will be highly beneficial, providing a continuous frequency coverage from 8–240 MHz.

which is roughly equivalent to wavelengths of 40m to 1m.

X-ray pulsars like [Centaurus X-3](https://en.wikipedia.org/wiki/Centaurus_X-3) were discovered later, and not by telescopes on the surface:

> Centaurus X-3 was first observed during experiments of cosmic X-ray sources made on May 18, 1967. These initial X-ray spectrum and location measurements were performed using a sounding rocket.

> **Comments:**
> **username_0**: This 100% answers my question. Thanks Glorfindel.  
> **username_2**: An additional consideration for radio pulsars: the dispersion delay and broadening of the pulse (and therefore the timing precision) caused by the interstellar plasma scales with frequency^{-2}. This makes higher frequencies better for precise timing and a frequency range is used to estimate the dispersion. See [this figure](https://www.cv.nrao.edu/course/astr534/images/PSRs_scattering.png) of pulse shapes at different frequencies (from [this course](https://www.cv.nrao.edu/~sransom/web/Ch6.html) which also shows the discovery chart recordings of the pulses from "LGM1" or PSR B1919+21)  

---

