Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

# Parallax

## Recommended Posts

Modern astronomers use parallax to determine the distance to a star. After the observer on the earth propagates the distance of the earth's orbital diameter in a six month time interval (fig 33), the change in the angular position of the star is used to determine the distance to the star but the distance to a 4.22 light year star (4 x 1016 meters) is more than 10times larger than the earth's orbital diameter (2.99 x 1011 m). The earth's orbital diameter is too short of a distance to produce a change in the angular position that can be used to measure the distance to a 4.22 ly star. The resolution required to determine the distance to a 4.22 ly star is calculated using,

A/B = cos θ.........................................................................................................................................78

when A/B  0, equation 78 becomes,

A/B = θ.................................................................................................................................................79

Using A as the earth's orbital diameter, B is the distance to a 4.22 ly star, the resolution θ required to determine the distance to a 4.22 ly (4 x 1016 meters) star is calculated,

θ = A/B = (2.99 x 1011 m) / (4 x 1016 meters) = 7.475 x 10-6 degrees or 0.027 arcsec....................80

To measure the distance of a 4.22 ly star using the earth's orbital diameter as the parallax reference distance requires a telescopic resolution of 0.027 arcsec (equ 80) which is 3.7 times more power than the Hubble (.1 arcsec). The Hipparcos telescope is described with a resolution of .001 arcsec but the Hubble was launched after the Hipparcos and the Hubble's mirror diameter is 7.9 feet which is eight times larger than the Hipparacos mirror diameter (11 inches) yet the Hipparcos is 100 times more powerful than the Hubble which violates logic. Using A/B = θ when A/B  0, the maximum distance to a star calculated using the Hubble is,

B = A/θ = (2.99 x 1011 m) (3600) / (.1 arcsec) = 1.0764 x 1015 m = 0.114 light years.........................81

##### Share on other sites

If the maximum distance that can be determine is less than one light year is modern astronomy a fabrication similar to the photos of the Milky Way galaxy and the LIGO.

##### Share on other sites

Have a look at this.

Parralax can be measured to close stars with amateur telescopes.

##### Share on other sites
Posted (edited)
On 11/04/2019 at 23:59, alright1234 said:

θ = A/B = (2.99 x 1011 m) / (4 x 1016 meters) = 7.475 x 10-6 degrees or 0.027 arcsec....................80

Ah, you've missed the conversion between Radians (which is what A/B gives - technically it's sin-1 (A/B), and degrees.

Multiply by 180/pi and you get the right value of just over 1.5 arc seconds for 4.22 ly.

ETA

parallax itself is defined as the half angle, where 'A' is the earth's orbital radius rather than diameter

Edited by Gfamily

##### Share on other sites
Posted (edited)

I did a talk to my local AS about how Bessel measured the parallax of 61 Cygni - which was done using a telescope where the 6" objective was split, with half on a micrometer thread to allow the distance between the 'nearby' star and a distant star to be measured.

Of course, he measured the separation between 61 Cyg and two other stars over a year,

and from this (despite what looks like a dodgy measurement in Jan 1838), you can see the annual change in parallax

Edited by Gfamily

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×