Hubble Constant Question

On Tue, 20 Apr 2004 15:33:37 -0700, in uk.sci.astronomy , "Hannah
Parkinson" wrote:

Can anyone help me?
I've been given a report to write about calculating the hubble constant
using standard rods. I've caluculated the hubble constant for 15 galaxies
from the hubble deep field. The instructions i have were to plot these
values against the recession velocity for each galaxy and observe a trend.
Done that. But what causes the trend (increasing hubble constant with
velocity) and how do i remove it?

A websearch might be useful for you. Learning to google is an invaluable
tool these days.

My own websearch suggested that what you're seeing is the rate of change of
expansion of the universe. Its slowing, so the hubble constant is becoming
less as time passes. Distant galaxies represent earlier time periods and
thus have a higher hubble constant.

You can't remove this, unless you happen to be the Creator. :-)

--
Mark McIntyre
CLC FAQ http://www.eskimo.com/~scs/C-faq/top.html
CLC readme: http://www.angelfire.com/ms3/bchambless0/welcome_to_clc.html


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Can anyone help me?
I've been given a report to write about calculating the hubble constant
using standard rods. I've caluculated the hubble constant for 15 galaxies
from the hubble deep field. The instructions i have were to plot these
values against the recession velocity for each galaxy and observe a trend.
Done that. But what causes the trend (increasing hubble constant with
velocity) and how do i remove it?

"Hannah Parkinson" wrote in message
...
Can anyone help me?
I've been given a report to write about calculating the hubble constant
using standard rods. I've caluculated the hubble constant for 15 galaxies
from the hubble deep field. The instructions i have were to plot these
values against the recession velocity for each galaxy and observe a trend.
Done that. But what causes the trend (increasing hubble constant with
velocity) and how do i remove it?



I'm not sure you are plotting the right things. Usually the "Hubble plot"
is of measured velocity in km/s (or redshift) on the y-axis, and distance on
the x-axis. (Distance units are usually in Megaparsecs). Then, the Hubble
constant is the slope of the best fit line passing through the points. Part
of the experiment may involve deriving the distance modulus (involving
magnitudes) from standard brightness objects like cepheid variables or type
Ia supernovae and converting to distances.

What you are doing sounds more like this. If you did it correctly, you
should find the slope to be around 70 km/sec per Megaparsec.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

I have been searching the web for a lot of hours and nothing turned up.
According to my instructions for the report i should be able to remove it
easily. I also tried putting in approximately where each galaxy should be
now which reduced the gradient but didn't get rid of it. I think i'm still
missing something.


"Etok" wrote in message
...
Mark McIntyre wrote:


My own websearch suggested that what you're seeing is the rate of change
of
expansion of the universe. Its slowing, so the hubble constant is
becoming
less as time passes. Distant galaxies represent earlier time periods and
thus have a higher hubble constant.

You can't remove this, unless you happen to be the Creator. :-)


Hey, I thought the rate of expansion was *increasing*, owing to "dark
energy".
Am I missing something?
If I am, it's pretty big.

Regards,
Etok


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I have also done that graph and have the Hubble constant between 24 and
93ish so that's fine from the data we were given it's just this other graph
we were told to plot. I don't really know what it's for or why there is a
trend in the hubble constant calculated for each individual galaxy.

We weren't given data from cepheid variables we were only given standard rod
data for spirals and ellipticals.

"Mike Dworetsky" wrote in message
...


"Hannah Parkinson" wrote in message
...
Can anyone help me?
I've been given a report to write about calculating the hubble constant
using standard rods. I've caluculated the hubble constant for 15
galaxies
from the hubble deep field. The instructions i have were to plot these
values against the recession velocity for each galaxy and observe a
trend.
Done that. But what causes the trend (increasing hubble constant with
velocity) and how do i remove it?



I'm not sure you are plotting the right things. Usually the "Hubble plot"
is of measured velocity in km/s (or redshift) on the y-axis, and distance
on
the x-axis. (Distance units are usually in Megaparsecs). Then, the
Hubble
constant is the slope of the best fit line passing through the points.
Part
of the experiment may involve deriving the distance modulus (involving
magnitudes) from standard brightness objects like cepheid variables or
type
Ia supernovae and converting to distances.

What you are doing sounds more like this. If you did it correctly, you
should find the slope to be around 70 km/sec per Megaparsec.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

On 21 Apr 2004 04:49:27 GMT, in uk.sci.astronomy , Etok
wrote:

Mark McIntyre wrote:


My own websearch suggested that what you're seeing is the rate of change of
expansion of the universe. Its slowing, so the hubble constant is becoming
less as time passes. Distant galaxies represent earlier time periods and
thus have a higher hubble constant.

You can't remove this, unless you happen to be the Creator. :-)


Hey, I thought the rate of expansion was *increasing*, owing to "dark
energy".

There seems to still be some disagreement about whether it is or not, and
some research I've seen on the web suggests that Ho is lower for more
distant galaxies (the reverse of what Hannah saw).

But if it is speeding up, its not dark matter thats doing it, that would
have the reverse effect, wouldn't it?


--
Mark McIntyre
CLC FAQ http://www.eskimo.com/~scs/C-faq/top.html
CLC readme: http://www.angelfire.com/ms3/bchambless0/welcome_to_clc.html


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"Hannah Parkinson" wrote in message ...
I have also done that graph and have the Hubble constant between 24 and
93ish so that's fine from the data we were given it's just this other graph
we were told to plot. I don't really know what it's for or why there is a
trend in the hubble constant calculated for each individual galaxy.

We weren't given data from cepheid variables we were only given standard rod
data for spirals and ellipticals.

Look at the "standard rod data for spirals and ellipticals"
are there any effects due to brightness, red-shift and/or evolution
which are unaccounted for?

RonL


"Mike Dworetsky" wrote in message
...


"Hannah Parkinson" wrote in message
...
Can anyone help me?
I've been given a report to write about calculating the hubble constant
using standard rods. I've caluculated the hubble constant for 15
galaxies
from the hubble deep field. The instructions i have were to plot these
values against the recession velocity for each galaxy and observe a
trend.
Done that. But what causes the trend (increasing hubble constant with
velocity) and how do i remove it?



I'm not sure you are plotting the right things. Usually the "Hubble plot"
is of measured velocity in km/s (or redshift) on the y-axis, and distance
on
the x-axis. (Distance units are usually in Megaparsecs). Then, the
Hubble
constant is the slope of the best fit line passing through the points.
Part
of the experiment may involve deriving the distance modulus (involving
magnitudes) from standard brightness objects like cepheid variables or
type
Ia supernovae and converting to distances.

What you are doing sounds more like this. If you did it correctly, you
should find the slope to be around 70 km/sec per Megaparsec.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)