Foreground & Background in Astrophysical Observation

[atomiclaser]

TL;DR

definition of foreground and background in astrophysical observation

During the astrophsyical observation, what is the definition of foreground and background in astrophysical observation?

 

[jedishrfu]

I don't think there's a hard and fast definition. Foreground objects are in front of the object you are looking at and affect your viewing of the object.

An example, would be taking a photo of the Andromeda galaxy. The photo will be littered with foreground stars from our own galaxy and taking any measurements from the observation would require knowing what stars are what and how far away they are so that foreground stars can be eliminated. Parallax is often used to eliminate these stars as they will move depending on where we take our photo ie spring time vs fall time when we are at opposite ends of the Earth orbit.

Early universe objects are affected by lensing, dust clouds absorbing light, expansion ... and many other effects that must be accounted for to get your measurements.

Background objects

The Openstax online Astronomy may answer more of your questions.

https://openstax.org/details/books/astronomy

 

[snorkack]

Say you are observing a star cluster - a group of stars embedded in Milky Way disc, spatially together, but also sharing a common peculiar motion and astrophysical origin.
You can distinguish foreground objects. Like Aldebaran in front of Hyades.
And there are stars behind Hyades.
But suppose you can identify a star that is physically in the middle of Hyades - but has a different peculiar velocity and origin.
Which -ground is it? It is neither foreground nor background...

 

[atomiclaser]

I don't think there's a hard and fast definition. Foreground objects are in front of the object you are looking at and affect your viewing of the object.

An example, would be taking a photo of the Andromeda galaxy. The photo will be littered with foreground stars from our own galaxy and taking any measurements from the observation would require knowing what stars are what and how far away they are so that foreground stars can be eliminated. Parallax is often used to eliminate these stars as they will move depending on where we take our photo ie spring time vs fall time when we are at opposite ends of the Earth orbit.

View attachment 263845View attachment 263846View attachment 263847

Early universe objects are affected by lensing, dust clouds absorbing light, expansion ... and many other effects that must be accounted for to get your measurements.

Background objects

The Openstax online Astronomy may answer more of your questions.

https://openstax.org/details/books/astronomy

thanks for your explanation.

 

[atomiclaser]

that means there are some other star or galaxy beyond the interested astrophysical object, the lumination from them could be called foreground. If I understand correctly, all the astrophysical obsevation has foreground and background, these consist of the whole observation. The pictures often shown is filtered out the foreground and background, right?