SSOs and DSOs

[spurius]

Stuff like Proxima Centauri, Sirius and M101 are classed as deep sky objects im assuming because they are mega distant. Stuff like Charon or Mars dont because they are a bit closer. So if a one off comet were to head towards the sun, at what point would it change from "deep sky object" to a shallow sky one by definition?

Why does sirius look so crazy through a telescope? I heard its something to do with the way atmosphere screws with light, but venus and other bright objects sometimes look really bad but they dont look like a fuzzy ball of colour.

Somewhat more powerful than my scope but its basically what I see.

[John]

My understanding of the term deep sky object is that it generally relates to objects that are outside the solar system. Comets are solar system objects so not deep sky objects.

Sirius scintillates like that because it's a bright point source that is relatively low in the sky from the UK so it's being observed through more of the atmosphere which refracts the light causing the colours. In some scopes it can be bought to a tighter focus and it's possible to see the faint white dwarf star Sirius B shining faintly very close to the bright Sirius A.

[ronin]

Comets etc are solar objects so not DSO's.

Basically if bound to the sun then solar, if concerned with another star or further then DSO.

You could term them Solar and Extra-Solar.

[Knight of Clear Skies]

The definition of DSO is a little vague, individual stars such as Sirius are excluded; it is typically used to describe extended objects, such as nebulas, star clusters and galaxies. By that definition a comet would never be described as a DSO.

[Moonshane]

well I have learned something. I always thought it was deep space objects! Sirius surely is a DSO though as it's a double (not an individual) star? many of my books refer to doubles as being DSOs.

[Black Knight]

My understanding of the term deep sky object is that it generally relates to objects that are outside the solar system. Comets are solar system objects so not deep sky objects.

That's how I always understood it as well. Everything outside the solar system = DSO.

[Knight of Clear Skies]

Browsing some more, some definitions include multiple star systems such as Sirius, while others don't, and some people include single stars as well. It's not a precise term, the first two definitions I found conflict with each other.

'An object in the night sky other than a solar system object, single star or multiple star system.'

'Deep-Sky Objects. Deep-sky objects can be loosely defined as all objects outside our solar system that consist of more than a single star system or involve nebulosity.'

[spurius]

I always assumed stuff outside the solar system was DSO. When I said comets, I meant the kind that originated elsewhere and happened to travel into our solar system. I know most comets are periodic, or bound to our sun by its gravity. Was wondering where the actual boundary of what they consider our solar system is. Sedna? Kuiper belt or outer reaches of oort cloud?

[pete_l]

'Deep-Sky Objects. Deep-sky objects can be loosely defined as all objects outside our solar system that consist of more than a single star system or involve nebulosity.'

Yes, I've always considered a DSO to be something (outside the solar system)that resolves to a visible size in a telescope - thus making it an "object". So stars are still pinpoints, hence not DSOs, but star clusters, galaxies, planetary nebs etc. would be classed as DSOs.

As others say, the boundaries are murky - when does a multiple star system become a cluster?

However, since it's a hobby - not an exam question - the actual definition makes little difference to me.

[Stargazer_00]

Scintillation fascinates me ever since I first saw it on Sirius.

This is a star trail (lifted from the internet) which depicts the changing colouration well I think

http://dcer.smugmug.com/Photography/Sky-Stuff/i-H6CDNM4/0/O/IMG_3450.jpg

[Knight of Clear Skies]

I always assumed stuff outside the solar system was DSO. When I said comets, I meant the kind that originated elsewhere and happened to travel into our solar system.

I think this would be termed an interstellar comet; in theory, they should be very common. Comets have been observed to achieve hyperbolic (escape) orbits after interacting with a solar system body, but none have been observed entering the inner solar system on a hyperbolic trajectory, which would be evidence of extra-solar origin.

Some astronomers think the unusual comet 96P/Macholz could be an extra-solar comet captured by Jupiter. It has an atypical orbit and composition.

Was wondering where the actual boundary of what they consider our solar system is. Sedna? Kuiper belt or outer reaches of oort cloud?

One way to look at this is to consider the Sun's Hill sphere, the region where the Sun's gravity dominates, within which other bodies can orbit the Sun. This has a radius of approximately 1 light year - the Oort cloud is thought to be a little smaller, because other effects such as radiation pressure make orbits towards the edge of a Hill sphere unstable.

However, since it's a hobby - not an exam question - the actual definition makes little difference to me.

Hope my first post didn't cause too much confusion. I looked it up, and the first definition I found matched what I thought it was, but actually people use the term slightly differently, so there is no right answer. The term DSO originates from a column in a 1940s astronomy magazine.