How far can you see with your telescope?

[alocky]

I often get asked this by non-astronomy friends, and until now have been unsure how to answer them.
Last night I was playing with two nights worth of data on the M77 region, and used the aladin server to identify some of the pinpricks of light. One of them is a quasar with a redshift of 0.67. Using a simple cosmological model gives a Hubble distance of 2474Mpc, or 8.068 billion light years, about half the age of the universe. That's my new answer!
Cheers
Andrew.

[el_draco]

Take a couple of more nights and see what happens... ;)

[silv]

super cool answer and way to find it :D

[OzEclipse]

How far can you see is a different Q to how far can you photograph?

3C 273 in Virgo. Mag 12.9. Saw it in my 6 inch reflector years ago. 2 billion light years away.

Joe

[mental4astro]

This is the one question that most gets my goat. Most people ask it as this is the most 'intelligent' question they can come up with on a topic they are completely ignorant about.

The hardest part about it is the provide an answer that isn't condescending, jargon filled, or smart arse.

I've always struggled with my 'normal' response that "a scope is to collect light, not "see how far" ". This actually means nothing to these good folk.

To throw out "about 2 billion light years" is smart arse-ish too, as many people also struggle with the concept of the distances involved. Especially with the way the media throws around "one billion dollars" or "100 billion dollars", the concept of dollars and distance, 2 billion light years is really just around the corner for most people...

A quick, insightful and respectful reply to a fleeting question is really difficult. And to get too technical, we run the risk of looking too smart for our own good and we've lost any interest from the person we are engaging. Only adding to the difficulty that anything "astro" in the mind of most people is immediately associated with "rocket science" and "too difficult to comprehend", in no kind way due to the way things astro are presented in the general media.

Of course, much of the response has to do with the context the question is posed in. A response at an outreach event would need to be different from a casual meeting with someone, and the Virgo quasar is perfectly fine at an outreach night. And really it is the casual meeting that most causes me trouble.

Please excuse my philosophical musing. I love engaging with people on things astro, and doing so in ways that breaks down the mindset most people have about physics - which is what this is all about.

Hey, on another thing, but related to outreach, there's one thing I've started mentioning to people at outreach nights. I try to bring into the conversation the topic of gold. I ask people if they are wearing any gold, or think about the gold they have at home. All that gold they are wearing was created in the cataclysmic explosion of a supermassive star, that spewed its guts out, and you are now wearing a little bit of that material... Pretty cool I reckon, :)

Alex.

[Slawomir]

Alex, as you have mentioned, your response must depend on who is asking. I suggest not providing any numbers, as theses are hard to visualise, unless someone really wants a number. In fact, the same applies to any aspect of life in which someone demonstrates a bit more expertise.

[alocky]

Interesting spread of perspectives shown here. I do a lot of outreach work at Perth observatory and agree completely that an answer of 2457 megaparsecs isn't very edifying. But the key is to provide multiple answers, and not get hung up on having too many significant figures. I think if you're questioner's eyes haven't glazed over it's a great opportunity to talk about cosmological redshift and light years. Being a geo I usually relate it to whatever the dominant megafauna were roaming our planet at the time the light left, but in this case - twice the age of the earth will do, or half the time since the Big Bang.
Condescension, arrogance or irritation are never tools I would use when talking to friends, or for that matter anyone who asks a genuine question in good faith. Regardless of how superior we astronomers are in every way, there's a good chance anyone you're talking to knows more about something than you do.

[clive milne]

Adopting the scientific method... it may be more useful to say; the furthest you can ever possibly hope to see is 13.7 billion light years... your mileage may vary.

[mental4astro]

Clive, your reply just triggered another possible twist as a reply:

It would be fair to say to pretty much anyone that "my scope is a time machine, and I can see as far back as 2 billion years". Completely factual and non scientific, and in a way that everyone can relate to.

I can expand a little further and say "And I can also look upon the time when the dinosaurs were wiped out, 64 million years ago (the Grus Quartet)".

Interesting reply option.

Alex.

[silv]

and what about looking through the scope in daylight?
How far can you see?

[mental4astro]

Easy - nine light minutes, 1AU (astronomical unit), or 150,000,000km - take your pick on the units... the distance to the Sun.

Now that's excluding any supernovae that might pop up... as smart arse a reply as I can muster this last quip, :rolleyes::D::P::lol:

[mental4astro]

No! I'm mistaken!

Easily at least 860 light years - Rigel!

That'll also spin out some people that you can see stars during the day! :)

[clive milne]

A couple of thousand light years is relatively easy... (Rigel, Betelgeuse... et al).. In theory, quite a bit further... down to about 4th magnitude if you have a couple of meters aperture at your disposal... Which I suppose would put you out around 10 to 20K light years.

[silv]

okayokayokay -
huge stars, alright.

and how far if you point the scope towards the eastern horizon? Can you see ... Mount Ruapehu?
How far away can you make out details if you look straight ahead?
Can you see something on the horizon that I can not see with my eyes?

[silv]

and once this is established as a comparison everyone can relate to -

then you or we can fall into the rant where "kilometres" suddenly become "years".

[AstralTraveller]

I tend to say "Hmmmm ... that's a tricky one. I can certainly see very bright objects whos light has taken billions of years to get here but I can't see nearby very faint objects. It's easier to talk about how faint I can see than how far." I can then discuss absolute mag vs. apparent mag and the magnitude scale (without the jargon).

BTW people also tend to assume that DSOs are all very small and require very high magnifications. They tend to be very surprised when I say I'm using 'only 60x', the object we are looking at is bigger than the full moon and the reason you can't see it naked eye is that it is too faint, not too small.

[yoda776]

Not so much spin out for me but how do you find and track them during the day? Setup early morning or is ther a particular 'scientific' method?

[noeyedeer]

they could be asking "how far you can see" on earth based objects ...sorry taking it to another lower level. I guess the horizon is the limiting factor for that one. I think for me if I said I can see inside apartments in surfers from around 15km away would blow their minds
matt

[noeyedeer]

alt-Az or ra/Dec coordinates.. point the scope and see if it's there
matt

[Marko of Oz]

My telescope doesn't let me see further, it just magnifies stuff, like my reading glasses. :)