The Official Astronomy Thread

[dappled]

Well I view JHB as North, so I don't know. I might be completely directionless

"It's all relative"

 

[MisterBigglesworth]

Saw it last night...very kewl. Will apparently pass overhead in Jhb tonight @ 18:05...

 

[AllBrain]

I am going to pickup my new laser collimator and wide angle eyepiece this afternoon. Cannot wait to see what the night sky looks like through the new eyepiece. Will do the collimation after to compare the image.

Then I should really look at a finder scope with a right angle eyepiece as I am breaking my back when the scope points strait up. Maybe even a red dot finder but hell if I know how they work.

 

[Crusader]

RDF are simple. They projecta small red dot on a screen in the finderscope. You keep both eyes open when looking through them and align the dot with the object/area it's supposed to be. It really makes things much easier since you know exactly where the scope is pointed and helps with star hopping (provided you see enough stars). They shouldn't be seen as a replacement of the optical finder but used in conjunction. Once you know where something is and with practice you can point directly at it.

 

[randal]

I don't know alot about astronomy but I'm confused about something ever since I went to visit the planetarium a couple of months ago. Can someone please explain?

The earth rotates around its own axis creating night and day 365 times a year. And the earth completes one orbit around the sun in a year. So in a year every night the earth would be facing in a new angle relative to the sun, completing 360 degree angles in one orbit. Why then do we always see the same stars at night?

 

[dappled]

I don't know alot about astronomy but I'm confused about something ever since I went to visit the planetarium a couple of months ago. Can someone please explain?

The earth rotates around its own axis creating night and day 365 times a year. And the earth completes one orbit around the sun in a year. So in a year every night the earth would be facing in a new angle relative to the sun, completing 360 degree angles in one orbit. Why then do we always see the same stars at night?

We do see different stars through the year. But mostly the stars we see are so far away, that the distance/angle changes don't matter HUGELY.

Imagine a pea, rotating on it's axis, and revolving in an orbit of 20cm distance. Now place this rotating pea, revolving in it's 20cm long orbit, inside a giant transparent ball, like this ball:

now stick the stars onto the outer plastic of the ball. the pea is earth.

 

[randal]

ok I understand that the huge distance will not affect the angels too much, but if I use a picture to describe it:

    ......	 

.     1      . 
.            .
.  4  s  2   . 
.            .
      3

    .....

where s is the sun. 1,2,3,4 is the earth position at 4 quarters of the year. And the .... are the stars. At position 1 and 3, the stars that can be seen would be totally different.

The only exception that makes sense to me is that our solar system also rotates, but in an opposite direction to the earths orbit around the sun?

 

[Crusader]

What you need to keep in mind is that the Earth rotates around it's axis, so it's not pointed in one direction only. The only part of the sky we don't see throughout the year is the part around the sun (from our perspective) the rest can still be seen provided you stay up long enough.

 

[dappled]

ok I understand that the huge distance will not affect the angels too much, but if I use a picture to describe it:

this would be slightly more realistic:

                      .        ..    ..              . . ..              . .           .              ..
.  .                                     .           X             ..       ...             .         . . 
           .              .                                     .                                       .
   .                                                .                                           .
 ..                               .
 .                .                                                         . . .                ..
            .                                                    .           
                             .                          
                                                 .                                                ..   . 
.
      .        . 
           .                                                                                             .

                                  .                                                                      .
.

              . 
.

 ..         .
.
.                                               1                                    . 
. A                                           4 s 2                                               .B
                                                3
                                                                                        .           ...

.
    .
   .           .
 .

              .                                                                                      . 
          .                                                                                    .   .
                                   .
    .                                                                               .. .   .
                   .
                      .        ..    ..              . . ..              . .           .              ..
.  .                                     .                        ..       ...             .         . . 
           .              .                                     .                                       .
   .                                                .                                           .
 ..                               .
 .                .                                  Y                      . . .                ..
            .                                                    .           
                             .                          
                                                 .                                                ..   . 
.
      .        . 
           .                                                                                             .

except now magnify the distances A-B and X-Y by thousands.

 

[Kalvaer]

Once you know where something is and with practice you can point directly at it.

I wanted to buy myself a RDF but then one night my wife and I were messing around and I found out an AWESOME little trick.

We have a 20 mWgreen laser pointer (which if you dont know is a great tool to have when you want to show other people where things are in the sky as well as helping you find something on a star chart)and while we where viewing I took the laser and placed it behind the optical finder. Of course it shone straight through but it was now pointing exactly where the scope was focused on.

So now instead of the RDF, we just use the laser and it works like a charm, Plus it shows other people exactly where you are viewing. You dont have to star hop or anything anymore like this. All you need to know is where the star or what ever you are looking for is located.

 

[Crusader]

That's a nice trick. I've used it myself but prefer the RDF. It's cheaper than a green laser and you don't need to worry about accidentally pointing at aircraft.

 

[Kalvaer]

Depends where you get your Lasers from We paid R350 for ours.

The chance of hitting an aircraft is very minimal unless you a complete idiot in which case I think you deserve spending time in jail. (That and I think the Americans always blow things out of preportion and the risk is not at all as bad as people on forums like CN make out)

 

[Crusader]

Depends where you get your Lasers from We paid R350 for ours.

The chance of hitting an aircraft is very minimal unless you a complete idiot in which case I think you deserve spending time in jail. (That and I think the Americans always blow things out of preportion and the risk is not at all as bad as people on forums like CN make out)

Mine was around R400. I know the laser incidents are totally blown out of proportion most of the time, still there's quite a few planes flying over my location and it's not always easy to spot them at night. I'd rather not take the chance of inadvertently pointing at them while viewing through the scope.

 

[dappled]

er, um, so do i need to not point my red dot finder at planes? or is that not a laser?

 

[Crusader]

er, um, so do i need to not point my red dot finder at planes? or is that not a laser?

No, that is for a green laser pointer. The laser disperses the further it gets and could *possibly* startle a pilot. The red dot finder only reflects the small red led so nobody but you will see it.

 

[Roundhouse]

Is that Jupiter next to the moon tonight?

 

[dappled]

yep that's jupiter... looks like it's on course to eclipse the moon actually...?

 

[Crusader]

Is that Jupiter next to the moon tonight?

100 points to the winner!

Yes, that's indeed Jupiter. It's about 3° from the Moon at the moment.

 

[dappled]

Nah, sorry, too bad it is not

 

[Crusader]

Nah, sorry, too bad it is not

Nope, it's not. And I think the word you were looking for would be occultation. That's when one object is hidden by another. Obviously it's more likely that the Moon will occult Jupiter than the other way round, but that's not going to happen.