Star Atlas

wAi_kiT · Post by **wAi_kiT** » Wed Sep 06, 2006 12:28 am

I've got myself a Norton's Star Atlas, 20th Edition. What I see inside are charts of stars, and lots of value... Can someone teach me how to read and use the star atlas? Thanks...

Post by **weixing** » Wed Sep 06, 2006 12:40 am

Hi,
I don't have Norton's Star Atlas, so don't know their legend (the star chart will usually have a legend explaination section). But below are some common legend:
1) Bigger "stars", mean brighter stars
2) those value along the edge of the star chart that show: 01h, 02h, 03h... 23h is the RA coordinate
3) those value along the other edge of the star chart that show +/-0 to +/-90 is DEC coordinate... celestial South pole is -90 and celestial North pole is +90.
3) Those star that got a small line across them are double star,
4) Those star that got circle around them are variable star,
5) a circle with a cross in it are usually globular cluster,
6) a dotted circle are usually open cluster,
7) an oval shape are usually galaxy,
8) those irregular shape usually represent nebula, and
9) those small circle with four small straight line outside the circle are usually planetary nebula.

Hope it help.

Have a nice day.

wAi_kiT · Post by **wAi_kiT** » Wed Sep 06, 2006 12:41 am

Well, i'm not too sure of how to use the star charts. But I'm using programmes like Starry Night.

Post by **weixing** » Wed Sep 06, 2006 12:47 am

Hi,
You know how to use a normal map?? If yes, you'll know how to use a star chart. Remember, we put on the ground when using normal map, so when using the star char (map of the sky), you put in "on" the sky.

Have a nice day.

wAi_kiT · Post by **wAi_kiT** » Wed Sep 06, 2006 12:52 am

Haha... But the problem lies with... On the star chart, you see lots of stars, bright, and dim ones. When you look at the star chart, uncertainty comes in. You don't know whether the star you point on the chart is the correct star you're looking at in the sky.

The other question is, does our location also affects the star chart?

Post by **weixing** » Wed Sep 06, 2006 1:03 am

Hi,

The other question is, does our location also affects the star chart?

Yes, but in Singapore... it is easy... the center line which indicate the 0 dec, is basically overhead. Point the north end towards north and you are done... use your software as a guide and to see when you can see which constellation and use that star chart with that constellation on it.

In Singapore, we can only see the bright stars only which is around 4th magnitude and above.

Have a nice day.

wAi_kiT · Post by **wAi_kiT** » Wed Sep 06, 2006 1:15 am

Oh ok... Got another question for you... The 0 dec thing is solved, but at the bottom, the longtitude are being classified in terms of hours... So locally, whats the "hour"?

wAi_kiT · Post by **wAi_kiT** » Wed Sep 06, 2006 1:26 am

Hmmm... So our RA value is...?

Post by **weixing** » Wed Sep 06, 2006 1:37 am

Hi,

Hmmm... So our RA value is...?

RA is basically the Longitude of the sky... not ours.

Give you an example on how the RA is use:
You saw a Star in the east, 40 degree above the ground at 10pm. You look at the star chart and identify that star as Star A and has an RA of 01h 00min 00sec and DEC of +10 degree.

Then you saw another star, Star B, on the Star chart with an RA of 02h 00min 00sec and DEC of +10 degree. The RA different between them is 1 hour, which mean a hour later, Star B will move to the current position of Star A (both have same DEC).

So, at 11pm, you saw Star B at the position where Star A used to be a hour ago.

1 hour is around 15 degree. So the whole sky got 24hour. Get it??

Hope my explaination is good enough...

Have a nice day.

wAi_kiT · Post by **wAi_kiT** » Wed Sep 06, 2006 1:45 am

Oh ok... So the RA value so-called states the "direction" of the object, as in it replaces the north south east west directions ya? So 0hours means its due north? And as you mentioned earlier, 0 degrees is the sky exactly overhead, meaning perpendicular to the ground. So does it means that a star 30degrees from due north is the same as RA 00hr 00min 00sec and DEC of +60 degrees??