Last night I looked at the moon (just to practice pointing the scope). I also saw Jupiter and its moons. I saw three moons. They were very clear. This morning I took it out again and saw Venus. I could clearly see the bright crescent of Venus' light side. (Venus, just like the moon and earth, has a light and dark side because of the sun.)
Last night I tried again to find Neptune. First I aligned the equatorial mount to the north star. Let me explain why.
Astronomers find stuff using a grid that is like latitude and longitude. The grid is aligned to the earth. The celestial north pole is directly above the earth's north pole (it is very near where Polaris, the "north star" is). The celestial south pole is above the earth's south pole and the celestial equator is -- you guess it -- above the earth's equator. Instead of longitude astronomers use right ascension, or RA. Instead of latitude they use declination or dec (not "declension" as I wrongly told Carolina when we were out the other night. Maybe grammar and astronomy don't mix so well.)
Declination is measured in degrees just like longitude. The equator is zero degrees, the north pole 90 deg and the south pole -90 deg. RA is measured in hours rather than degrees. There are 360 degrees in a circle. There are 24 hours in one day which is one revolution of the earth -- in other words a circle. So one hour equals 360/24 = 15 deg. Astronomers picked hours to make time and position comparisons easier. Time plays an important role in finding celestial objects because the earth is always moving. The zero point for RA is the vernal equinox point. The vernal equinox point is where the sun is at the March equinox, which is the first day of spring and a day where nighttime and daytime are the same length. The earth is tilted compared to our solar system so the solar system plane and the earth's equator plane are not the same. The vernal equinox point is on the intersection of the earth's equatorial plane with the solar system plane. (BTW, most of what I just said also applies to the autumnal equinox, except it is at 12 hours RA.)
The cool thing about an equatorial mount is that is turns on two axis. One axis is RA, the other is declination. The first step in setting up the telescope is to align the telescope mount with the earth so the scope RA axis matches the earth (and celestial) axis. I set up the telescope tripod so it was stable. Then I set the declination to 90 deg. Besides the RA and declination axis, the mount can be turned horizontally and tilted vertically. I used these controls to point the scope at Polaris. I then locked these controls -- they should not change once the scope is aligned. The scopes RA axis was now aligned with the earth's axis.
If the scope has a motor aligning the mount allows the motor to keep the scope synced with the stars. I don't have the motor but aligning it correctly has other uses. Now I could control RA and dec independently. The mount RA and dec axes have angle markings. If they were accurate enough I could use them to find things. I thought maybe I could find Neptune using the marking. I found out last night that they aren't precise enough for that.
Still, aligning the mount helped me a lot. First, stuff is always moving. You find something and pretty soon it leaves. I was using a 25mm eyepiece which gave the scope a field of view (FOV) just over one degree. When I point at something in the center of my eyepiece the edge of the eyepiece is about 1/2 deg away. The earth rotates 15 deg in an hour, or about 1 deg every four minutes, or 1/2 deg in two minutes. That means that once I point the scope, the object will be out of my FOV in about two minutes. Having the mount aligned means I can find the object again just by turning the RA axis. (I take the place of the motor.)
Aligning also helped me search for Neptune. I looked up the position of Neptune for last night. I also looked up the positions of the stars near Neptune. (I used Google Sky and Wikipedia. Google Sky is cool because it shows the RA and dec for where the mouse is pointing.) I used the dec markings to set the scope at approximately the right dec for δ Cap. Then I turned the RA until it looked like I was near δ Cap. I used the sighting scope and found δ Cap. The sighting scope had a wide enough FOV so I could see δ and γ at the same time. I moved down a little and saw κ and ε. I scanned up a little and to try to see 45, 44, and 42 Cap, but the sighting scope could not pick them up. Still I was pretty sure I had found δ and γ Cap. Since γ Cap is about the same dec as ι Cap, I moved the RA right to get to ι Cap. The picture below is from Google Sky. It got compressed in the blog so it's hard to read. Neptune is the big blue ball (just an icon, it's not really that big in the sky). δ Cap is on the middle of the left edge, γ Cap is just right of it. ι Cap is under the red box.
I thought Neptune was pretty near the same RA as ι Cap. When I found ι Cap I locked the RA and moved up with the dec. I never really found Neptune. When I went back inside I looked at Google Sky and decided I had spent my time looking in the red box. I believe I found the star in the lower right corner of the box and didn't stray too far from it. I didn't go back out because I really do need to sleep sometimes.
Now I have practice working the scope on the mount. I have a much better idea of its FOV and how to find stuff with the sighting scope. Maybe tonight I can bag Neptune. Hopefully I'll also have time to see how Uranus looks with it, and maybe Andromeda.
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