Monday, April 30, 2012

Observing Stars and Planets during the daytime

You may be surprised at how many planets and stars you can see during the daytime! You don't need a big or specialized telescope, Although it's particularly easy if your mount has go-to capability. But there are a few things to keep in mind if you want to do this safely.
  • NEVER look at or near the sun unless you are using an appropriate and correctly-fitted filter on the telescope objective. If you're not 100% sure about what you're doing, stick to observing at night.
  • CAP the telescope objective whenever slewing near the Sun; if the scope slews across the sun, heat may damage your telescope. Make sure your cover is secure and won't fall or blow off.
  • ALWAYS keep your finder telescope's objective covered, and cover its eyepiece, too, just to be extra safe. You won't be using your finder anyway. Even safer is to remove it from your telescope.
  • DON'T do slow search slews near the sun while looking through the eyepiece. If even a small portion of the Sun's disk slides through the field of view for a tiny moment eye damage would result!
If you get the feeling from all this that it's not particularly safe to look near the sun, GOOD.

Now, assuming you're not completely scared out of trying this, here's how to spot daytime stars.

If possible, the night before do a good polar alignment followed by a multi-star alignment so that its go-to is ready. Some mounts let you retain the go-to information with a Hibernate mode. If your mount has that feature, use it.  The next day, awaken your mount from Hibernation.

Use the go-to to find the brightest object other than the Sun. This may be Venus or the Moon; both are easy to see during the daytime when far enough in angle from the Sun. "Sync" your mount to the object if possible. Syncing is useful for doing go-tos to targets near the synced object. For example if you have synced to Venus in Taurus, you might select Rigel, Capella, or Betelgeuse to look at.

Once you've gone to the target star, you may have to hunt a bit. Use a low-power eyepiece and scan outward from the center of the field of view. I use a slow spiral when searching. Don't bother using averted vision, as it's ineffective with the daytime brightness. Remember that you're looking for a tiny sparkle of light, not a glaring bright star.

Your luck will be best when you look farthest from the Sun, when the Sun is low in the sky, and when your target star is well above the horizon. The larger your telescope's objective, the dimmer the stars you'll be able to see. Even with a small telescope there's a lot you can see. If the sky is hazy or there's a thin layer of clouds, you will probably be limited to only the brightest sky objects.

Here's one days observations I made using a 72 mm ED refractor on a CGEM mount. Most of the time I was using a 12.5 mm or 9 mm eyepiece, giving magnifications of  about 35X and 48X. I tried a variety of color filters, but only a yellow #15 seemed to help.

Planets I observed:
  1. Venus was my starting point and on this day was a brilliant crescent.
  2. Jupiter (-2.00) was a ghostly disk
  3. Mars (-0.3): Much easier than Jupiter at -2.00, a distinctly red disk.
I tried Mercury, but the the sky was too bright.

Stars I observed (and their magnitudes):
  1. Capella (0.08) was easily seen
  2. Betelgeuse (0.45) was easy when it had risen high enough, and showed distinct color
  3. Aldebaran (0.87), fairly easy and had a distinct reddish tint
  4. Procyon (0.4) not too bad
  5. Pollux (1.16) easy
  6. Castor (2.0 and 2.9) This double was split cleanly with a 6mm (72X) eyepiece and #15 yellow filter. The reason I could see the faint companion was that I knew exactly where to look, which makes a tremendous difference.
  7. Alhena (1.93) no problem
  8. Sirius (-1.44) Quite easy despite being low in the sky.
  9. Rigel (0.18) fairly easy.
  10. The three belt stars of Orion, from east to west (Alnitak, 1.74; Alnilam, 1.69; Mintaka, 2.25) only Mintaka was moderately difficult
  11. Saiph (2.07), the SE foot of Orion. Easy
  12. Bellatrix (1.64), the NW shoulder of Orion. Also easy. With Betelgeuse, Saiph, and the belt stars, it's easy to see all the the "signature stars" of Orion during the daytime!
  13. Regulus (1.36) easy
  14. Algieba (2.01) fairly easy
  15. Dubhe (1.81) Very clear.
  16. Merak (2.34): Yes.
Not bad for a late morning and mid-afternoon's work. Unfortunately, clouds rolled in and I didn't get to do more during the late afternoon when more stars would have certainly been visible.
This shows how you can see stars down to almost 3rd magnitude during the daytime with a small telescope. If your telescope is larger, you can probably do better than I did.

Try this out for yourself and let me know how you did. You might be surprised at how pretty stars are during the daytime!

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