Night Sky July 2005
The summer night sky is filled with magnificent bright stars. With the warm nights, this is prime time for observing. If you are interested in learning more about our beautiful night sky, I will be giving a talk at the Placitas Library at 7:00 p.m. on July 7. I hope to see you there.
If you are getting a bit more serious about astronomy, summer is a great time to have a telescope. Most beginning astronomers are not sure what is really important when buying a telescope. Well, here are a few tips.
There are two basic types of telescopes. The first is the refractor. It uses lenses to focus the light. You will recognize this type if you can see a lens in the end of the telescope. The second type is the reflector. It uses curved mirrors to focus the light. It will not have a lens in the end.
If you are buying a refractor, it is better to have achromatic lenses (you can purchase telescopes that do not use achromatic lenses). An achromatic lens combines a concave and a convex lens to bend light. This ensures that most colors of light focus at the same point. These telescopes have sharp views and good contrast, but they are very expensive for their aperture. For $500, the largest refractor you could get would be about three inches, which would be adequate for planetary viewing but would be almost useless for deep-space viewing. Also, these telescopes tend to give you blue halos around the stars. Non-achromatic refractors use one or two convex lenses to focus light. They tend to blur images because they do not focus all colors of light in the same spot which gives them distorted views. These are your typical department-store refractors. They are very cheap in price and almost useless for astronomy. Non-achromatic refractors are best avoided.
Newtonian reflector telescopes give you the most apertures for the dollar. A Newtonian reflector uses mirrors to reflect and focus light. Newtonian reflectors give very sharp views with almost as much contrast as an achromatic reflector. These telescopes are good for any astronomical use you may have for them. A reflector is the most cost-effective telescope you can buy.
Try and stay away from inexpensive department-store telescopes. They are usually inexpensive for a reason. So, here are some suggestions:
- If a telescope looks much too complicated to use, it more than likely is.
- If a telescope's view jiggles in the store, it will do so when you try it on the sky. Get a good, strong, steady mount.
- Stay away from the telescope that claims lots of power or magnification. High magnifications aren't really useful, because the atmosphere is unsteady from your backyard and high power magnifies the twinkling effect. Higher magnifications also make it hard to find and track an object in the sky. Most observing from the backyard will be done with magnifications between fifty and 125. This is more than enough to let you see great views of craters on the Moon, the rings of Saturn, and the moons of Jupiter. A good rule-of-thumb is to limit your magnification to fifty times the aperture size in inches.
- Pay attention to aperture. Aperture is the diameter of the front lens or main mirror used for collecting light. The bigger the mirror or lens (aperture), the more light is collected and the brighter the images will be in the eyepiece. Brighter images allow you to see fainter objects in the sky. Just be warned: the larger the aperture, the larger the telescope, the more difficult it is to move out to the driveway or drag out to the backyard. It may not even fit easily inside your car.
- A simple, wiggle-free altazimuth mount is better than a "scientific looking" but flimsy equatorial mount.
- Look for a telescope that uses eyepieces with the standard 1.25-inch barrel diameter. Otherwise, eyepieces may be hard to find or extremely expensive.
- Plan to spend $400 or more to improve your chance of avoiding junk. Don't let that scare you away, though! It really is worth it. If you just can't swing that much money, I would recommend buying a nice pair of binoculars and a couple of star-chart books. It's a great way of getting started and you can start saving the pennies for a future purchase of a scope.
For those just starting out, consider a 2.5-to-3-inch refractor or a 4-to-6-inch reflector.
I hope this helps answer some questions about telescopes. Now, go outside and enjoy the summer night sky.
The Moon and Planets
- Early in July, Mercury and Venus are side by side, but they begin to part ways later in the month. Look for both low on the west-northwestern horizon just after sunset. You will find a spectacular grouping of these two planets with the Moon on July 7 and 6. Mercury reaches is highest point in the evening sky on July 9.
- Earth reaches aphelion, the farthest point from the sun in its orbit, on July 5. We will be 3.1 million miles farther away from the Sun that we were in January.
- Mars is just peeking above the eastern horizon as dawn breaks. Mars and the Moon form a close grouping on July 27.
- Jupiter is high in the southwest at sunset. The Moon joins Jupiter on July 13.
- Saturn has moved into the Sun's glare and will be missing from the night sky this month.
- The Moon will be new on the July 6 and full on July 21. July's full moon goes by several names: the Full Buck Moon, for the time of the year buck deer sprout new antlers; Full Thunder Moon, for the frequent summer thunderstorms; and Half Hay Moon. Tides will be high this month since the full moon coincides with the Moon's orbital perigee. This is the closest approach in the Moon's orbit to Earth, a mere 221,928 miles above our heads.
- Many unusual types of shooting stars will grace our night sky on July 4.
The Red Planet is about to be spectacular. This month and next, Earth is catching up with Mars in an encounter that will culminate in the closest approach between the two planets in recorded history. The next time Mars may come this close is in 2287. Due to the way Jupiter's gravity tugs on Mars and perturbs its orbit, astronomers can only be certain that Mars has not come this close to Earth in the last 5,000 years, but it may be as long as 60,000 years before it happens again.
The encounter will culminate on August 27 when Mars comes to within 34,649,589 miles of Earth and will be (next to the moon) the brightest object in the night sky. It will attain a magnitude of -2.9 and will appear 25.11 arc seconds wide, at a modest 75-power magnification
Mars will look as large as the full moon to the naked eye making it easy to spot. At the beginning of August, it will rise in the east at 10:00 p.m. and reach its azimuth at about 3:00 a.m.
By the end of August when the two planets are closest, Mars will rise at nightfall and reach its highest point in the sky at 12:30 a.m. The sight will be something that no human being has seen in recorded history.