Astronomy FAQs

 

What can I see with my telescope?
Astronomically, you can see the Moon, the Sun if correctly filtered, all of the planets except perhaps Pluto, some surface details on Mars, Jupiter and Saturn, multiple stars, globular and open clusters, bright nebulae, galaxies and nearby galaxy clusters. Terrestrially, there are wildlife, sports, etc., but remember that daytime viewing is often over areas which may radiate heat so that very distant subjects may shimmer.

Will I see objects as they appear in photographs?
Yes and no. Bright objects like the Moon, some planets and some star clusters will show colours and features just like photographs, but faint objects are more difficult. The eye is not sensitive enough to detect colour at low light levels so even bright nebulae appear as shades of gray in small telescopes. Colour films can be exposed long enough to collect light across the visible spectrum so photographs show colours than you don't see visually.

How much power does my telescope have?
A telescope has three types of power and they are measured against the performance of a normal human eye. They are magnifying power, light gathering power and resolving power. All three are important but the most important is resolving power. The longer the focal length of a telescope, the more a particular eyepiece will magnify the image. However, there is a practical magnification limit of 2x per mm of telescope aperture. Using an eyepiece which gives a magnification beyond that limit is normally of little use. The amount of light that a telescope can gather depends on size of the aperture and the more light that can be gathered, the better the resolution. What you will see through your telescope will then depend on these three powers. For example, compared to the human eye, and using the 2x per mm rule, a 150mm aperture telescope will have a maximum practical magnifying power of 300x, a light gathering power of 600x and a resolving power of 0.8 arc-seconds.

What is the advantage of a large aperture telescope?
The larger the aperture, the higher the practical magnification limit. Since more light is collected and brought to focus by a larger aperture telescope, fainter objects can be seen with it than with smaller apertures. Under good seeing conditions when air is not turbulent, a larger aperture objective gives higher resolution, letting you see finer details.

What type of eyepiece should I buy?
For standard eyepieces with a 50 degree apparent field of view, Plössl eyepieces are a good choice if your telescope's focal ratio is f7 or less. For longer focal ratio instruments, simpler eyepieces such as Kellners will be sufficient. Choose eyepiece focal lengths that won't give you a duplicate magnification when a Barlow lens is used. For example, don't get 10mm and 20mm eyepieces with a 2x Barlow.

Which mount should I buy for my telescope?
If your instrument is for land use only, select the alt-azimuth mounting, but if its for astronomical or dual use, the equatorial mounting is the best choice. Make sure that the mounting you select is strong enough to carry the telescope you've chosen. Heavier or longer telescopes need stronger mounts to be stable at high magnifications. When in doubt, over-mount the instrument; choose the mount one size up if you want extra stability.

Should I get a motor drive with my equatorial mount?
A motor drive is necessary for many types of astrophotography, but it is more than just a convenience for visual observation as well. At 200x magnification, the Earth's rotation will move an object out of your field of view in about two seconds. A Right Ascension motor drive will keep an object in the centre of the field where the image is the best without producing the objectionable vibrations experienced with manual tracking. Adding a Declination motor drive and a hand controller allows you to guide for astrophotography.

Should I use colour filters?
Colour filters, which usually thread into the eyepiece barrel, are almost a necessity for viewing planetary detail. By using an appropriate colour, you can highlight a specific planetary feature. This often allows you see two to three times as much detail as in an unfiltered view.

How do I safely transport my telescope?
The telescope can be transported in 2 main parts--telescope tube and mount. Loosen the thumbscrews on the tube rings and remove the telescope tube from the mount. We suggest removing the accessories (finderscope and bracket, and the eyepiece) from the optical tube. Cover the telescope tube and the eyepiece with their caps. It is also convenient to remove the fine-adjustment control cables and counterweight rod/counterweights. Accessory tray should be removed in order to transport with the 3 tripod legs closed. The telescope can be transported in a vehicle without a problem. Padded insulation can prevent scratches on the tube but it is not necessary. The mirrors may go out of collimation after a bumpy ride but collimation can be required after transportation anyway, with or without padding.

How do I store my telescope?
It is unnecessary to separate the optical tube and the mount when storing the telescope. It can be stored in one unit in a clean, dry, and dust-free environment. If it has to be stored outdoors, cover it with a heavy-duty plastic cover to prevent it from getting wet. Make sure that the dust cap for the front of the telescope and the cover for the rear opening are on. Accessories should be stored separately in a box, with all their caps on. Some people do store the reflecting telescope in two parts, leaving the telescope tube up side down on the ground to prevent dust from settling down on the primary mirror. However, it is not proven that it really helps.

How do I find objects in the sky?
The sky is mapped out in a spherical coordinate system similar to the system of Latitude and Longitude on the surface of the Earth. On the imaginary celestial sphere, the coordinates are Declination, which is equivalent to Latitude and measured in degrees, and Right Ascension, which is equivalent to Longitude, but measured in hours. The celestial equator is a projection of the Earth's equator onto the celestial sphere. Because the positions of stars and other distant celestial objects, as plotted on this celestial sphere, change very slowly with time, their listed coordinates and star charts are only updated every fifty years. On the other hand, planets change position so rapidly that their coordinates must be obtained from current astronomy periodicals. The setting circles on your equatorial mount can be aligned with the celestial sphere to aid in finding astronomical objects.

How do I find objects using the setting circles?
Periodicals like "SkyNews", "Sky&Telescope" and "Astronomy" will tell you where the moon and planets are, and the location of all other objects can be found in Star Charts. The quickest way to find objects is to learn the Constellations and use the finderscope, but if the object is too faint you may want to use setting circles. To visit the manuals section, to locate the manual that suits your requirements please click here. (You will need Adobe Acrobat Reader to open the file.)

How do I polar align my telescope?
For visual use, only a rudimentary alignment of the polar axis of your equatorial mount is required. First, the finderscope should already have been aligned to the telescope by centring a distant fixed object in the telescope's field and then adjusting the finderscope with its adjusting screws until the object is at the centre of the crosshairs. The angle of the polar axis should also be set equal to your Latitude. Now, with the mount approximately level, align the telescope parallel to the polar axis (ie set the Declination axis to 90 degrees), and then adjust the polar axis until the star Polaris (the "North star") appears in the centre of the field of your finderscope. This alignment is good enough for visual observation. If you are trying astrophotography, a more accurate alignment is required, and you will need a polarscope if your mount is equipped for it. For longer exposure times, the mount is usually adjusted using a very accurate star-movement measurement technique called "drift alignment."

To visit the manuals section, to locate the manual that suits your requirements please click here.

What is polarscope? How do I use it?
A polarscope is a specialized finderscope which is used to align an equatorial mount with the celestial pole. It is usually mounted in a tube which runs along the RA axis. For northern use, it may have a mark for Polaris, the pole star, which is slightly offset from the North Celestial Pole. It must be rotated so that the offset mark of Polaris is correctly aligned relative to the directino of epsilon-Cassiopeia on a line from it (through Polaris) to Alkaid, the end star on the Big Dipper's handle.

I want to take photographs through my telescope. What do I need?
Most telescopes can be adapted to act as lenses for single lens reflex (SLR) cameras. For the basic technique of "prime focus" photography, all you generally need are a camera body, a T-ring specifically made for your camera body (allows it to connect to a T-thread) and in some cases a combination T-adapter designed for your telescope (supplies the T-thread). This configuration, is fine for terrestrial use, or for the Moon or the correctly filtered Sun, but for fainter astronomical objects you will need to do time exposures using an equatorial mount with a Right Ascension motor to correct for the Earth's rotation. For exposures longer than a few seconds, you should use dual axis motor drives and a hand controller to guide the telescope.

I am observing Jupiter but I only see a shimmering disk. What am I doing wrong?
Astronomers must be patient; you must optimize your observing site and times, as well as your equipment. When you observe the Moon and the planets, and they appear as though water is running over them, you probably have bad "seeing" because you are observing through turbulent air. Always observe objects as high in the sky as possible. Don't observe immediately after sunset and avoid viewing across heat-radiating ground objects such as buildings and parking lots. Let your telescope come to temperature with the surrounding air; sometimes the shimmering is due to "tube currents" within the telescope tube. Try to enhance planetary detail by using colour filters. Optimize all that you can then be patient because good seeing comes and goes.

Harpers Photographic

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