At a minimum, a long shaft drill bit is needed. Frys has 18, 36, and 72 inch long 3/8" (9.525 mm) and 18 by 1/2 inch (12.7 mm) drill bits intended for stereo/security/network/hvac system installers.

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Then you put the reference face against the surface to drill, and put a long auger through it to get the hole started. In your case, with such a deep hole to drill, you can remove the guide once you are a few inches in. I like using an auger bit with an impact driver, even though it is loud and requires adapters, because the combination is easy to control and makes steady progress.

Use a good quality wood auger selected for correct diam & of sufficient length. Then select the slowest drill you can find/borrow. It's easy to start exactly on center but even at slow RPM the bit will rapidly advance & provide little opportunity to correct if the auger wanders off course. The best way practically speaking to keep the auger true & square to the surface being drilled is to have two observers assist, each one checks the angle from 90 degrees apart & helps with alignment. If you mess up you will have to start again or correct with a chisel, so a practice run is almost essential.

At least 3 guides are needed to counteract sideways forces you or the drill would tend to make. As for technique, fast rotation and slow drill movement with low forces is the best way to make the bit not wander. Adding an extra guide with a bore that is bit tip width which rests against the work piece would greatly help consistently start the bore in a consistent place.

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You could duct tape a level to the side of your drill. Use a plumb to confirm that the level is parallel to the bit. Drill slow with a thin bit first; focus on keeping the drill level instead of getting through the wood.

For your problem, I would obtain one of these at least 36 inches long and build a jig (a drill guide on steroids) to hold it. The shaft on my 72 by 3/8 inch bit is 3/16 inches (4.76 mm) diameter and while it is not firmly rigid, it is not highly flexible either.

While a drill press (the most popular suggestion so far) might seem to be the ideal tool for this, it is quite difficult to find one which has a stroke of more than 3.5 inches. Even by reversing the work piece, that leaves more than 2 inches not bored with little assurance that the holes from each side are co-linear.

This method can be handy if the wood is too big to easily balance on the drill press, or if you don't have a drill press, but know a friend with one who could make you a guide block. Use a thick scrap chunk of hardwood with the true face (the one you choose to be your reference) face down on the drill press, then drill a guide hole with the same diameter as your final hole. The thicker the wood, the more accurate it will be as a guide.

I built a drill guide jig for this. The basic concept is to secure a piece of pipe with an inside diameter just slightly larger than the auger bit. My use case was a timber frame outdoor kitchen with exposed joinery. Peg holes were 1" diameter going through 8" timbers. The jig was time-consuming to use but very accurate. Pics and YouTube video below.

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I drilled a bunch of dog holes in a workbench recently using a wooden guide block that I made in a drill press, and it worked really well.

A drill press is probably good enough. However, I would drill from both ends with a pilot bit and then finish with the size required.

Lay the disk down and line up the drill through the middle. The reflection of the bit /shank should be in-line with the bit/shank that you can see directly. Look from above and beside to make sure its in line in two directions.

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I have had good luck with auger bits rather than twist or paddle bits for straight holes. Once you get it started straight, it should take care of staying straight for you.

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Nine inches is quite a distance. Even w a 1/4" pilot drill you'll end up getting some wandering of the hole at increasing depth. Going straight to a half inch is likely to bog down your drill press or lathe. When you need precision, for example when making long rollers that must be symmetric around a central drive shaft, the usual practice is to start w two pieces of wood, route out a centered channel through each, glue the pieces together, drill hole to final size, and turn the result on a lathe until everything is nice and even. This book may be of use in your particular case: Deep Hole Drilling

I have the opposite idea. Move the wood to be drilled to the drill bit! Start with a straight piece of shutterboard and set up the drill on a block using the level to ensure the drill bit is level/horizontal. Then mark on the board two lines exactly parallel to the drill bit and the same size as the section you wish to drill. Now screw 2 fairly deep guides on the outside these lines, creating a channel so the section fits fairly tightly into the gap. Now switch the drill on and push the section towards the drill. With the guides preventing the section from moving to either side all one needs to do is hold the section down and at the same time pushing slowly to feed it into the drill