Comet NEOWISE is making a great show right now. It passed closest to the sun on July 3rd and is now slowly moving away from the sun. This means we have to observe the comet very low in the sky. This is absolutely normal for comets but it put some demands on us observers.
1. Find an observation spot with a free horizon in the comets direction
Find the comet position for the planned observation time and find the Azimuth direction. TheSkylive.com is fine for this kind of planning. Using the Azimuth direction look at Google maps and find an observation spot where you have a free view in that direction. Google Streetview can help estimating the local horizon.
2. Bring your mount and telescope to the observation spot
Most telescopes and mounts can be transported to the observation spot but it is an advantage to have a setup that is easy to transport and setup.
3. Setting up and aligning
If it is in the evening twilight it is important to get started as soon as possible as the comet is setting soon after the sun.
Setting up an Alt/Az mount in daylight is easy. Depending on the mount software there are different possibilities. Here is how I do it with the Panther Mount.
Set up the mount. No leveling or polar alignment needed.
- Align on the sun before it sets.
- Point to the sun (Always with a solar filter on) and make 1st alignment. Often this will be precise enough as the comet is in the same area.
- To improve the alignment you can wait 15 minutes and align on the sun again as 2nd alignment object. This will give a precise alignment.
- Based on the first solar alignment it is possible to slew to a bright star (visible in daylight in the telescope) and use that as alignment object.
- Align on bright star or planet
- As soon as it is dark enough align on the first visible stars
If you often return to the same observation place read the article about alignment based on terrestrial objects.
Polar aligned mount
Setting up a polar aligned mount during the day is difficult. All precise alignment principles needs stars to be visible. Here is what is possible to do:
- Set up the mount head and level it precisely
- Set the polar axis height on the mount to match your latitude
- Using a compass point the polar axis towards north
- When it is dark enough tweak the polar alignment as needed
4. Observing the Comet low in the sky
I observed and imaged Comet c/2020 F3 NEOWISE yesterday just 5 degrees above the horizon. As it was close to the sun the sky was not dark and the sky was covered with Noctilucent Clouds making the background extremely bright. Still I was able to see a nice split tail about 0.5 degrees long. The seeing never allowed for high power observations of the head. In the coming days I hope to have a chance to observe it in details.
Here is how I will observe the comet in the evening twilight
- Having aligned the mount before sunset I will make a goto the comet position and watch when it will start to appear:
- In the brightest twilight I will observe the comet head at high power. The comet has the highest altitude at this time so the seeing will be best. If the comet head is bright you might try some lucky imaging (planetary technique) and see if you can catch jets coming out from the nucleus.
- As it gets darker start to observe for fainter details in the coma
- At some point the trade-off between comet altitude and darkness will give the best overall view of the comet. A good moment to take that wonderful comet portrait.
- When the comet head gets close to the horizon try to observe the full length of the tail. A good time to image the the comet wide field.
And the morning twilight
The morning twilight is much easier to handle. You have all night to setup and prepare. BUT it is 3 am….