# Is it possible to do planet observation during the day?

Keep in mind I'm just a newbie. So.... I have a new Newtonian telescope. It has 150mm opening and 1400mm Focal Distance on top of an equatorial mount. I have 25 and 10 mm eyepieces... and a 2x Barlow. I sat down to do observation yesterday and was able to see Saturn and Jupiter (warming up for the alignment on the 21th). Now, I did notice that as they sank closer to the horizon, the effect of the atmosphere was more apparent (and they were less sharp) so I'd like to see if it is possible to see them earlier when they are higher in the sky to try to minimize the effect of the atmosphere... but that might mean to watch them when the sun hasn't set yet. I know that we can't see them with the naked eye when it is daytime but given that the telescope is letting a lot more light in, then it should be possible to see them if I point in the right direction? I intend to use the sun to get RA/DEC alignment (using the telescope shadow, don't intent to look at the sun with the telescope.... yet! :-D) so that then I can point the telescope in the direction of the planets (and I am using Stellarium on my Debian box to get the numbers and stuff).

• I've seen Mercury and Venus on blue skies, but I haven't tried Jupiter and Saturn. Dylan O'Donnell made a video about taking a photo of Jupiter during the day, youtu.be/EtE87WzYieY I assume you know to never point a telescope (without a solar filter) at the sun and are using an indirect method like: skyandtelescope.org/astronomy-resources/… Dec 13 '20 at 15:42
• To align it? Was thinking of using its shadow, actually, in order to align it. Don't intent to look at the sun with the telescope.... and thanks for the warning, anyway. Dec 13 '20 at 15:57
• I would suggest that if you are newish at this then it would be better to get the basic nighttime technique well learned and practiced before attempting anything too advanced. Just night astronomy is difficult enough to do consistently well for most people. Dec 13 '20 at 18:15
• I’ve been told a few times that Venus is bright enough to be seen naked eye during the day on clear skies, if you know exactly where to look. But have to have good eyesight and I’m sure it has to hit the fovea spot on. I’ve tried a few times without success though. Dec 15 '20 at 17:46
• I don’t think the scope’s shadow is anywhere near precise enough. If I were you I would try to get a “solar finder” such as the TeleView Sol-Searcher. Make sure you have a way to attach it to your tube without sacrificing the (regular) finder as you’re going to need it to find the planets. But aligning the sun finder itself might be tricky without looking at the sun via a proper (aperture) solar filter and I would be hesitant to do that alone if it was my first time without in-person guidance for safety. And I worry there might not be enough time to procure it before the event. Dec 15 '20 at 18:10

Jupiter can be seen during the day.

This image is by Philip Crude. Philip is an experienced astro-photographer. On his webpage http://www.billionplanetsquest.com/p/planets.html he gives details of the equipment and settings used:

This image was captured through my [i.e., Philip Crude's] Celestron CGEM-800 using a ZWO ASI120MC camera at prime focus. Resolution 640 x 480, 35fps best of 900, Brightness @ 1, Gamma @ 48, Gain @ 11. The image was acquistioned with SharpCap and processed with RegiStax and CS6.

Philip also tweeted the image here.

The main difficulty is pointing the telescope in the right direction, as you won't be able to align it against the background of stars, so you need to predict the position and point the telescope accordingly.

• Suggested edit : "The image was acquistioned with SharpCap and processed with RegiStax and CS6" rather than your last two lines - it's a direct quote from the second site you linked to about that image. Dec 13 '20 at 18:21
• That edit with an out of context quote from Philips website made it look as if I was claiming to have taken the picture, which I wasn't. So i've deleted all the metainformation about how the image was captured It wasn't really relevant, I just hoped to indicate to the OP the sort of equipment that was used. If you want to see then follow the links. Dec 14 '20 at 1:08
• I edited Philips technical information back in because I think it is of particular interest in the context of this question, and we are encouraged to copy relevant parts of pages we link to. I edited the answer to make it clearer that it wasn't your photo, James. Dec 15 '20 at 10:08
• Also, I'm compelled to add that I'm in awe of that picture. Stunning. Dec 15 '20 at 10:09
• Notably caught Io in that shot as well. So if your next question was "Is it possible to observe another planet's moons during the day?", well... Dec 15 '20 at 19:11

When looking at an object through Earth's atmosphere, we know that it

• removes some light multiplicatively due to absorption and scattering
• contributes some light additively due to things like scattered light from other sky objects (e.g Moon and now Sun) and skyglow.

During the daytime you can dramatically improve your contrast by rejecting blue and green light first, thereby removing much of the light from the daytime Diffuse sky radiation which is of course quite intense at shorter wavelengths due to the $$1 / \lambda^4$$ behavior of Rayleigh scattering.

You can do this by either

1. using a digital electronic eyepiece i.e. a CCD or CMOS camera receiving an image from the telescope then displaying it on some electronic display (either a phone or a true digital electronic eyepiece)
2. using a red filter that removes blue and green light, and perhaps an opaque cloth over your head to make your viewing environment darker if necessary.

Here's an analysis of the tweeted image. I've first converted to a png so that it's simpler to read in Python without having to instal PIL/Pillow. The three peaks in the histogram show the dominant uniform sky value with relative rgb values of 0.19, 0.43 and 0.88.

This is not an accurate description your results using an electronic eyepiece or a blue filter, but it does illustrate how these can help.

Image as png: https://i.stack.imgur.com/tiGQD.png converted from this JPEG-containing tweet by Philip Cruden

import numpy as np
import matplotlib.pyplot as plt

rgb = np.moveaxis(img, 2, 0)
histograms = [np.histogram(thing, bins=256) for thing in rgb]

plt.figure()

plt.subplot(2, 2, 1)
colors = 'rgb'
for (a, b), color in zip(histograms, colors):

plt.plot(b[1:], a, color=color)

for i, (im, color) in enumerate(zip(rgb, colors)):

plt.subplot(2, 2, i+2)
mean = str(round(im.mean(), 2))
plt.title('color = ' + color + ' mean = ' + mean)
plt.imshow(im, vmin=0, vmax=1, cmap='gray')
trace = 400 - 380 * im[215]
plt.plot(trace, '-r')
plt.plot(np.zeros_like(trace), '-k')

plt.show()

• The kind of stuff I hope I'm able to.understand in due time. Dec 14 '20 at 1:22

# Moon as reference point

With a bit of patience, you can wait until the Moon is:

• not too close to the Sun
• close to the planet you would like to watch

If the angular separation between the Moon and the planet is less than ~5°, you can use Stellarium to know in which direction you should move your telescope. You can use the terminator as a reference line, and the Moon diameter (~0.5°) to know how far the planet should be. If the planet is further away, it might be too hard to use the Moon as reference.

First quarter moon (🌓) will be helpful if the planets are in the sky before sunset, last quarter moon (🌗) will be helpful if the planets are in the sky after sunrise.

You might have to try different eyepieces :

• if the magnification is too high, you might miss the planet
• if the magnification is too low, the sky will be really bright and the planet might not be visible
• the planet is probably not bright enough in the finder, compared to the background sky

With this method, I've seen Venus, Mars, Jupiter, Saturn while the sun was still in the sky, with a simple Dobsonian. No need for GOTO or equatorial mount.

I've also watched Mercury during the day, by using Venus as a reference point.

You could try next week, 23rd of December, at around 15:00. The sun will be SW, the moon and Mars will be around SSE (as seen from the northern hemisphere). Mars will be a bit further away than 5° from the Moon, but it might still be doable.

# Stellarium tips

• Click on the Moon
• Track the Moon (Space)
• Hide the ground (G)
• Hide the atmosphere (A
• Equatorial mount (Ctrl + M)
• Equatorial grid (E)
• Press L repeatedly to advance in time
• Press K to stop when the Moon is close to a planet, preferably during a quarter moon.
• Show the ground and atmosphere again, to see when the Moon and planets are high in the sky.
• +1 This is an excellent answer and great advice!
– uhoh
Dec 15 '20 at 0:07

It is possible, and under certain conditions, you don't even need a telescope at all!

Around noon on December 3, 2018 I saw Venus with the naked eye. The moon was invaluable for finding. My cell phone camera even (barely) picked up Venus. It is only about 100 pixels in this jpg, but it's there at the center of the indicated circle.

• What would be the ideal conditions that I should be longing for? I guess one of them is that humidity be as low as possible, right? What are acceptable values? What else should I consider? Dec 14 '20 at 19:29
• @eftshift0 Yes, cool dry air is better than warm moist air. The humidity itself isn't a problem, it's the variations in density / refractive index due to temperature & humidity that make the optical path wobbly. Dec 14 '20 at 20:58
• It's kind of surreal to see Venus with the naked eye in the middle of the day. I managed to spot it at every hour of the day a few years ago, when it was bright & close to the Moon. It's also possible (with practice) to see it without using the Moon as a reference, but the Moon certainly does make it easier. You just need to be in a familiar location where you can use ground-based landmarks (like treetops or points on a nearby roof). Dec 14 '20 at 21:11
• Beautiful cell phone image! I cropped and plotted the blue channel only (as discussed here) between 0.55 and 0.75 and pulled out Venus more clearly using plt.imsave('hey!.png', rgb[0], vmin=0.55, vmax=0.75, cmap='gray') This puts the sky level close to zero and accentuates the familliar JPEG artifacts. Did you have to work hard to get the phone to focus at infinity? i.stack.imgur.com/wK78G.png
– uhoh
Dec 15 '20 at 0:22
• @PM2Ring: It's also really impressive how easy it is to miss Venus during the day. Once you see it, it's really clear, but as soon as you look one degree away, it disappears. Dec 15 '20 at 7:43

Bear in mind an equatorial mount only works well when properly aligned. If your scope has GOTO you should enter the name of the planet (if it's in the database) and use the lowest power you have, since that will give you a larger area of sky, thus a greater chance your target will be visible there.