Astronomy with a cellphone — take a picture of a planet over 4 billion km (2.6 billion miles) away!!!
I’ve resorted to a click-baity headline for this article about Neptune. No, your cellphone picture won’t look like this one unless you strap it to a space probe and send it out to Neptune:
You’ll need some awful big batteries to go with the cellphone as it takes about 8 years to get there with space probe. Even at the speed of light we see Neptune as it was about 4 hours before you looked. Or if you want to know what it looks like now you have to wait 4 hours.
Currently (early Sep. 2022) Neptune is above the horizon after dark and reasonably high above the horizon for observing by 11PM. Neptune is too faint to spot without using a telescope. Larger binoculars from a very dark site might work but it may be difficult to pick it out from the surrounding stars. A telescope at higher magnification will show Neptune as a small blue disk.
It’s also pretty easy right now (early fall 2022) to know where to aim your cellphone, Neptune is about 15 degrees to the west of Jupiter. If you put Jupiter to left side of the photo you’ll get Neptune too. If you’re reading this article at some time in the future use planetarium software to figure out where Neptune is.
If you don’t have a telescope handy, but have your cell phone that supports astrophotography (see this earlier article) you can use that to see where Neptune is. If you take pictures separated by a few days you can make an animation of its movement like that described for Saturn in this article.
Like Saturn, Neptune is currently exhibiting retrograde motion in the night sky, appearing further to the west each night.
Neptune, being around magnitude 7 (the bigger the number the fainter the object), will be trickier to find. You’ll want to use planetarium software to match up your pictures with the stars and where Neptune is. Stellarium is used in this example.
It can take some practice to get the hang of matching up pictures to a star chart. This is what we call human plate solving versus an automated way.
Since Neptune is faint in these pictures —cloud gods willing — it definitely helps to take pictures on a few different nights. The first two in the animation below are only one night apart and it’s difficult to tell that Neptune has moved. The 3rd frame, taken about 2 weeks later, clearly shows Neptune’s motion. If you have trouble spotting Neptune the sequence repeats with arrows added.
Even though Neptune is just a faint smudge moving across the field you can picture it as this cold (-200° C; -330° F), windy (2200 km/hr; 1300 mi/hr), blue planet that’s almost 4 times Earth’s diameter. That cold temperature means that the trace gasses in its atmosphere exist as ices (i.e. solids, think like ice crystals in clouds in Earth’s atmosphere).
We typify Neptune by the designation Ice Giant. Neptune is less than 20% Hydrogen and Helium by mass, as opposed to Jupiter and Saturn which are over 80% of those two gasses by mass and are termed Gas Giants.
Regardless of naming, you can use your cellphone to see this far off lonely frozen orb make its way across the night sky.
