September is for many amateur astronomers the best month of the year - the sky is dark and the climate pleasant. It’s now you can stand up for hours at your telescope and let yourself be fascinated by the wonders of the heavens.
On September 14, Neptune is in opposition, i.e. Earth is right between Neptune and the Sun. This means that Neptune is at its closest to Earth and also fully illuminated (compare full moon). The days around the opposition are the best days to observe and photograph the outer planets.
Planet Neptune is not among the most observed objects by amateur astronomers. Despite its huge size (57 Earth would be housed inside Neptune), its distance from Earth makes it so faint that it cannot be seen by the naked eye. To watch Neptune, you need a telescope or a big spotting scope.
Neptune in Aquarius before midnight in mid-September 2021 (the red "cross").
It was not until 1846 that astronomer Johann Gottfried Galle was able to observe the planet, after its existence had been predicted after mechanical calculations by the French mathematician Urbain Le Verrier.
However, it would be until August 25, 1989, before Neptune got its big "breakthrough": It was when the American space probe Voyager2 past by Neptune and took the stunning photographs, that the planet became interesting to a wider public. Among other things, it was discovered that Neptune may have large storms in the upper atmosphere. But unlike Jupiter's Great Red Spot, Neptune's Great Dark Spot has a much shorter lifespan - these large storms seem to come and go every few years.
With an amateur telescope, there is no chance to see any details of Neptune. However, it is possible to see that it is a planet; that the celestial body has a distribution and is not just a shining dot (as a star appears in a telescope). On the previous page there is a star map showing that Neptune can be observed in the constellation Aquarius in September, where it is in the south, barely 25 degrees above the horizon before midnight.
Also note that the planets Jupiter and Saturn are well observable along the eclipse. Many telescopes are nowadays computer controlled and then it is easy to just select "Neptune" from the planet menu and let the telescope do the work.
Finding Neptune using a star map is more difficult; the telescope's inventor Galileo Galilei, for example, was mistaken and took Neptune for a star when he observed it in the 17th century. But there's a difference - with the star map on the previous page, you know where Neptune is and that it is a planet. With a little patience, you will find it even without computer control.
Feel free to use a planetarium program, such as Stellarium, to zoom in on the area around Neptune, so you can navigate between the stars (star hopping, as it is called).
If you have a digital system camera and a telescope, in fact, it is not so difficult to photograph Neptune and thus bring out its blue color. You will then need a telescope with an equatorial mount (which can compensate for the rotation of the Earth), a photo adapter with a T-ring and a high-magnifying eyepiece (preferably with a Barlow lens). Read more in the manual for your telescope and google to see how others have done.
If you manage to photograph Neptune; feel free to share and send an email to Focus Nordic. It may then be published in an upcoming Astroinfo.
The map is made with the free planetarium program Stellarium.
Text: Claes Tunälv