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Is it possible for an amateur astronomer to visually perceive an exoplanet transit by the change of brightness of the star via observations spaced over time, or is the variation of the brightness too insignificant to be seen?

I have a 70mm scope, but no astrophotography equipment or software to compare data. My question is about really perceiving the brightness variation with our own eyes over time as we see it on variable stars.

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Amateur equipment is good enough. But you cannot detect it with a naked eye.

The change in flux for a passing exoplanet in transit is roughly 1%...2% at most for the larger exoplanets - and it is a gradual change. That's a change you do not notice with the naked eye, but it needs photographic equipment to create a sequence of images which allow analysis of brightness of all seen stars in order to detect the variation in the one interesting one.

With an appropriate camera and stable mount your 70mm telescope will suffice to detect these light changes in a sequence of moderately long-exposure images over the course of a few hours (exposure time a few minutes each).

Many of the professional ground-based exoplanets surveys don't use or didn't use much larger telescopes (e.g. see the HATnet programme). The difference often is more in the grade of automation, the sensitivity of the photographic equipment and automation of data processing pipeline.

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Can exoplanet transits be detected visually with amateur equipment? No. The magnitude change is too small.

With proper equipment, transits can be detected by amateurs. For example, American Association of Variable Star Observers (AAVSO) members are collecting data according to the page Exoplanet Section.

ANNOUNCEMENT: With the launch of TESS (Transiting Exoplanet Survey Satellite), follow-up ground-based observations will be an important part of the TESS process to confirm candidate exoplanets. In particular, such observations will help distinguish false positives from true exoplanet transits. The AAVSO is pleased to announce that it has established a program that will facilitate the participation of its members in this process.

Although small in diameter, I suspect a 70 mm diameter telescope is not entirely out of the realm of possibility. I suspect the main difference is that people that can afford the cameras or other detectors to take the measurements also spend more money on a higher quality telescope.

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Of course transits are observable with telescopes; this is the main method for detecting exoplanets, see Wikipedia's Methods of detecting exoplanets; Transit photometry.

Unfortunately, they can do this only with powerful equipment. The magnitude change varies from 0 to 0.03. This can't be seen with, for example, 700 mm telescope. Thus, 70 mm telescope without equipment isn't powerful enough. With that telescope you can notice around 0.3 magnitude change.

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    $\begingroup$ +1 Where does "With that telescope you can notice around 0.3 magnitude change" come from? Can you cite a source for this? Thanks! $\endgroup$
    – uhoh
    Jan 16 at 0:57
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    $\begingroup$ It comes from my experiences. Of course there are formulas for this, but they are just theoretical. Also, you can detect even change in magnitude 0.1 if it changes in 1 second, but you can't detect change of magnitude 0.5 if it changes in 1 year, so it needn't be so accurate. $\endgroup$
    – User123
    Jan 16 at 9:27
  • $\begingroup$ Cool, thanks! You might enjoy Why do these photometric observations of Betelgeuse look “quantized” in 0.1 magnitude steps? That doesn't mean people can detect 0.1 mag, just that they report it to that precision. $\endgroup$
    – uhoh
    Jan 16 at 10:51

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