Questions tagged [photometry]

Questions regarding the measurement of the amount of light coming from astronomical objects.

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Is 486958 Arrokoth (2014 MU69 aka Ultima Thule) the only solar-system object determined to be binary by occultation?

The asteroid 486958 Arrokoth was discovered to be binary by astronomers lugging a bunch of telescopes around (I think) camping with them. The timing offered additional astrometry for the orbit ...
uhoh's user avatar
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How can I calculate the uncertainties in magnitude like the CDS does?

When you check an entry of the Gaia DR2 stellar catalogue in Vizier, for example this one, you can see that there is a value for the G magnitude (in our case 18.0733 mag) and a value for the ...
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How bright is the Crab Pulsar's 30 Hz modulation in visible light? What color is it?

This answer to Has great eyesight been necessary for astronomers? mentions Astronomer Jocelyn Bell Burnell's recounting of a likely first visual observation of a pulsar. This can be found for example ...
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Could mirrors be replaced with CCDs?

Why do telescopes use mirrors that simply reflect photons, when they instead could be covered with large sensors to register them? Reflection is all good and well, all thanks to silver and beryllium ...
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Did the late 2019 "fainting" of Betelgeuse show any spectral trends that differ from it's normal variability?

update: (August 2020) With all the newest news about including what the Dr. Becky video discusses as linked in How do magnetic fields mess with astronomers' observations? I'll bet this question ...
uhoh's user avatar
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Why does titanium oxide around Betelgeuse produce this particular sawtooth-shaped absorption spectrum?

Betelgeuse Just Isn’t That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse suggests that the recent dimming might be caused by increased optical absorption by dust ...
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Why do these photometric observations of Betelgeuse look "quantized" in 0.1 magnitude steps?

The most interesting question related to this Will Kinney tweet would be what's going on with Betelgeuse? but I can't help but wonder why much but not all of the photometric data is clustered in ...
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How fast is Neptune getting brighter? When was was this first noticed and reported?

This answer to Compute Planet's Apparent Visual Magnitude reports the new work on planetary magnitudes, and contains an intriguing blurb about Neptune: Neptune keeps getting brighter. No one knows ...
uhoh's user avatar
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3 votes
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How bright is Andromeda's center, in magnitudes per square arcminute or something similar?

I'd like to know how bright the Andromeda galaxy's core is as an extended object, not the total integrated brightness. Ideally a contour map or scan across the center might show brightness in ...
uhoh's user avatar
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Time domain astronomy and fastest eclipsing binary ZTF J1539+5027 (+20 mag, 6.91 minutes): How to measure its minimum brightness?

Per Wikipedia's ZTF J153932.16+502738.8 ZTF J153932.16+502738.8 is a double binary white dwarf with an orbital period of just 6.91 minutes. [...] The light curve shows eclipses. One dip in the light ...
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Are there home-brew photometers for amateur observing of variable stars and are they widely used?

Comments on Why do these photometric observations of Betelgeuse look “quantized” in 0.1 magnitude steps? suggest that these are visual estimates, mostly (but not all) to 0.1 magnitude resolution. Are ...
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IRAF Like software that work on Window

My professor asks to me install IRAF for the photometry project but We have a hard time installing it and also I'm more comfortable with the Windows environment (because there is other software that ...
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1 vote
1 answer
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Relationship between photometric colour and redshift

In this paper, the authors describe the theoretical relationship between photometric colours, particularly in Figures 1 and 6: Since the colour is the difference between two magnitudes, and the ...
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Has star KIC 8462852's 3 year long Kepler-fading continued after the primary Kepler mission ended?

BACKGROUND May 11, 2013 the Kepler space telescope ended its primary mission. Data captured until then showed that the now famous "Tabby's star" or "Boyajian's star" (KIC 8462852) had been fading ...
LocalFluff's user avatar
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What is equation of straight line for a ideal blackbody on the color color diagram?

The color-color diagram is a plot between $U-B$ vs $B-V$ values. For a ideal blackbody, what is the equation of this line? In other words, what does the linear relation between $U-B$ and $B-V$ look ...
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4 votes
2 answers
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Can you subtract magnitude of constant source to get magnitude of variable source?

Let's say I observe a source that is actually two sources (source A and source B) where each cannot be individually resolved. Source A is a variable source and source B is a constant source. I want to ...
theta's user avatar
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2 votes
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Are astronomers still using photomultiplier tubes for optical photometry?

In Time domain astronomy and fastest eclipsing binary ZTF J1539+5027 (+20 mag, 6.91 minutes) How to measure it's minimum brightness? I've written A logarithmic magnitude scale might tend to show ...
uhoh's user avatar
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Relationship between photometric colour and redshift, part two

In the graphs in my previous question here, there are negative-sloped regions as the colour-z relationship oscillates. So if I look at how the I-W2 and W3-U colours change with redshift, as I've done ...
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1 vote
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Acceptable errors in photometric measurements

As the title says, what is considered as an "acceptable" error in a photometric measurement (in magnitudes)? I know that it will depend a bit on the final use of the data, i.e., the photometric error ...
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Disk-integrated vs disk-resolved, what is the difference?

I'm trying to find online what is the difference between disk-integrated vs. disk-resolved, but I can't find a website which does explain them, especially in the context of modelling spectral flux ...
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