Amateur Telescope Research Articles

The Spectrum of C/2023 A3 Indicates a Depleted Composition

We report a spectroscopic observation of comet C/2023 A3 using an 80 mm apochromatic refractor equipped with a custom-built spectrometer with a resolution of R ∼ 2500 on the night of 2024 October 4. Sodium D lines were detected prominently, while no other emission lines, particularly carbon-bearing species, were observed, which suggests that comet C/2023 A3 may be carbon-depleted. The mobility and flexibility of our observational setup highlight the value of amateur telescopes in observing low-altitude targets like C/2023 A3 as a complement to professional facilities.

A giant umbrella-like stellar stream around the tidal ring galaxy NGC 922

Context. Tidal ring galaxies (TRGs) are rarely observed in the local universe due to their intrinsically transient nature. The tidal ring structures are the result of strong interactions between gas-rich stellar disks and smaller galactic systems, and do not last longer than ∼500 Myr. Therefore, these are perfect scenarios in which to look for the debris of recently accreted dwarf galactic systems. Aims. Our goal is to study the low surface brightness stellar structures around the TRG NGC 922 and to revise the hypothesis of its formation in light of these new data. Methods. We present new deep images of the TRG NGC 922 and its surroundings from the DESI Legacy survey data and from our observations with an amateur telescope. These observations are compared with results from high-resolution N-body simulations that were designed to reproduce an alternative formation scenario for this peculiar galaxy. Results. Our new observations unveil that the low surface brightness stellar tidal structures around NGC 922 are much more complex than reported in previous works. In particular, the formerly detected tidal spike-like structure at the north-east of the central galaxy disk is not connected with the dwarf companion galaxy PGC 3080368, which has been suggested as the intruder triggering the ring formation of NGC 922. The deep images reveal that this tidal structure mainly has a fainter giant umbrella-like shape, and thus it was formed from the tidal disruption of a different satellite. Using the broad-band g, r, and z DESI LS images, we measured the photometric properties of this stellar stream, estimating a total absolute magnitude in the r band of Mr = −17.0 ± 0.03 mag and a total stellar mass for the stream of between 6.9 and 8.5×108 M⊙. We performed a set of N-body simulations to reproduce the observed NGC922-intruder interaction, suggesting a new scenario for the formation of its tidal ring from the infall of a gas-rich satellite around 150 Myr ago. Finally, our deep images also reveal a tidal shell around the dwarf galaxy PGC 3080368, a possible fossil of a recent merger with a smaller satellite, which may suggest it is in its first infall towards NGC 922.

ПОКРИТТЯ ЗОРІ АСТЕРОЇДОМ (853) НАНСЕНІЯ 8 КВІТНЯ 2021 р.

Observations of occultations of stars by asteroids provide useful information about the shape and size of asteroids. Ground-based multisite observations are especially valuable in that regard. To this end, on the joint initiative of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine and Astronomical Observatory of Taras Shevchenko National University of Kyiv, the development of Ukrainian network of stellar occultation observing stations is currently underway. Asteroids vary greatly in size with small asteroids being dominating. Occultations by small asteroids are visible across a rather narrow path. In such a case, it will not be feasible to make use of the entire network. Moreover, it is not always possible to conduct observations using telescopes with the required primary mirror diameter and light-gathering power or those equipped with special high-speed cameras. First of all, it applies to asteroids small in diameter for which the shadow tracks may run far from stationary telescopes. If this is the case, amateur telescopes or movable systems are employed. The aperture of such telescopes does not enable to acquire observations of occultations of faint stars with short exposure times. However, any observations are useful as they may help to determine the limits of asteroid diameter directly using techniques typical for the photometry of stellar occultations. This paper presents the results of observations of the star UCAC4 516-047388 occultation by the asteroid (853) Nansenia on 8 April 2021 performed at the Kryzhanovka observation station of Odessa I.I. Mechnikov National University. This observing station will become a part of the network of stellar occultation observers which is currently being set up. A Schmidt telescope(D = 271.25 mm, F = 440 mm) and Videoscan-415-2001 CCD camera were used to carry out observations. The ICX415AL chip (with the number of effective pixels 782 (H) x 582 (V) and unit cell size of 8.3 μm x 8.3 μm) serves as an interline image sensor for the specified CCD camera. The spectral sensitivity of the CCD camera approximately corresponds to the visible range. The NTP based PC system clock was used for the frame time-stamping. A GPS receiver with a specialised application running in the background was used to set (synchronise) the imaging system computer clock. The exposure duration for the occultation recording was chosen to be 5 seconds in order to acquire an image of the star adequate for photometric measurements, on the one hand, but to minimise the exposure time thus improving temporal resolution, on the other hand. The star UCAC4 516-047388 has a low brightness of 14.2 m which provides another reason for a long exposure time of 5 seconds to be used. This exposure time exceeds the maximum duration of occultation of 2.8 sec. An approach that enables us to draw a conclusion that the occultation has taken place and also to estimate the duration of such a phenomenon is adopted to construe the photometric (light) curve. Our calculations yield the duration of occultation τ = 2.0 ± 1.2 sec, which corresponds to the predicted value within the error. This paper also provides a description of the custom software, designed to process observations of occultations in the form of a series of graphic (image) files, which was employed for the stellar occultation by the asteroid (853) Nansenia. This software application can also be used to process observations of amateurs who will become involved in observing stellar occultations.

Yuri Gagarin public astronomical observatory – the first in Bulgaria: 60 years later

The report presents an analysis of the history of the Public Astronomical Observatory (NAO) "Yuri Gagarin", the city of Stara Zagora, which was officially opened on February 26, 1961. The initiative to open it belongs to a group of enthusiasts, among which the figure of Boncho Bonev is of particular importance. With financial and material assistance from the municipality of Stara Zagora, the first premises were equipped and the first astronomical instruments and equipment were purchased. The observatory bears the name of the world's first pilot - cosmonaut Yuri Gagarin. The natural evolution of the development of the Observatory is presented, as well as the need of creation an observational base outside the city, in the area of the Ayazmo Park (opened in 1968). The supply with amateur telescopes is shown, as well as of a large optical instrument for professional astronomical work – a refractor (200/3000 mm), the Kude system, the production of the Carl Zeiss, Jena (former East Germany). The acquired ZKP-2 planetarium at the Carl Zeiss factory in Jena expands the NAO's capabilities in the education and promotion of astronomy and space science.The evolution of extracurricular astronomy training and the mass popularization of the achievements of astronomy, aeronautics, physics and human technology in PAOP are analyzed, as well as scientific observations of artificial Earth satellites. In this connection, in 1979 a specialized out-of-town observation base was built in the area of the Stara Zagora Mineral Baths, equipped with one of the most modern devices of its time – the AFU-75 satellite camera. An attempt was made to periodize the history of PAOP «Yu. Gagarin», the main stages being arranged in time according to significant historical, technological, organizational or other events.

A feather on the hat: tracing the giant stellar stream around the Sombrero galaxy

ABSTRACT Recent evidence of extremely metal-rich stars found in the Sombrero galaxy (M104) halo suggests that this galaxy has undergone a recent major merger with a relatively massive galaxy. In this paper, we present wide-field deep images of the M104 outskirts obtained with a 18-cm amateur telescope with the purpose of detecting any coherent tidal features from this possible major merger. Our new data, together with a model of the M104 inner halo and scattered light from stars around the field, allow us to trace for the first time the full path of the stream on both sides of the disc of the galaxy. We fully characterize the ring-like tidal structure and we confirm that this is the only observable coherent substructure in the inner halo region. This result is in agreement with the hypothesis that M104 was created by a wet major merger more than 3.5 Gyr ago that heated up the stellar population, blurring all old substructure. We generated a set of numerical models that reproduce the formation of the observed tidal structure. Our best-fitting model suggests the formation of this stream in the last 3 Gyr is independent of the wet major merger that created the M104 system. Therefore, the formation of the tidal stream can put a constraint on the time when the major merger occurred.

A Dozen new Dwarf Galaxy Candidates in the Local Volume

We carried out a survey of low-surface-brightness companions around nine luminous Local Volume galaxies using long exposures with small amateur telescopes. We found 12 low- and very low-surface-brightness objects around the galaxies: NGC 628, NGC 2337, NGC 3368, NGC 3521, NGC 4236, NGC 4258, NGC 4594, NGC 5055, and NGC 6744 situated within 12 Mpc from us. Assuming the dwarf candidates are satellites of the neighbouring massive galaxies, their absolute B magnitudes are in the range of [-8.9, -13.0], linear diameters are [0.6 - 2.7] kpc, and the mean surface brightnesses are [25.1 - 27.5] mag/sq.arecsec. The mean linear projected separation of satellite candidates from the host galaxies is 83 kpc.

A survey for variable young stars with small telescopes: II – mapping a protoplanetary disc with stable structures at 0.15 au

ABSTRACT The HOYS citizen science project conducts long-term, multifilter, high-cadence monitoring of large YSO samples with a wide variety of professional and amateur telescopes. We present the analysis of the light curve of V1490 Cyg in the Pelican Nebula. We show that colour terms in the diverse photometric data can be calibrated out to achieve a median photometric accuracy of 0.02 mag in broad-band filters, allowing detailed investigations into a variety of variability amplitudes over time-scales from hours to several years. Using Gaia DR2, we estimate the distance to the Pelican Nebula to be 870 $^{+70}_{-55}$ pc. V1490 Cyg is a quasi-periodic dipper with a period of 31.447 ± 0.011 d. The obscuring dust has homogeneous properties, and grains larger than those typical in the ISM. Larger variability on short time-scales is observed in U and Rc−H α, with U amplitudes reaching 3 mag on time-scales of hours, indicating that the source is accreting. The H α equivalent width and NIR/MIR colours place V1490 Cyg between CTTS/WTTS and transition disc objects. The material responsible for the dipping is located in a warped inner disc, about 0.15 au from the star. This mass reservoir can be filled and emptied on time-scales shorter than the period at a rate of up to 10−10 M⊙ yr−1, consistent with low levels of accretion in other T Tauri stars. Most likely, the warp at this separation from the star is induced by a protoplanet in the inner accretion disc. However, we cannot fully rule out the possibility of an AA Tau-like warp, or occultations by the Hill sphere around a forming planet.

A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes

Kuiper belt objects (KBOs) are thought to be the remnant of the early solar system, and their size distribution provides an opportunity to explore the formation and evolution of the outer solar system. In particular, the size distribution of kilometre-sized (radius = 1-10 km) KBO represents a signature of initial planetesimal sizes when planets form. These kilometre-sized KBOs are extremely faint, and it is impossible to detect them directly. Instead, monitoring of stellar occultation events is one possible way to discover these small KBOs. Hitherto, however, there has been no observational evidence for the occultation events by KBOs with radii of 1-10 km. Here we report the first detection of a single occultation event candidate by a KBO with a radius of $\sim$1.3 km, which is simultaneously provided by two low-cost small telescopes coupled with commercial CMOS cameras. From this detection, we conclude that a surface number density of KBOs with radii exceeding $\sim 1.2$ km is $\sim 6 \times 10^5 \ {\rm deg^{-2}}$. This surface number density favours a theoretical size distribution model with an excess signature at a radius of 1-2 km. If this is a true detection, this implies that planetesimals before their runaway growth phase grow into kilometre-sized objects in the primordial outer solar system and remain as a major population of the present-day Kuiper belt.

Mirach’s Goblin: Discovery of a dwarf spheroidal galaxy behind the Andromeda galaxy

Context. It is of broad interest for galaxy formation theory to carry out a full inventory of the numbers and properties of dwarf galaxies, both satellite and isolated, in the Local Volume. Aims. Ultra-deep imaging in wide areas of the sky with small amateur telescopes can help to complete the census of these hitherto unknown low-surface-brightness galaxies, which cannot be detected by the current resolved stellar population and HI surveys. We report the discovery of Donatiello I, a dwarf spheroidal galaxy located one degree from the star Mirach (β And) in a deep image taken with an amateur telescope. Methods. The color-magnitude diagram (CMD) obtained from follow-up observations obtained with the Gran Telescopio Canarias (La Palma, Spain) reveals that this system is beyond the local group and is mainly composed of old stars. The absence of young stars and HI emission in the ALFALFA survey is typical of quenched dwarf galaxies. Our photometry suggests a distance modulus for this galaxy of (m − M) = 27.6 ± 0.2 (3.3 Mpc), although this distance cannot yet be established securely owing to the crowding effects in our CMD. At this distance, the absolute magnitude (MV = −8.3), surface brightness (μV = 26.5 mag arcsec−2), and stellar content of Donatiello I are similar to the “classical” Milky Way companions Draco or Ursa Minor. Results. The projected position and distance of Donatiello I are consistent with this object being a dwarf satellite of the closest S0-type galaxy NGC 404 (“Mirach’s Ghost”). Alternatively, it could be one of the most isolated quenched dwarf galaxies reported so far behind the Andromeda galaxy.

The extraordinary composition of the blue comet C/2016 R2 (PanSTARRS)

We present a multi-wavelength study of comet C/2016 R2 (PanSTARRS). This comet was observed on 23 and 24 January 2018 with the IRAM 30 m telescope, and in January to March 2018 with the Nançay radio telescope. Visible spectroscopy was performed in December 2017 and February 2018 with small amateur telescopes. We report on measurements of CO, CH3OH, H2CO and HCN production rates, and on the determination of the N2/CO abundance ratio. Several other species, especially OH, were searched for but not detected. The inferred relative abundances, including upper limits for sulfur species, are compared to those measured in other comets at about the same heliocentric distance of ~2.8 AU. The coma composition of comet C/2016 R2 is very different from all other comets observed so far, being rich in N2 and CO and dust poor. This suggests that this comet might belong to a very rare group of comets formed beyond the N2 ice line. Alternatively, comet C/2016 R2 (PanSTARRS) could be the fragment of a large and differentiated transneptunian object, with properties characteristic of volatile-enriched layers.

The ray guns are coming

The U.S. Navy's most advanced laser weapon looks like a pricey amateur telescope. As it emerges from a chassis high on the USS Ponce to look out onto the daytime sky above the Persian Gulf, its operator sits in a darkened room elsewhere on the ship holding what looks like a game controller. The screen before him is showing a small boat floating near the Ponce, carrying a dark object. The infrared beam hitting the object is invisible, but you can see one spot grow brighter until the object suddenly explodes, sending metal shards spiraling into the water.

DGSAT: Dwarf Galaxy Survey with Amateur Telescopes

The connection between the bulge mass or bulge luminosity in disk galaxies and the number, spatial and phase space distribution of associated dwarf galaxies is a discriminator between cosmological simulations related to galaxy formation in cold dark matter and generalised gravity models. Here, a nearby sample of isolated Milky Way-class edge-on galaxies is introduced, to facilitate observational campaigns to detect the associated families of dwarf galaxies at low surface brightness. Three galaxy pairs with at least one of the targets being edge-on are also introduced. Approximately 60% of the catalogued isolated galaxies contain bulges of different size, while the remaining objects appear to be bulgeless. Deep images of NGC 3669 (small bulge, with NGC 3625 at the edge of the image) and NGC 7814 (prominent bulge), obtained with a 0.4 m aperture, are also presented, resulting in the discovery of two new dwarf galaxy candidates, NGC 3669–DGSAT–3 and NGC 7814–DGSAT–7. Eleven additional low surface brightness galaxies are identified, previously notified with low quality measurement flags in the Sloan Digital Sky Survey (SDSS). Integrated magnitudes, surface brightnesses, effective radii, Sersic indices, axis ratios, and projected distances to their putative major hosts are displayed. At least one of the galaxies, NGC 3625–DGSAT–4, belongs with a surface brightness of μr ≈ 26 mag arcsec-2 and effective radius >1.5 kpc to the class of ultra-diffuse galaxies (UDGs). NGC 3669–DGSAT–3, the galaxy with the lowest surface brightness in our sample, may also be an UDG.

RECEPTION AND DISSEMINATION OF AMERICAN AMATEUR TELESCOPE MAKING IN SWEDEN

This paper discusses the appropriation of the American Amateur Telescope Making (ATM) movement in Sweden in the 1940s and 1950s. A key player was the Swedish Astronomical Society, which in 1943, and inspired by the American example, launched a campaign to raise interest in ATM and disseminate the necessary knowledge amongst potential amateur astronomers. The campaign was successful and in just a few years it quadrupled the number of amateurs with access to telescopes. Swedish amateurs kept on building telescopes through the 1950s, but the activities then stalled with the introduction of cheap mass-market telescopes. The appropriation of ATM in Sweden is an important example of how technical innovations have shaped the course of amateur astronomy.

A Recount of Sunspot Groups on Staudach’s Drawings

We have examined the more than 1100 drawings of the solar disk made by the German amateur astronomer Johann Caspar Staudach during 1749 – 1799 and counted the spots on each image. Using the modern perception of how to group spots into active regions, we regrouped the spots as a modern observer would. The resulting number of groups was found to be higher on average by 25 % than the first count of groups performed by Wolf in 1857, which was used by Hoyt and Schatten (Solar Phys. 181, 491, 1998) in their construction of the group sunspot number. Compared to other observers at the time, Staudach’s drawings have a very low average number, about two, of spots per group, possibly indicating an inferior telescope that probably suffered from spherical and chromatic aberration, as would be typical of amateur telescopes of the day. We have initiated an ongoing project aiming at observing sunspots with antique telescopes having similar defects in order to determine the factor necessary to bring the Staudach observations onto a modern scale.

Making Telescopes and Partying with the Stars: Amateur Astronomy in Spain during Franco’s Dictatorship

Franco’s dictatorship was characterized by an official narrative that criminalized the liberal tradition of previous periods. Such a discourse defined an ideologically correct science that censured the subordination of Spanish science to foreign influence and sought to create a new scientific tradition. However, recent studies have revised these aims and suggest that there was a continuity of scientific and technological programmes and practices before and after the Spanish Civil War. This paper contributes to these investigations with further evidence, focusing on several practices that characterized the development of amateur astronomy during this period. Special attention is paid to the development of amateur telescope making, the popularization of astronomy, and attempts to define astronomy as a discipline for sociability that developed in alternative spaces for instruction and socialization – and so avoided direct control from the dictatorial regime.

Introduction: Planetary geosciences, the Dutch contribution to the exploration of our solar system

Planetary geoscience was effectively born when Christiaan Huygens took his first look at planet Mars on Friday 28 November 1659. As one of the leading scientists of his time, Huygens was known for constructing his own telescopes to observe stars, planets and nebulae whenever the clear and spacious skies above the Netherlands allowed. Huygens observed the planet Mars during the heydays of its 1659 opposition. On the night of 28 November he succeeded in sketching the first albedo feature on a different planet in our solar system. The roughly triangular dark-coloured patch was originally christened the Hourglass Sea, suggesting it to be an area of open water. Perhaps the landscape surrounding him in the Netherlands prompted Huygens to interpret the newly discovered feature as a wet area on the planet's surface. The attribution of traits to an albedo feature on another planet based on terrestrial landscapes may well be considered as the first-ever attempt at ‘comparative planetology’. The albedo feature can still be recognised at the surface of Mars today as Syrtis Major. Any modest amateur telescope can provide a view superior to that of Huygens’, allowing the observation of the very first geological feature ever identified on another rocky planet.

DISCOVERY OF AN ULTRA-DIFFUSE GALAXY IN THE PISCES-PERSEUS SUPERCLUSTER

ABSTRACT We report the discovery of DGSAT I, an ultra-diffuse, quenched galaxy located 10.°4 in projection from the Andromeda galaxy (M31). This low-surface brightness galaxy (μ V = 24.8 mag arcsec−2), found with a small amateur telescope, appears unresolved in sub-arcsecond archival Subaru/Suprime-Cam images, and hence has been missed by optical surveys relying on resolved star counts, in spite of its relatively large effective radius (R e (V) = 12″) and proximity (15′) to the well-known dwarf spheroidal galaxy And II. Its red color (V − I = 1.0), shallow Sérsic index (n V = 0.68), and the absence of detectable Hα emission are typical properties of dwarf spheroidal galaxies and suggest that it is mainly composed of old stars. Initially interpreted as an interesting case of an isolated dwarf spheroidal galaxy in the local universe, our radial velocity measurement obtained with the BTA 6 m telescope (V h = 5450 ± 40 km s−1) shows that this system is an M31-background galaxy associated with the filament of the Pisces-Perseus supercluster. At the distance of this cluster (∼78 Mpc), DGSAT I would have an R e ∼ 4.7 kpc and M V ∼ −16.3. Its properties resemble those of the ultra-diffuse galaxies (UDGs) recently discovered in the Coma cluster. DGSAT I is the first case of these rare UDGs found in this galaxy cluster. Unlike the UDGs associated with the Coma and Virgo clusters, DGSAT I is found in a much lower density environment, which provides a fresh constraint on the formation mechanisms for this intriguing class of galaxy.

DGSAT: Dwarf Galaxy Survey with Amateur Telescopes

Context: We introduce the Dwarf Galaxy Survey with Amateur Telescopes (DGSAT) project and report the discovery of eleven low surface brightness (LSB) galaxies in the fields of the nearby galaxies NGC 2683, NGC 3628, NGC 4594 (M104), NGC 4631, NGC 5457 (M101), and NGC 7814. Aims: The DGSAT project aims to use the potential of small-sized telescopes to probe LSB features around large galaxies and to increase the sample size of the dwarf satellite galaxies in the Local Volume. Methods: Using long exposure images, fields of the target spiral galaxies are explored for extended low surface brightness objects. After identifying dwarf galaxy candidates, their observed properties are extracted by fitting models to their light profiles. Results: We find three, one, three, one, one, and two new LSB galaxies in the fields of NGC 2683, 3628, 4594, 4631, 5457, and 7814, respectively. In addition to the newly found galaxies, we analyse the structural properties of nine already known galaxies. All of these 20 dwarf galaxy candidates have effective surface brightnesses in the range $25.3\lesssim\mu_{e}\lesssim28.8$ mag.arcsec$^{-2}$ and are fit with Sersic profiles with indices $n\lesssim 1$. Assuming that they are in the vicinity of the above mentioned massive galaxies, their $r$-band absolute magnitudes, their effective radii, and their luminosities are in the ranges $-15.6 \lesssim M_r \lesssim -7.8$, 160 pc $\lesssim R_e \lesssim$ 4.1 kpc, and $0.1\times 10^6 \lesssim\left(\frac{L}{L_{\odot}}\right)_r\lesssim127 \times 10^6$, respectively. To determine whether these LSB galaxies are indeed satellites of the above mentioned massive galaxies, their distances need to be determined via further observations. Conclusions: Using small telescopes, we are readily able to detect LSB galaxies with similar properties to the known dwarf galaxies of the Local Group.

Satellite accretion in action: a tidally disrupting dwarf spheroidal around the nearby spiral galaxy NGC 253

Abstract We report the discovery of NGC 253-dw2, a dwarf spheroidal (dSph) galaxy candidate undergoing tidal disruption around a nearby spiral galaxy, NGC 253 in the Sculptor group: the first such event identified beyond the Local Group. The dwarf was found using small-aperture amateur telescopes, and followed up with Suprime-Cam on the 8 m Subaru Telescope in order to resolve its brightest stars. Using g- and Rc-band photometry, we detect a red giant branch consistent with an old, metal-poor stellar population at a distance of ∼3.5 Mpc. From the distribution of likely member stars, we infer a highly elongated shape with a semimajor axis half-light radius of (2 ± 0.4) kpc. Star counts also yield a luminosity estimate of ∼2 × 106 L⊙,V (MV ∼ −10.7). The morphological properties of NGC 253-dw2 mark it as distinct from normal dSphs and imply ongoing disruption at a projected distance of ∼50 kpc from the main galaxy. Our observations support the hierarchical paradigm wherein massive galaxies continuously accrete less massive ones, and provide a new case study for dSph infall and dissolution dynamics. We also note the continued efficacy of small telescopes for making big discoveries.

Larger and faster: revised properties and a shorter orbital period for the WASP-57 planetary system from a pro-am collaboration

Transits in the WASP-57 planetary system have been found to occur half an hour earlier than expected. We present ten transit light curves from amateur telescopes, on which this discovery was based, thirteen transit light curves from professional facilities which confirm and refine this finding, and high-resolution imaging which show no evidence for nearby companions. We use these data to determine a new and precise orbital ephemeris, and measure the physical properties of the system. Our revised orbital period is 4.5s shorter than found from the discovery data alone, which explains the early occurrence of the transits. We also find both the star and planet to be larger and less massive than previously thought. The measured mass and radius of the planet are now consistent with theoretical models of gas giants containing no heavy-element core, as expected for the sub-solar metallicity of the host star. Two transits were observed simultaneously in four passbands. We use the resulting light curves to measure the planet's radius as a function of wavelength, finding that our data are sufficient in principle but not in practise to constrain its atmospheric properties. We conclude with a discussion of the current and future status of transmission photometry studies for probing the atmospheres of gas-giant transiting planets.